NTSB Safety Recommendation P-25-005

NTSB safety recommendation P-25-005.

TO THE 50 STATES, THE COMMONWEALTH OF PUERTO RICO, AND THE DISTRICT OF COLUMBIA: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak.

Priority: CLASS II

Overall Status: Open - Await Response

Issued Date: 2025-04-08

Adopted Date: 2025-03-18

Synopsis: This report discusses the March 24, 2023, natural gas–fueled explosion and fire at Building 2 of the R.M. Palmer Company, a candy manufacturer located in West Reading, Pennsylvania. The explosion destroyed the manufacturer’s Building 2 and caused significant structural damage to its adjacent Building 1 and other surrounding structures. In total, 7 people were killed, 10 people were injured, and 3 families were displaced from a neighboring apartment building. Safety issues identified in this report include degradation of a retired service tee, insufficient consideration of threats to pipeline integrity, the risk associated with unmarked private pipeline assets crossing public rights-of-way (for example, a public street), delayed evacuation of Building 2 despite detection of natural gas, natural gas safety messaging that may not reach certain members of the public, insufficient guidance on gas leak emergency procedures, absence of natural gas detection alarms in commercial buildings, and insufficient accessibility of gas distribution line valves. As part of this investigation, the National Transportation Safety Board issued recommendations to the Pipeline and Hazardous Materials Safety Administration, the Occupational Safety and Health Administration, 50 states along with the Commonwealth of Puerto Rico and the District of Columbia, the Commonwealth of Pennsylvania, the Pennsylvania Public Utility Commission, the American Gas Association, the American Petroleum Institute, the Gas Piping Technology Committee, the Common Ground Alliance, the International Code Council, the National Fire Protection Association, UGI Corporation, and R.M. Palmer Company.

Probable Cause: The National Transportation Safety Board determines that the probable cause of the explosion was degradation of a retired 1982 Aldyl A polyethylene service tee with a Delrin polyacetal insert that allowed natural gas to leak and migrate underground into the R.M. Palmer Company candy factory buildings, where it was ignited by an unknown source. Contributing to the degradation of the service tee and insert were significantly elevated ground temperatures from steam escaping R.M. Palmer Company’s corroded underground steam pipe, located near the service tee, that had been unmarked and cracked. Contributing to the steam pipe crack was soil movement and R.M. Palmer Company’s lack of awareness of the pipe’s corroded state. Contributing to the natural gas leak was UGI Corporation’s lack of awareness of the nearby steam pipe, which led to an incomplete integrity management program evaluation that did not consider or manage the risk posed by the steam pipe. Contributing to the accident’s severity was R.M. Palmer Company’s insufficient emergency response procedures and training of its employees, who did not understand the hazard and did not evacuate the buildings before the explosion.

Ntsbnumber: PLD23LR002

Report Number: PIR-25-01

Addressee Name: State of West Virginia

Addressee Status: Open - Await Response

Addressee Acronym: WV

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of West Virginia to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of West Virginia (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the

Addressee Acronym: WV

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: WV

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: WV

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Washington

Addressee Status: Open - Await Response

Addressee Acronym: WA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Washington to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Washington (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC w

Addressee Acronym: WA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: WA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: WA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Vermont

Addressee Status: Open - Await Response

Addressee Acronym: VT

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Vermont to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Vermont (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: VT

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: VT

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: VT

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Utah

Addressee Status: Open - Await Response

Addressee Acronym: UT

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Utah to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Utah (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with the

Addressee Acronym: UT

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: UT

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: UT

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Texas

Addressee Status: Open - Await Response

Addressee Acronym: TX

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Texas to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Texas (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with t

Addressee Acronym: TX

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: TX

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: TX

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of South Dakota

Addressee Status: Open - Await Response

Addressee Acronym: SD

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of South Dakota to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of South Dakota (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the I

Addressee Acronym: SD

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: SD

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: SD

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of South Carolina

Addressee Status: Open - Await Response

Addressee Acronym: SC

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of South Carolina to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of South Carolina (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended t

Addressee Acronym: SC

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: SC

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: SC

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Rhode Island

Addressee Status: Open - Await Response

Addressee Acronym: RI

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Rhode Island to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Rhode Island (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the I

