{"operation":"document","citation":"PLD25FR002","title":"Atmos Energy Corporation Natural Gas–Fueled Home Explosion","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2026-06-12","effective_on":"2024-12-02","summary":"Accident. in Avondale, LA, USA. on 2024-12-02. Atmos Energy. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-pld25fr002.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-pld25fr002.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-pld25fr002","source_url":"https://www.ntsb.gov/investigations/Pages/PLD25FR002.aspx","body":"NTSB investigation PLD25FR002.\n\nEvent Type: Accident\n\nEvent Date: 2024-12-02\n\nEvent City: Avondale\n\nEvent State Or Region: LA\n\nEvent Country: USA\n\nPipeline Operator: Atmos Energy\n\nPipeline Type: Distribution\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PIR2603\n\nReport Date: 2026-05-27\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the Avondale, Louisiana, home explosion was the release and underground migration of natural gas from a gas main that failed when a cement truck drove over a valve box that the Atmos Energy Corporation installed in contact with the gas main; the valve box transmitted the truck’s weight to the main and fractured it. Contributing to the severity of the accident was the Atmos Energy Corporation’s failure to identify the underground migration of gas during its leak investigation and to recognize the need to evacuate structures outside the immediate area of the leak.\n\nTier1Name: Emergency response\n\nTier2Name: Evacuation\n\nTier1Name: System operating\n\nTier2Name: Fire/explosion (post-release)\n\nTier1Name: System operating\n\nTier2Name: Product leak/release\n\nTier1Name: System operating\n\nTier2Name: External/third-party damage\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Valves\n\nFinding Modifier Name: Incorrect service/maintenance\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Valves - Incorrect service/maintenance\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Task performance\n\nFinding Tier3Name: Workload management\n\nFinding Modifier Name: Other company personnel\n\nFinding Report Text: Personnel - Task performance - Workload management - Other company personnel\n\nFinding Tier1Name: Personnel\n\nFinding Tier2Name: Miscellaneous\n\nFinding Tier3Name: (general)\n\nFinding Modifier Name: Equipment/vehicle operator\n\nFinding Report Text: Personnel - Miscellaneous - (general) - Equipment/vehicle operator\n\nOfficial NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations.\n\nWhat Happened\nOn December 2, 2024, about 6:26 a.m., a natural gas explosion and fire destroyed a single-family residence at 535 Avondale Garden Road in Avondale, Louisiana. The Atmos Energy Corporation provided natural gas service in the area, but the destroyed residence did not have gas service. One person was fatally injured, and five other people sustained injuries. A neighboring residence was damaged, and its residents were displaced.\n\nWhat We Found\nWe determined that the probable cause of the Avondale, Louisiana, home explosion was the release and underground migration of natural gas from a gas main that failed when a cement truck drove over a valve box that the Atmos Energy Corporation installed in contact with the gas main; the valve box transmitted the truck’s weight to the main and fractured it. Contributing to the severity of the accident was the Atmos Energy Corporation’s failure to identify the underground migration of gas during its leak investigation and to recognize the need to evacuate structures outside the immediate area of the leak.\n\nLessons Learned\nFederal regulations require that valve boxes be installed such that they do not transmit external loads to buried natural gas assets, as occurred in the Avondale accident. Natural gas operators can improve safety by making sure that employees have the tools, knowledge, and clear procedures they need to comply with federal regulations when installing or maintaining valve boxes, and by taking every opportunity to update legacy valve boxes with modern designs and materials.\n\nThe unidentified danger of underground gas migration in the Avondale accident illustrates the importance of completing a thorough leak investigation before shifting to non-safety-critical tasks. Operators can protect the quality of leak investigations through means such as oversight, regular training, and work aids to ensure employees know and follow leak response procedures.\n\nThis accident also underscores the value of natural gas alarms even in buildings that do not have natural gas service but are located near natural gas assets. Natural gas alarms provide both early warning of dangerous gas concentrations and a last line of defense when a leak investigation fails to identify a hazard. Further information about natural gas alarms is available on the NTSB website.