Addressee Acronym: RI

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: RI

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: RI

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: Commonwealth of Pennsylvania

Addressee Status: Open - Await Response

Addressee Acronym: PA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the Commonwealth of Pennsylvania to act on the safety recommendations in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendations to the Commonwealth of Pennsylvania (additional information regarding these recommendations can be found in the noted sections of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) • Modify your Underground Utility Line Protection Law to require all owners and operators of pipelines transporting steam or other high-temperature materials located in public rights-of-way to register their assets with the Pennsylvania One Call System. (P-25-6) (See section 2.4.) • Review your statutes and amend them to clarify that confidential security information disclosure restrictions do not apply to the National Transportation Safety Board when it is conducting an accident investigation. (P-25-7) (See section 2.7.) The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendations by number (Safety Recommendations P-25-5 through -7). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to these recommendations. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5 through P-25-7). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the

Addressee Acronym: PA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: PA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: PA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Oregon

Addressee Status: Open - Await Response

Addressee Acronym: OR

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Oregon to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Oregon (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with

Addressee Acronym: OR

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: OR

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: OR

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Oklahoma

Addressee Status: Open - Await Response

Addressee Acronym: OK

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Oklahoma to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Oklahoma (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: OK

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: OK

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: OK

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Ohio

Addressee Status: Open - Await Response

Addressee Acronym: OH

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Ohio to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Ohio (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with the

Addressee Acronym: OH

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: OH

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: OH

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of North Dakota

Addressee Status: Open - Await Response

Addressee Acronym: ND

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of North Dakota to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of North Dakota (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the I

Addressee Acronym: ND

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: ND

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: ND

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of New Mexico

Addressee Status: Open - Await Response

Addressee Acronym: NM

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of New Mexico to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of New Mexico (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC w

Addressee Acronym: NM

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: NM

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: NM

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of New Jersey

Addressee Status: Open - Await Response

Addressee Acronym: NJ

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of New Jersey to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of New Jersey (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC w

Addressee Acronym: NJ

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: NJ

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: NJ

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of New Hampshire

Addressee Status: Open - Await Response

Addressee Acronym: NH

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of New Hampshire to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of New Hampshire (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the

Addressee Acronym: NH

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: NH

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: NH

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Nebraska

Addressee Status: Open - Await Response

Addressee Acronym: NE

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Nebraska to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Nebraska (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: NE

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: NE

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: NE

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Montana

Addressee Status: Open - Await Response

Addressee Acronym: MT

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Montana to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Montana (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response.

Addressee Acronym: MT

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: MT

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: MT

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Missouri

Addressee Status: Open - Await Response

Addressee Acronym: MO

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Missouri to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Missouri (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: MO

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: MO

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: MO

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Michigan

Addressee Status: Open - Await Response

Addressee Acronym: MI

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Michigan to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Michigan (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: MI

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: MI

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: MI

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: Commonwealth of Massachusetts

Addressee Status: Open - Await Response

Addressee Acronym: MA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the Commonwealth of Massachusetts to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the Commonwealth of Massachusetts (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We r

Addressee Acronym: MA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: MA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: MA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Maryland

Addressee Status: Open - Await Response

Addressee Acronym: MD

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Maryland to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Maryland (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: MD

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: MD

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: MD

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Maine

Addressee Status: Open - Await Response

Addressee Acronym: ME

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Maine to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Maine (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with t

Addressee Acronym: ME

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: ME

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: ME

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Louisiana

Addressee Status: Open - Await Response

Addressee Acronym: LA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Louisiana to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Louisiana (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC wor

Addressee Acronym: LA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: LA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: LA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Iowa

Addressee Status: Open - Await Response

Addressee Acronym: IA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Iowa to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Iowa (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with the

Addressee Acronym: IA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: IA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: IA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Indiana

Addressee Status: Open - Await Response

Addressee Acronym: IN

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Indiana to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Indiana (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: IN

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: IN

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: IN

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Illinois

Addressee Status: Open - Await Response

Addressee Acronym: IL

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Illinois to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Illinois (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: IL

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: IL

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: IL

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Idaho

Addressee Status: Open - Await Response

Addressee Acronym: ID

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Idaho to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Idaho (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with t

Addressee Acronym: ID

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: ID

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: ID

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Hawaii

Addressee Status: Open - Await Response

Addressee Acronym: HI

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Hawaii to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Hawaii (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with

Addressee Acronym: HI

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: HI

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: HI

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Georgia

Addressee Status: Open - Await Response

Addressee Acronym: GA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Georgia to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Georgia (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: GA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: GA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: GA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Florida

Addressee Status: Open - Await Response

Addressee Acronym: FL

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Florida to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Florida (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: FL

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: FL

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: FL

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Delaware

Addressee Status: Open - Await Response

Addressee Acronym: DE

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Delaware to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Delaware (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: DE

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: DE

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: DE

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of California

Addressee Status: Open - Await Response

Addressee Acronym: CA

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of California to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of California (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC w

Addressee Acronym: CA

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: CA

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: CA

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Arkansas

Addressee Status: Open - Await Response

Addressee Acronym: AR

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Arkansas to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Arkansas (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work

Addressee Acronym: AR

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: AR

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: AR

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Arizona

Addressee Status: Open - Await Response

Addressee Acronym: AZ

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Arizona to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Arizona (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: AZ

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: AZ

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: AZ

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Alaska

Addressee Status: Open - Await Response

Addressee Acronym: AK

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Alaska to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Alaska (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work with

Addressee Acronym: AK

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: AK

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: AK

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: State of Alabama

Addressee Status: Open - Await Response

Addressee Acronym: AL

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Alabama to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Alabama (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: AL

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: AL

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: AL

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Acronym: AL

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Name: Commonwealth of Puerto Rico

Addressee Status: Open - Await Response

Addressee Acronym: PR

Addressee Organization Type: L-Local Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Acronym: PR

Addressee Organization Type: L-Local Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: PR

Addressee Organization Type: L-Local Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: PR

Addressee Organization Type: L-Local Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the Commonwealth of Puerto Rico to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the Commonwealth of Puerto Rico (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recom

Addressee Name: District of Columbia

Addressee Status: Open - Initial Response Received

Addressee Acronym: DC

Addressee Organization Type: L-Local Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Acronym: DC

Addressee Organization Type: L-Local Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: DC

Addressee Organization Type: L-Local Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: DC

Addressee Organization Type: L-Local Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the District of Columbia to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the District of Columbia (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC

Addressee Acronym: DC

Addressee Organization Type: L-Local Government

Communication Date: 2025-10-21

Communication Type: Official Correspondence

Communication Contents: -From Melissa G. Shear, Acting Director, Washington, DC Highway Safety Office: After conferring with our Natural Gas utility Washington Gas, the District has an estimated 55,714 installations of Aldyl-A piping. The estimate is based on an analysis from the Company’s DIMP (Distribution Integrity Management Plan), which reflects the installation of Aldyl-A piping between approximately 1971 and 1995. Note that Aldyl-A was the predominate resin used during that time period, but was not used exclusively. This number corresponds to the count of plastic services with records reflecting installation within the defined window. As other resins were in limited use during the defined time period, this is an inclusive estimate. Without knowing how the NTSB defines congregate, we don’t know how many of these Aldyl-A pipes would be impacted by this recommendation. As the NTSB is aware, a substantial number of properties are not regulated by the District Government. While it’s possible for the District to verify the existence of the Aldyl-A piping on federal property, the District cannot regulate or enforce any potential changes that might come with the NTSB’s recommendation. Thank you for your concern and for bringing this to the District’s attention. The District will continue to work with the NTSB on this and other important issues. Should additional information be requested, the District is available.