\n\nPIR-26-03\n<<<PAGE 1>>>\n\nPipeline Investigation Report\nPIR-26-03\nIssued: May 27, 2026 Pipeline Investigation Report: PIR-26-03\nAtmos Energy Corporation Natural Gas–\nFueled Home Explosion\nLocation Avondale, Louisiana\nDate December 2, 2024\nAccident type Leak/explosion/fire\nPipeline Distribution pipeline\n2-inch coated steel main carrying natural gas\nFatalities 1\nInjuries 5\nFactual Information\n1.1 The Accident\nOn December 2, 2024, about 6:26 a.m., a natural gas explosion and fire\ndestroyed a single-family residence (the accident home) at 535 Avondale Garden Road\nin Avondale, Louisiana.1 (See figure 1.) One person was fatally injured, and five other\npeople sustained injuries. A neighboring residence was damaged, and its residents were\ndisplaced. At the time of the explosion, the weather was clear with winds of 11 mph; the\nweather was 50°F with no precipitation.\n1 (a) Visit ntsb.gov to find additional information in the public docket for this NTSB accident\ninvestigation (case number PLD25FR002), including detailed factual reports about the circumstances of the\naccident. (b) All times in this report are local.\n1\n\n<<<PAGE 2>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 1. Accident home after the explosion and fire. (Source: Atmos.)\nThe pipeline involved in this accident was owned and operated by the Atmos\nEnergy Corporation. The pipeline consisted of 2-inch coated (wrapped) steel main\nrunning under an unpaved area near the western edge of Avondale Garden Road.\n2\nOn the morning of the explosion, work was underway on a construction site on\nthe west side of Avondale Garden Road south of the accident home. About 5:00 a.m.,\nthe construction superintendent called Atmos and reported that a gas valve at the\nconstruction site had been run over by a cement truck, and that he could hear a hissing\nnoise and smell a strong gas odor.\n3 The superintendent called 9-1-1 about 5:09 a.m. and\nprovided the same information to Jefferson Parish dispatch.\nThe gas valve mentioned by the construction superintendent was about 2 feet\nunderground and about 340 feet from the accident home. (See figure 2.) The asset at\n2 A main is a pipeline that conveys natural gas to service lines that provide gas to houses or other\nbuildings.\nmeasure.\n3 Natural gas is odorless, but operators use additives to give it a distinct rotten-egg smell as a safety\n2\n\n<<<PAGE 3>>>\n\nPipeline Investigation Report\nPIR-26-03\ngrade-level was a valve box: a lidded, roughly cylindrical steel enclosure extending\nupward from the valve to the grade to enable access to the valve.\nFigure 2. Overhead view of accident site. (Source: Atmos.)\nThe first emergency responder on the scene was the assistant fire chief of the\nHerbert Wallace Volunteer Fire Company, who arrived about 5:17 a.m., followed shortly\nby personnel from the Jefferson Parish Sheriff’s Office (JPSO). When interviewed by the\nNational Transportation Safety Board (NTSB), the assistant fire chief said that the\nsuperintendent showed him the leak and confirmed that Atmos had been notified. The\nassistant fire chief and local law enforcement consulted the Emergency Response\n3\n\n<<<PAGE 4>>>\n\nPipeline Investigation Report\nPIR-26-03\nGuidebook published by the US Department of Transportation and blocked off nearby\nintersections to prevent traffic from approaching within 300–350 feet of the leak.\n4\nAn Atmos senior service technician arrived on the scene about 5:35 a.m., tested\nfor gas in storm drains near the leak, and performed bar-hole testing between the valve\nbox and 4th Street.5 These tests did not detect natural gas in the ground or drains. When\ninterviewed by the NTSB, the senior service technician said that these test results\nindicated that there was “not a threat to life or property at the time.\n” He still attempted to\npersuade the construction workers at the site to cease work for their own safety, but they\ndid not leave the scene. During the same period, he obtained a license plate number for\nthe truck that ran over the valve box, viewed a photograph of the driver’s license, and\ncollected contact information for the driver’s supervisor for billing purposes. During his\ninterview, the senior service technician stated that he was planning to check the sewers\nfor gas after recording the billing-related information; he said he had not been able to\nfind a sewer manhole when he first arrived.\n6\nBetween 6:00 a.m. and 6:15 a.m. an Atmos crew leader and an Atmos field\nconstruction coordinator arrived on the scene. At 6:17 a.m., the crew leader submitted\nan emergency locate ticket to the 811 call center and retrieved locating equipment from\nhis vehicle to verify the locations of underground assets and support emergency\nrepairs.\n7\nAbout 6:26 a.m., the accident home exploded and began to burn. Emergency\nresponders on scene responded to the fire, and Jefferson Parish dispatched personnel\nfrom additional agencies to provide aid, including the Avondale Volunteer Fire\nDepartment (VFD), Bridge City VFD, Nine Mile Point VFD, and Live Oak Manor VFD. The\nHerbert Wallace Volunteer Fire Company assistant fire chief served as the incident\ncommander. Over the next 30 minutes, emergency responders applied water to the fire\n4 The 2024 Emergency Response Guidebook recommends an isolation distance of at least 100 meters\n(330 feet) for flammable gas spills or leaks.\n5 Bar-hole testing describes a gas measurement technique in which a small-diameter hole is made in\nthe ground and a gas detection probe is inserted into the hole.\n6 The nearest sewer manhole was about 45 feet south of the valve box on the west side of Avondale\nGarden Road.\n7 (a) 811 call centers relay information about planned excavations to local utilities to help prevent\ndamage; in Louisiana, this service is provided by Louisiana 811. (b) Locating equipment is used to identify\nand mark the horizontal and vertical position of buried pipelines and other utilities to prevent excavation\ndamage.\n4\n\n<<<PAGE 5>>>\n\nPipeline Investigation Report\nPIR-26-03\nand searched the accident home for survivors. The Jefferson Parish Sheriff’s Office\ntransported four victims with burn injuries to local hospitals, the last at 6:58 a.m.\nAt 7:01 a.m., the assistant fire chief informed dispatch that the fire was under\ncontrol. Emergency responders conducted another search of the accident home and\nfound a deceased victim in the kitchen.\nAfter the fire was under control, emergency responders continued to smell\nnatural gas odorant in the air. Another Atmos senior service technician arrived on the\nscene about 7:25 a.m. and used a combustible gas indicator (CGI) to measure the\nconcentration of natural gas in a house adjacent to the accident home and in the\naccident home’s sewer cleanout.\n8 The readings indicated 100% gas in the sewer\ncleanout and 1% in the neighboring house.\n9 Subsequently, Atmos employees removed\nnearby sewer manhole covers to vent the gas from the sewer.\nDuring the emergency response to the fire and natural gas monitoring, other\nAtmos personnel continued working to shut off the flow of gas. They isolated the leak at\n7:58 a.m. by closing two valves on a connected 4-inch main and squeezing off the\ndamaged 2-inch main north of the leak.\n10 They later restored gas service to much of the\narea by squeezing off the 2-inch main south of the leak and reopening the valves on the\n4-inch main. By 8:10 a.m., the second Atmos senior service technician’s CGI readings in\nthe accident home’s sewer cleanout and nearby structures all indicated 0% gas.\n1.2 Atmos\nAtmos is an independent, publicly held natural gas distribution company\nheadquartered in Dallas, Texas. At the time of the accident, it employed about 5,000\npeople across six regional divisions comprising eight US states. Atmos served more than\nthree million customers in over 1,400 communities and operated about 75,000 miles of\ndistribution pipeline and was the largest natural gas distributor in the states of Louisiana,\nMississippi, and Texas.\n8 A CGI is a device used to detect and measure natural gas or other inflammable gases in air.\n9 In air, natural gas is explosive only at concentrations between 5% and 15% by volume.\n10 Squeezing off a pipe is an emergency procedure in which responders compress a pipe with a\nmanual or hydraulic clamp until gas can no longer flow freely.\n5\n\n<<<PAGE 6>>>\n\nPipeline Investigation Report\nPIR-26-03\n1.3 Personnel\nThe first Atmos employee on the scene, who arrived about 5:35 a.m., was a senior\nservice technician. He had 17 years of experience with Atmos, including 11 years in\nconstruction and 5 years in distribution service. His typical daily work involved reading\nmeters and completing service calls.\nThe Atmos crew leader, who arrived on-scene about 6:10 a.m., had 10 years of\nnatural gas experience, 4 of them in construction with Atmos. His typical daily work\ninvolved planning and leading construction activities like service installation, main\ninstallation, and leak repairs in the field.\nThe second Atmos senior service technician, who arrived on-scene about\n7:25 a.m., had 14 years of experience, including 2 years in construction and 12 years in\ndistribution service. His typical daily work involved reading meters, responding to leak\nemergencies, and service orders.\n1.4 Pipeline, Valve, and Valve Box\nThe pipeline involved in this accident was originally installed by another utility in\n1952 and 1960. Atmos acquired it in 2001 along with its other Louisiana assets. The\nmaximum allowable operating pressure in the area was 100 pounds per square inch\ngauge (psig).\n11 The system pressure was 80 psig at 5:02 a.m. on December 2, 2024,\naccording to Atmos records. No Atmos assets were connected to the accident home,\nwhich did not have natural gas service.