Addressee Name: State of Wyoming

Addressee Status: Open - Initial Response Received

Addressee Acronym: WY

Addressee Organization Type: S-State Government

Communication Date: 2025-04-08

Communication Type: Transmittal Letter

Communication Contents: The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant accidents in other modes of transportation—railroad, highway, marine, and pipeline. We determine the probable cause of the accidents and issue safety recommendations aimed at preventing future accidents. In addition, we carry out special studies concerning transportation safety and coordinate the resources of the federal government and other organizations to assist victims and their family members affected by major transportation disasters. We are providing the following information to urge the State of Wyoming to act on the safety recommendation in this letter because we believe your organization can help reduce the risk of future accidents. For more information about the NTSB and our recommendation process, please see the attached one-page summary. This letter also includes information about our March 18, 2025, report, UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, NTSB/PIR-25/01. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. As a result of this investigation, we identified the following safety issues: • Degradation of a retired Aldyl A service tee that was accelerated by elevated ground temperatures from a corroded and cracked steam pipe nearby. • UGI Corporation’s insufficient consideration of pipeline integrity threats, particularly Aldyl A service tees with Delrin inserts at elevated temperatures. • Presence of unmarked and unreported private assets crossing public rights-of-way, excluding them from the Pennsylvania One Call System and increasing the risk of damage to them. • Delayed evacuation of Palmer’s Building 2 despite detection of natural gas by employees and others. • Natural gas safety messaging from pipeline operator public awareness programs that may not reach certain members of the public. • Insufficient guidance on natural gas emergency procedures. • Absence of natural gas alarms in commercial buildings. • Insufficient accessibility of gas distribution line valves. Accordingly, the NTSB makes the following safety recommendation to the State of Wyoming (additional information regarding this recommendation can be found in the noted section of the report): • Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) (See section 2.5.1.) The NTSB is vitally interested in this recommendation because it is designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter, detailing the actions you have taken or intend to take to implement this recommendation. When replying, please refer to the safety recommendation by number (Safety Recommendation P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply, including attachments, exceeds 20 megabytes, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. All communications regarding safety recommendations are stored by the NTSB and viewable by the public. Please do not send privileged or confidential communications in response to this recommendation. Responses marked as confidential or privileged (or similar designations) will be considered nonresponsive. In the likely event that your company uses auto generated and/or preformatted confidentiality statements on letterhead or outgoing e-mails, please include a statement in your letter indicating that the information can be publicly released. If you have concerns about this protocol, please contact us at ExecutiveSecretariat@ntsb.gov. The attached letter from the NTSB Chairman provides information about the March 18, 2025, report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at http://www.ntsb.gov. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days of the date of this letter detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendation by number (for example, P-25-5). We encourage you to submit your response to ExecutiveSecretariat@ntsb.gov. If your reply exceeds 20 megabytes, including attachments, please e mail us at the same address for instructions on how to send larger documents. Please do not submit both an electronic copy and a hard copy of the same response. From the report UGI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania, March 24, 2023, PIR-25-1: 2.5.1 Natural Gas Alarms Public awareness is an effective tool to encourage adoption of safety devices like natural gas alarms. The first edition of API RP 1162 requires that public awareness programs include safety messages about the awareness of hazards and prevention measures as well as leak recognition and response but does not specifically require these programs to disseminate safety messages about natural gas alarms. UGI’s public awareness materials distributed before the accident were consistent with federal regulations, and although the materials promoted the use of smoke and carbon monoxide alarms, they did not address natural gas alarms. Following the accident, UGI now includes safety messages encouraging the purchase of natural gas alarms in its public awareness materials. The NTSB concludes that installing natural gas alarms can alert people of a gas leak so they can evacuate the area; however, natural gas customers may not be aware of the necessity of such alarms. The NTSB believes that messages about the benefits of natural gas alarms are critically important and could save lives when natural gas alarms are installed. The NTSB further believes that the natural gas industry can help shape the effectiveness of public awareness program delivery methods so that people in businesses, schools, residences, and other places of congregation are better informed, both about natural gas hazards and the necessity of natural gas alarms. The American Gas Association, which represents natural gas pipeline operators throughout the US, can facilitate industry efforts to improve public awareness program delivery methods and to improve safety, most critically through increasing the installation of natural gas alarms. Therefore, the NTSB recommends that the American Gas Association share the details of the March 24, 2023, natural gas–fueled explosion and fire in West Reading, Pennsylvania, with its members, encouraging them to evaluate the effectiveness of their current delivery methods of public awareness programs and to promote the installation of natural gas alarms in businesses, residences, and other places of congregation that they serve. Evacuation should occur immediately upon detection of the presence of natural gas. In 1976, the NTSB made its first recommendation to require natural gas detection to provide early warning of leaks. Most recently, after a 2016 building explosion in Silver Spring, Maryland, and then again after the 2018 home explosion in Dallas, we made recommendations to the ICC and the NFPA to require natural gas alarms with methane detection in residences (NTSB 2019). We recommended the ICC work wi

Addressee Acronym: WY

Addressee Organization Type: S-State Government

Communication Date: 2026-04-07

Communication Type: Recommendation Mention

Communication Contents: Pipeline Investigation Report PIR-26-02, “Enbridge Inc. Natural Gas–Fueled Home Explosion and Fatality, South Jordan, Utah, November 6, 2024” published on April 7, 2026: 2 Analysis On November 6, 2024, a natural gas–fueled home explosion fatally injured one resident and damaged nearby homes. A crack in the 4-inch-diameter Aldyl A gas main near the home allowed natural gas to leak and fuel the home explosion. The NTSB found that the crack originated on the inner surface of the pipe and aligned directly with an oblong impression on the outer surface. Investigators determined that a rock impingement likely caused the oblong impression on the outer surface of the pipe and the resulting crack. They also found that the crack growth features indicated that the crack breached the outer surface in a single abrupt event. As a result, the pipe rapidly transitioned from releasing no gas to releasing up to 48.7 scfm, as measured in the lab. Footnote: The actual leak rate may have been lower, given that the pipeline was buried in soil, which would constrain the pipe and provide back-pressure resistance to gas as it leaked from the pipe. Post-explosion, subsurface gas readings showed that the natural gas migrated about 150 feet from the leak location to the home. Although the exact timing of the leak could not be determined, the residents’ observations of physical symptoms, inability to relight the basement water heater, and an unusually high candle flame before the accident suggest that natural gas may have been present in the home for at least 3 days before the explosion. On November 6, the flammable natural gas–air mixture ignited in the southwest quadrant of the basement. The Utah Deputy State Fire Marshal identified two possible sources of the ignition: a water heater and a furnace. The water heater was turned off at the control point, so the only credible ignition source was the furnace. Footnote: The furnace control valve was found postaccident to have significant thermal damage, consistent with it being the ignition source. Before the accident, Enbridge had implemented safeguards to mitigate the consequences of leaks, including periodic leak surveys, timely response to odor complaints, and targeted replacement projects. However, none of these strategies proved effective for this scenario, because of the following issues related to the strategies: • Periodic leak surveys. Regulators require distribution leak surveys to be conducted every 5 years. Enbridge conducted its most recent leak survey on April 29, 2022—two years before the accident. However, in this accident, through-wall crack propagation occurred too rapidly, causing the leak to go undetected before the explosion. • Timely response to odor complaints. Regulators require odorization of natural gas in distribution systems to help alert the public to natural gas leaks. During interviews conducted by investigators, the NTSB determined that the local residents had not smelled natural gas odorant near the accident home, even though gas was determined to have permeated the ground in the area during postaccident surveys, indicating that the odorant had been stripped from the leaked natural gas that ultimately entered the home. Footnote: Field testing of the gas in the distribution system after the explosion found acceptable odorant concentrations. Although odorant can act as an early warning of a gas release to prevent an explosion and fire, it has been known to become depleted when traveling through soil, as it did in this accident. Previous NTSB investigations have identified occurrences of odorant depletion that allowed natural gas leaks to go undetected, resulting in explosions in Dallas, Texas, in 2018 and in Silver Spring, Maryland, in 2016. Footnote: NTSB. 2021. Atmos Energy Corporation Natural Gas–Fueled Explosion, Dallas, Texas, February 23, 2018. PAR-21/01. Washington, DC: NTSB. Footnote: NTSB. 2019. Building Explosion and Fire, Silver Spring, Maryland, August 10, 2016. PAR-19/01. Washington, DC: NTSB. • Targeted replacement projects. A 2014 California Public Utilities Commission study showed that the vintage of Aldyl A present in this accident, with stress concentrations from rock impingement, squeeze-off, bending, or deflection, were statistically predicted to fail between 22 and 235 years after installation. Footnote: California Public Utilities Commission 2014 Hazard Analysis and Mitigation Report On Aldyl A Polyethylene Gas Pipelines in California. Haine 2014. Because the estimated failure time is imprecise (a range of more than 200 years), and because some environmental conditions—such as the locations of rocks in the backfill material—are unknown, the Enbridge evaluation of the cracking threat to the 1976 vintage Aldyl A did not accurately characterize the risk of rock impingements and prevented Enbridge from identifying effective mitigative actions and targeted replacement projects. Even though Enbridge worked continuously to search for the leak after the explosion, it took them more than 21 hours to find and isolate the natural gas leak. During this time, the pipeline continued to leak natural gas into the ground, increasing the risk to nearby residents, first responders, and others operating in the area. When an underground natural gas pipeline leak occurs rapidly, it can be difficult to safeguard against. Natural gas alarms can provide an early warning of natural gas leaks inside nearby structures and can alert the building occupants to take immediate safety actions. Had in-home natural gas alarms been installed in the homes involved in this accident, they would have alerted the residents to a potential problem and prompted them to evacuate and call 911, reducing or eliminating the fatal consequences of the explosion. The NTSB has previously recommended requiring the installation of natural gas alarms in businesses, residences, and other buildings (Safety Recommendation P 25 05).