\nThe valve near the leak was a 2-inch threaded valve. The valve box positioned\nover the valve was a cast iron cylinder 24.75 inches long and varying in diameter along\nits length. At its base, it had a diameter of 8.375 inches, and its wall was flared to create a\nrim about 0.95 inches wide. (See figure 3.) Its date of original installation is unknown.\nThe infrastructure was last excavated on October 9, 2024, when Atmos\ncompleted a project to offset the main to accommodate a storm drain for a new library\nunder construction. During this work, Atmos employees unearthed a section of main,\ngreased and turned the valve, and removed and reinstalled the valve box over the valve.\nAccording to the Atmos senior field construction coordinator involved in the project, the\ntop of the valve box was level with the surrounding grade and marked to identify the gas\nvalve when the work was completed. (See figure 3.)\n11 Pounds per square inch gauge, or psig, indicates the pressure difference between the inside a\ncontainer, like a pipeline or tank, and the ambient environment.\n6\n\n<<<PAGE 7>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 3. Valve box after the accident (left) and October 2024 Google Street View image of valve\nbox cover (right).\nAt the time of the last excavation near the accident valve, Atmos was no longer\ninstalling new cast iron valve boxes and had adopted plastic valve boxes sandwiched\nbetween two pads: a support pad installed below the main and a concrete “base pad” at\nthe grade. The new valve box design has a cutout at the lower edge and rests on the\nsupport pad. Atmos did not have a process or rule for replacing existing cast iron valve\nboxes with the newer design or a written procedure for reinstalling cast iron valve boxes.\nDuring a meeting with the NTSB, the Atmos Vice President of Operations for the\nLouisiana Division Eastern Region said that installing valve boxes in contact with mains\nwas a common practice across Atmos’ Louisiana Division. Later emails from Atmos said\nthat Atmos expected the box structure, rim, and soil to bear loads whenever a valve box\nwas installed level with the surrounding grade. See figure 4 for a comparison of valve\nbox installations.\n7\n\n<<<PAGE 8>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 4. Valve box installations.\nFederal regulations at Title 49 Code of Federal Regulations (CFR)\nPart 192.181(c)(3) require that when a box or enclosure is installed over a valve, “the box\nor enclosure must be installed so as to avoid transmitting external loads to the main.”\n1.5 Examinations and Tests\n1.5.1 Excavation\nAtmos’s on-scene excavation on December 2, 2025, identified a fracture in the\nAvondale Garden Road main near a valve at the eastern edge of the construction site.\nThe main was fractured around most of its circumference, with a thin strip of metal\nremaining at the 12 o’clock position (the top of the pipe) just south of where the main\nthreaded into the valve body. (See figure 5.) Two leak surveys conducted by Atmos\nalong Avondale Garden Road and several nearby streets on December 2 did not identify\nadditional sources of gas.\n8\n\n<<<PAGE 9>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 5. Excavated gas main.\nThe excavation also unearthed the end of an uncapped, 6-inch plastic pipe about\n8 inches from the fracture. (See figure 6.) Investigators sent inspection cameras through\nthis pipe and found that it was a sewer lateral connected to the main sewer system in the\narea but not to any other structure, like a house or business. A series of camera\ninspections identified a continuous path between this uncapped pipe and the accident\nhome.\n9\n\n<<<PAGE 10>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 6. Uncapped pipe near gas main fracture.\n1.5.2 Postaccident Examinations\nThe NTSB recovered the valve box and three sections of main near the fracture for\nexamination in the Materials Laboratory. (See figure 7.) The thin strip of metal shown in\nfigure 5 broke during recovery.\n10\n\n<<<PAGE 11>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 7. Recovered assets.\nThe valve was mostly cylindrical in shape with threaded joints on the north and\nsouth end. The fractured main was threaded about 0.5 inches into the south end of the\nvalve. The outside of the main was coated with coal tar. The geometries of the fracture\nsurfaces appeared to mirror each other, with no missing sections.\nMeasurements of the main’s inside and outside diameter near the fracture found\nan average wall thickness of 0.156 ± 0.005 inches, with a total range (difference between\ngreatest and least measurement) of 0.015 inches. The examination did not find signs of\nsignificant wall thinning. The hardness of the steel near the fracture surface was\nconsistent with carbon steel.