Addressee Acronym: WY

Addressee Organization Type: S-State Government

Communication Date: 2026-06-05

Communication Type: Recommendation Mention

Communication Contents: Atmos Energy Corporation Natural Gas–Fueled Home Explosion Pipeline Investigation Report PIR-26-03 published on June 5, 2026: Analysis The explosion and fire occurred after natural gas leaked from a fractured buried main, migrated through an uncapped underground sewer lateral, entered the accident home, and reached an explosive concentration near an unknown ignition source. The investigation did not identify issues with gas pressures in the area of the leak or the timeliness or efficacy of the local emergency response agencies. Postaccident bar-hole testing and excavations found only one source of natural gas: a leak in the gas main near a valve box on the eastern edge of the construction site. On-site examinations of the main found that it was fractured around most of its circumference with a thin strip of metal at the top (12 o’clock position) joining the southern section of pipe to the section still threaded into the valve body. This indicates tension—a stretching force—at the bottom of the pipe along its long axis. Tension along the bottom of the pipe is consistent with a bending stress created by an external downward force. Based on information provided to Atmos by the construction superintendent, a cement truck ran over a valve box at the leak’s location immediately before he heard and smelled natural gas being released. The investigation did not identify another plausible external force that could have damaged the main. The Materials Laboratory examination of the main found fracture characteristics typical of fast crack growth and no signs of significant corrosion or preexisting structural damage that could have contributed to the failure. The fracture was therefore consistent with a sudden application of force by the valve box to the main. Based on the fracture’s location, timing, and fast-cracking characteristics, the valve box transmitted part of the cement truck’s weight to the gas main, causing the main to fracture and leak. Examination of the gas main and valve box involved in this accident found coal tar coating the main and deposited on the bottom edge of the valve box. This indicates that the valve box was in contact with the main. The presence of coal tar alone does not indicate when the contact occurred, but the evidence is consistent with the valve box being installed in contact with the main and therefore able transmit the cement truck’s weight directly to the main near the fracture’s location. Federal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be installed in a manner that transmits external loads to mains, and valve boxes are normally installed with a buffer of soil or other protection between the valve box and the assets immediately below. For example, Atmos’s newer valve boxes are installed with support and base pads to prevent load transmission. However, Atmos was not actively replacing cast iron valve boxes with this newer design. Further, the maintenance crew that removed and reinstalled the valve box about 2 months before the accident did not have a specific standard to follow for reinstalling cast iron valve boxes other than an expectation that the top of the valve box be level with the grade. The lack of a standard likely led to the common reinstallation of valve boxes in contact with mains, as described by an Atmos vice president of operations. If Atmos had adopted either a standard for safely installing cast iron valve boxes or a policy of replacing cast iron valve boxes with the newer design, the protective buffer of soil or support pad would have reduced the load transmitted to the pipe on the day of the accident. There is not enough evidence to determine whether a buffer or pad would have prevented the accident, but it would have made the infrastructure more resilient. Atmos has not reported making changes to its valve box installation practices. After the main fractured, gas propagated undetected through an uncapped underground sewer lateral into the sewer system and then into the accident home, where it reached an explosive concentration. The gas in the sewers remained undetected because Atmos personnel did not test the atmosphere in the sewers prior to the explosion. For about 35 minutes, most of the time between the initial leak and the explosion, there was only one Atmos employee on the scene: an experienced senior service technician. He was equipped with a CGI and checked nearby storm drains for the presence of gas, which was one step in Atmos’s subsurface leak investigation procedure. During his interview with the NTSB, he described planning to check the sewers, another required step, but said that he had already confirmed that there was no threat to life or property. His activities after checking the storm drains are also consistent with a belief that he had finished assessing the risk posed by the leak: he switched to the non-safety-critical work of recording billing information for the damage. The investigation did not find evidence of a natural gas alarm in the accident home, which did not have gas service but was still impacted by a leak from a gas main. It is likely that a natural gas alarm would have provided the home’s occupants with warning of accumulating natural gas and given them an opportunity to evacuate before the explosion. The NTSB has advocated wider installation and use of natural gas alarms for nearly 50 years, including following the investigation into a pair of 2024 home explosions in Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the NTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: See CAROL for the complete history and current status of this recommendation. The NTSB also recommended that Atmos “develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas” (P-26-10).11F Footnote: See CAROL for the complete history and current status of this recommendation.

Addressee Acronym: WY

Addressee Organization Type: S-State Government

Communication Date: 2026-03-26

Communication Type: Recommendation Reiteration

Communication Contents: From the Report, “Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires Jackson, Mississippi, January 24, 2024, and January 27, 2024” published on March 26, 2026. Absence of Natural Gas Detection Alarms in Buildings The Bristol Boulevard accident home and the Shalimar Drive accident home did not have natural gas alarms installed. For nearly 50 years, the NTSB has been recommending natural gas alarms for the early detection of natural gas leaks. In the West Reading accident, several candy factory employees told the NTSB that they had smelled natural gas odorant and did not call 9 1 1 or the gas company but stayed in the building until the explosion occurred. Some of the employees inquired with their managers about what to do, and their managers were equally unaware of the actions to take during a suspected natural gas leak. In the two Jackson accidents, and in many of the pipeline accidents the NTSB has investigated for the last 5 decades, people smelled natural gas odorant and either did not know what actions to take, or they knew the actions necessary to address a potential natural gas emergency but did not execute them. Natural gas distribution pipeline operators must educate the public on pipeline safety through public awareness programs. It is also necessary, however, to have safeguards in place when members of the public (1) smell natural gas odorant and do not take the appropriate safety actions and (2) do not smell natural gas odorant, as was the case in the NTSB investigation of the Dallas accident, and therefore do not take appropriate safety actions. Footnote: The NTSB’s Dallas investigation determined that the occupants in the accident homes did not smell natural gas odorant because it was absorbed and depleted in the soil. Natural gas alarms are safeguards in protecting the public, which is why the NTSB has recommended their installation after many of our pipeline accident investigations. The NTSB found that natural gas alarms likely would have prevented or reduced the consequences of the Dallas and West Reading accidents, and the evidence in this investigation suggests the same. The Shalimar Drive accident home was empty at the time of that accident; however, when the explosion in the Bristol Boulevard accident home occurred, two people were inside. Therefore, the NTSB concludes that had a natural gas alarm been installed inside the Bristol Boulevard accident home, it could have alerted occupants that natural gas was present, prompting them to evacuate and report the leak, making Atmos aware that the leak had likely worsened and required corrective action. As a result of the West Reading investigation, the NTSB recommended that the 50 States, the Commonwealth of Puerto Rico, and the District of Columbia: Require the installation of natural gas alarms that meet the specifications of National Fire Protection Association 715 in businesses, residences, and other buildings where people congregate that could be affected by a natural gas leak. (P-25-5) Footnote: Safety Recommendation P-25-5 is currently classified Open—Await Response. As of this report, 7 states and the District of Columbia have provided an initial response; 43 states and the Commonwealth of Puerto Rico have not responded. Footnote: The seven states that have provided an initial response include Colorado, Connecticut, Kansas, Nevada, North Carolina, Virginia, and Wyoming. Mississippi, the state where the two Jackson accidents occurred, is one of the 43 states that have not provided an initial response. The NTSB investigation of the two Jackson accidents has again identified the critical importance of natural gas alarms to alert occupants to natural gas leaks. Therefore, the NTSB reiterates Safety Recommendation P 25-5 to 50 States, the Commonwealth of Puerto Rico, and the District of Columbia. As discussed in section 1.10.1.1, after the Avondale accident, Atmos reported that it provided the public with information, through its website, on the availability of natural gas alarms. However, Atmos can do more to safeguard the public in its distribution areas. The NTSB is aware of multiple natural gas distribution operators that have made natural gas alarms available to people in their service areas. Footnote: Visit http://www.ntsb.gov to find additional information in the public docket for this NTSB accident investigation (case number PLD24FR003). Therefore, the NTSB recommends that Atmos develop and implement a program that makes natural gas alarms available to members of the public who reside in its distribution areas.