\nThe Materials Laboratory removed a section of the fractured main by making a cut\nabout 0.75 inches from the fracture. There was a slight outward bend in the fracture\nsurface near the 12 o’clock position where the thin strip of metal had connected pieces\nof the fractured main before recovery from the scene. (See figure 8.) No other significant\ndeformation was noted in the main near the fracture surface.\n11\n\n<<<PAGE 12>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 8. Sectioned main with fracture surface and outward bend.\nThe Materials Laboratory examined the fracture surface with a field-emission\nscanning electron microscope. The examination identified angled facets associated with\ntransgranular brittle failure: crack growth through the grains of material rather than along\nboundaries between grains. These angled facets are typical of fast crack growth through\nsteel.\nExamination of the valve box found hard black deposits of material at two\nlocations on the bottom rim. (See figure 9.) The deposits were 180° apart around the rim\nof the valve box and resembled the coating on the pipeline itself. Spectroscopic\nexamination of the material identified it as coal tar.\n12\n\n<<<PAGE 13>>>\n\nPipeline Investigation Report\nPIR-26-03\nFigure 9. Black deposits on the valve box before cleaning.\n1.6 Atmos Leak Response Procedures\nAtmos’s leak response procedures in place at the time of the accident are\ndocumented in the 2023 edition of its Service Procedure Manual.12 The 2023\nprocedures direct employees to treat each leak as potentially hazardous until it is\ndetermined to be non-hazardous. If employees identify a hazardous condition, they are\nto undertake “continuing actions” to\n• continue with determination of the hazard,\n• determine the extent of the hazard, and\n• protect life and property.\nSpecific continuing actions include evacuating occupants of affected structures,\nshutting off gas, moving to a safe location, calling 9-1-1 and notifying an Atmos\nsupervisor, eliminating sources of ignition, and establishing a perimeter to restrict entry\nto the affected area. The Service Procedure Manual notes that employees will rely on\n12 The version in place at the time of the accident was dated October 2023. Atmos Energy released an\nupdated version in June 2025.\n13\n\n<<<PAGE 14>>>\n\nPipeline Investigation Report\nPIR-26-03\ntheir “training and experience” when determining the appropriate order for the\ncontinuing actions.\nFor leaks located outside a structure, the Service Procedure Manual directs\nemployees to investigate above ground level first, including the areas over gas lines\naround nearby structures, along other underground utilities such as water and sewer\nlines, and at accessible openings into enclosed or underground spaces such as “sewer\nvents, sewer cleanouts, sewer manholes, storm drains, utility manholes or boxes,\ncrawlspaces, substructures, and the perimeter of potentially involved structures.”\nDetecting gas in or near any of these structures requires taking the continuing actions\ndescribed above.\nAfter completing the surface investigation, employees are to complete a\nsubsurface investigation, including bar-hole testing and testing within accessible\nunderground utilities and the other infrastructure described as part of the surface\ninvestigation, including sewers and storm drains. If gas is detected in any of these\nlocations, employees are to take continuing actions and expand the investigation to\ninclude adjacent structures and properties along the street.\n1.7 Postaccident Actions\nAtmos reported that it provided emergency response training to its own\noperation managers and supervisors throughout early 2025, who then provided\nrefresher training to employees in their local offices. As of its last update in September\n2025, Atmos reported that these trainings were substantially complete. Atmos also\nreported that it started providing in-person leak response training to the East and West\nJefferson Parish Fire Departments in June 2025.\nAtmos also replaced the gas main and service lines along Avondale Garden Road\nand installed a plastic valve box.\nAnalysis\nThe explosion and fire occurred after natural gas leaked from a fractured buried\nmain, migrated through an uncapped underground sewer lateral, entered the accident\nhome, and reached an explosive concentration near an unknown ignition source. The\ninvestigation did not identify issues with gas pressures in the area of the leak or the\ntimeliness or efficacy of the local emergency response agencies.\nPostaccident bar-hole testing and excavations found only one source of natural\ngas: a leak in the gas main near a valve box on the eastern edge of the construction site.