Addressee Acronym: WY

Addressee Organization Type: S-State Government

Communication Date: 2025-07-21

Communication Type: Official Correspondence

Communication Contents: -From Mark Gordon, Governor of Wyoming: This letter is in response to the National Transportation Safety Board Safety Recommendation P-25-5, regarding the GI Corporation Natural Gas-Fueled Explosion and Fire, West Reading, Pennsylvania. As requested, attached to this letter is a response to the NTBS recommendation provided by the Wyoming Department of Fire Prevention and Electrical Safety. Wyoming is committed to policies that ensure public safety; however, we do not intend to adopt the rule at this time. Our State Fire Marshal has identified that the code mentioned in the letter is relatively new as it was introduced in 2023. The National Standards along with the International Codes Council Codes do not currently require Natural Gas Alarms in buildings. Some states are in the process of passing legislation to mandate Natural Gas Alarms in buildings, but previous efforts have failed in Wyoming. Wyoming only adopts the most recent standards published by the National Fire Protection Association and the International Code Council. It is the State Fire Marshal's advice that Safety Recommendation P-25-5 is presented to the Fire Code Action Committee of the Plumbing/Mechanical/Gas Code Action Committee for consideration. Please see the State Fire Marshall's letter for full details. I appreciate your correspondence with our office. -From Byron Matthews, Wyoming State Fire Marshall, Director Fire Prevention and Electrical Safety: The Department of Fire Prevention and Electrical Safety supports all efforts to ensure and enhance the public safety and reduce the risks to the entire state. We also support the need for updated and improved safety within structures. Thanks for allowing us to provide input into the findings of the investigation after the explosion in West Reading, Pennsylvania. If the recommendation from the NTSB is to install natural gas alarms in all structures we appreciate that recommendation. The best way to accomplish that recommendation is to work with both the Standards and Codes group to address new construction as well as how to attempt to address the retro-fit of these alarms. The State of Wyoming adopts the most recent standards published by the National Fire Protection Association as well as the International Code Council, for life safety and building construction. The current National Standards as well as The International Code Council Codes do not have any requirements for the installation and maintenance of Natural Gas Alarms. We would welcome a partnership with the National Association of State Fire Marshals and the Standards and Codes committees that would be able to address these devices. At this time the National Association of State Fire Marshals continues to work with the NTBS and the Standards and Model Code Committees to determine the correct action forward. The NFPA code that is referenced in the letter is a relatively new standard, first introduced in 2023. We are aware of the work that The Chemical Safety Board has done previously with the International Code Council .. When that work was done the expectation was to have them present their recommendations to the Fire Code Action Committee and/or the Plumbing/Mechanical/Gas Code Action Committee to see if either committee is interested in bringing forward a code change proposal. Past code change proposals to require natural gas alarms in all buildings have failed. Some states do have requirements however the intent seems to be to ensure that all states are afforded this level of protection and in order to do so then it would need to be addressed in the Standards and Model Codes. Two jurisdictions who have legislation or requirements are Maine and NYC both have addressed natural gas alarms in buildings with natural gas appliances, and Illinois has similar legislation pending. It is worth noting that the West Reading incident was the result of an underground pipeline leak that migrated through the ground into the building-and was not related to failures of any building systems. In cases like this, determining whether a building "could be affected by a natural gas leak" due to proximity to distribution pipelines could prove to be a monumental undertaking. All of this information being provided it is our recommendation that the State of Wyoming will wait until the Standards and Codes address this through the consensus code process. There are many impacts to this type of legislation outside of the code process as this change would have impacts on new and existing buildings across the State and the code process allows for the stakeholders affected to have a chance to present and have their concerns heard.

Addressee Name: State of Wisconsin

Addressee Status: Open - Initial Response Received