\nOn-site examinations of the main found that it was fractured around most of its\ncircumference with a thin strip of metal at the top (12 o’clock position) joining the\n14\n\n<<<PAGE 15>>>\n\nPipeline Investigation Report\nPIR-26-03\nsouthern section of pipe to the section still threaded into the valve body. This indicates\ntension—a stretching force—at the bottom of the pipe along its long axis. Tension along\nthe bottom of the pipe is consistent with a bending stress created by an external\ndownward force. Based on information provided to Atmos by the construction\nsuperintendent, a cement truck ran over a valve box at the leak’s location immediately\nbefore he heard and smelled natural gas being released. The investigation did not\nidentify another plausible external force that could have damaged the main.\nThe Materials Laboratory examination of the main found fracture characteristics\ntypical of fast crack growth and no signs of significant corrosion or preexisting structural\ndamage that could have contributed to the failure. The fracture was therefore consistent\nwith a sudden application of force by the valve box to the main.\nBased on the fracture’s location, timing, and fast-cracking characteristics, the valve\nbox transmitted part of the cement truck’s weight to the gas main, causing the main to\nfracture and leak. Examination of the gas main and valve box involved in this accident\nfound coal tar coating the main and deposited on the bottom edge of the valve box. This\nindicates that the valve box was in contact with the main. The presence of coal tar alone\ndoes not indicate when the contact occurred, but the evidence is consistent with the\nvalve box being installed in contact with the main and therefore able transmit the cement\ntruck’s weight directly to the main near the fracture’s location.\nFederal regulations at 49 CFR 192.181(c)(3) require that valve boxes not be\ninstalled in a manner that transmits external loads to mains, and valve boxes are normally\ninstalled with a buffer of soil or other protection between the valve box and the assets\nimmediately below. For example, Atmos’s newer valve boxes are installed with support\nand base pads to prevent load transmission. However, Atmos was not actively replacing\ncast iron valve boxes with this newer design. Further, the maintenance crew that\nremoved and reinstalled the valve box about 2 months before the accident did not have\na specific standard to follow for reinstalling cast iron valve boxes other than an\nexpectation that the top of the valve box be level with the grade. The lack of a standard\nlikely led to the common reinstallation of valve boxes in contact with mains, as described\nby an Atmos vice president of operations.\nIf Atmos had adopted either a standard for safely installing cast iron valve boxes\nor a policy of replacing cast iron valve boxes with the newer design, the protective buffer\nof soil or support pad would have reduced the load transmitted to the pipe on the day of\nthe accident. There is not enough evidence to determine whether a buffer or pad would\nhave prevented the accident, but it would have made the infrastructure more resilient.\nAtmos has not reported making changes to its valve box installation practices.\nAfter the main fractured, gas propagated undetected through an uncapped\nunderground sewer lateral into the sewer system and then into the accident home,\n15\n\n<<<PAGE 16>>>\n\nPipeline Investigation Report\nPIR-26-03\nwhere it reached an explosive concentration. The gas in the sewers remained\nundetected because Atmos personnel did not test the atmosphere in the sewers prior to\nthe explosion. For about 35 minutes, most of the time between the initial leak and the\nexplosion, there was only one Atmos employee on the scene: an experienced senior\nservice technician. He was equipped with a CGI and checked nearby storm drains for the\npresence of gas, which was one step in Atmos’s subsurface leak investigation procedure.\nDuring his interview with the NTSB, he described planning to check the sewers, another\nrequired step, but said that he had already confirmed that there was no threat to life or\nproperty. His activities after checking the storm drains are also consistent with a belief\nthat he had finished assessing the risk posed by the leak: he switched to the non-safety-\ncritical work of recording billing information for the damage.\nThe investigation did not find evidence of a natural gas alarm in the accident\nhome, which did not have gas service but was still impacted by a leak from a gas main. It\nis likely that a natural gas alarm would have provided the home’s occupants with warning\nof accumulating natural gas and given them an opportunity to evacuate before the\nexplosion.\nThe NTSB has advocated wider installation and use of natural gas alarms for\nnearly 50 years, including following the investigation into a pair of 2024 home explosions\nin Jackson, Mississippi, that involved Atmos assets. As a result of that investigation, the\nNTSB reiterated a recommendation to the 50 states, the Commonwealth of Puerto Rico,\nand the District of Columbia:\nRequire the installation of natural gas alarms that meet the specifications of\nNational Fire Protection Association 715 in businesses, residences, and\nother buildings where people congregate that could be affected by a\nnatural gas leak. (P-25-5)13\nThe NTSB also recommended that Atmos “develop and implement a program\nthat makes natural gas alarms available to members of the public who reside in its\ndistribution areas” (P-26-10).\n14\nProbable Cause\nThe National Transportation Safety Board determines that the probable cause of\nthe Avondale, Louisiana, home explosion was the release and underground migration of\nnatural gas from a gas main that failed when a cement truck drove over a valve box that\n13 See CAROL for the complete history and current status of this recommendation.\n14 See CAROL for the complete history and current status of this recommendation.\n16\n\n<<<PAGE 17>>>\n\nPipeline Investigation Report\nPIR-26-03\nthe Atmos Energy Corporation installed in contact with the gas main; the valve box\ntransmitted the truck’s weight to the main and fractured it. Contributing to the severity of\nthe accident was the Atmos Energy Corporation’s failure to identify the underground\nmigration of gas during its leak investigation and to recognize the need to evacuate\nstructures outside the immediate area of the leak.\nLessons Learned\nFederal regulations require that valve boxes be installed such that they do not\ntransmit external loads to buried natural gas assets, as occurred in the Avondale\naccident. Natural gas operators can improve safety by making sure that employees have\nthe tools, knowledge, and clear procedures they need to comply with federal regulations\nwhen installing or maintaining valve boxes, and by taking every opportunity to update\nlegacy valve boxes with modern designs and materials.\nThe unidentified danger of underground gas migration in the Avondale accident\nillustrates the importance of completing a thorough leak investigation before shifting to\nnon-safety-critical tasks. Operators can protect the quality of leak investigations through\nmeans such as oversight, regular training, and work aids to ensure employees know and\nfollow leak response procedures.\nThis accident also underscores the value of natural gas alarms even in buildings\nthat do not have natural gas service but are located near natural gas assets. Natural gas\nalarms provide both early warning of dangerous gas concentrations and a last line of\ndefense when a leak investigation fails to identify a hazard. Further information about\nnatural gas alarms is available on the NTSB website.\n17\n\n<<<PAGE 18>>>\n\nPipeline Investigation Report\nPIR-26-03\nThe NTSB is an independent federal agency charged by Congress with\ninvestigating every civil aviation accident in the United States and significant events in the\nother modes of transportation—railroad, transit, highway, marine, pipeline, and\ncommercial space. We determine the probable causes of the accidents and events we\ninvestigate and issue safety recommendations aimed at preventing future occurrences. In\naddition, we conduct transportation safety research studies and offer information and\nother assistance to family members and survivors for each accident or event we\ninvestigate. We also serve as the appellate authority for enforcement actions involving\naviation and mariner certificates issued by the Federal Aviation Administration (FAA) and\nUS Coast Guard, and we adjudicate appeals of civil penalty actions taken by the FAA.\nThe NTSB does not assign fault or blame for an accident or incident; rather, as\nspecified by NTSB regulation, “accident/incident investigations are fact-finding\nproceedings with no formal issues and no adverse parties … and are not conducted for\nthe purpose of determining the rights or liabilities of any person” (Title 49 Code of\nFederal Regulations section 831.4). Assignment of fault or legal liability is not relevant to\nthe NTSB’s statutory mission to improve transportation safety by investigating accidents\nand incidents and issuing safety recommendations. In addition, statutory language\nprohibits the admission into evidence or use of any part of an NTSB report related to an\naccident in a civil action for damages resulting from a matter mentioned in the report\n(Title 49 United States Code section 1154(b)).\nFor more detailed background information on this report, visit the NTSB Case\nAnalysis and Reporting Online (CAROL) website and search for NTSB accident ID\nPLD25FR002. Recent publications are available in their entirety on the NTSB website.\nOther information about available publications also may be obtained from the website or\nby contacting—\nNational Transportation Safety Board\nRecords Management Division, CIO-40\n490 L’Enfant Plaza, SW\nWashington, DC 20594\n(800) 877-6799 or (202) 314-6551\n18","truncated":false,"body_characters":33534}