{"operation":"document","citation":"PLD24FR003","title":"Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires","source_type":"incident","agency":"National Transportation Safety Board","status":"current","official":true,"published_on":"2026-03-26","effective_on":"2024-01-24","summary":"Accident. in Jackson, MS, USA. on 2024-01-24. Atmos Energy Mississippi. Leak/explosion/fire","machine_formats":{"json":"https://regulus.evalyn.ai/document/ntsb-case-pld24fr003.json","markdown":"https://regulus.evalyn.ai/document/ntsb-case-pld24fr003.md"},"app_url":"https://regulus.evalyn.ai/document/ntsb-case-pld24fr003","source_url":"https://www.ntsb.gov/investigations/Pages/PLD24FR003.aspx","body":"NTSB investigation PLD24FR003.\n\nEvent Type: Accident\n\nEvent Date: 2024-01-24\n\nEvent City: Jackson\n\nEvent State Or Region: MS\n\nEvent Country: USA\n\nPipeline Operator: Atmos Energy Mississippi\n\nPipeline Type: Distribution\n\nAccident Type: Leak/explosion/fire\n\nCompletion Status: Completed\n\nReport Number: PIR2601\n\nReport Date: 2026-03-12\n\nProbable cause: The National Transportation Safety Board determines that the probable cause of the two explosions at two separate homes in Jackson, Mississippi, was the service-line pipes partially pulling out of the compression couplings, likely because of soil movement (shrinking and swelling), creating natural gas leaks that Atmos Energy Corporation identified and left unrepaired for at least 8 weeks, which enabled gas to migrate to the nearby homes and ignite. Contributing to Atmos Energy Corporation’s failure to prevent the accidents were the operator’s: (1) insufficient leak management program, which did not determine appropriate monitoring timelines for leaks in adverse-soil conditions; (2) ineffective public awareness program, which did not adequately educate the public or emergency response officials on how to respond to a suspected natural gas leak; and (3) inadequate integrity management program, which did not appropriately assess and address risk in its Mississippi Division pipeline system.\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\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Management\n\nFinding Tier3Name: Policy/procedure\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Management - Policy/procedure - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Oversight\n\nFinding Modifier Name: Pipeline operator\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Oversight - Pipeline operator\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Oversight\n\nFinding Modifier Name: Federal agency\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Oversight - Federal agency\n\nFinding Tier1Name: Organizational\n\nFinding Tier2Name: Support/oversight/monitoring\n\nFinding Tier3Name: Enforcement\n\nFinding Modifier Name: Federal agency\n\nFinding Report Text: Organizational - Support/oversight/monitoring - Enforcement - Federal agency\n\nFinding Tier1Name: Environment/Infrastructure\n\nFinding Tier2Name: Physical environment\n\nFinding Tier3Name: Soil\n\nFinding Modifier Name: Awareness of condition\n\nFinding Report Text: Environment/Infrastructure - Physical environment - Soil - Awareness of condition\n\nFinding Tier1Name: Pipeline\n\nFinding Tier2Name: Pipline systems/equipment\n\nFinding Tier3Name: Fittings\n\nFinding Modifier Name: Failure\n\nFinding Report Text: Pipeline - Pipline systems/equipment - Fittings - Failure\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 January 24, 2024, about 8:14 a.m. local time, natural gas leaked from a compression coupling into a home on Bristol Boulevard in Jackson, Mississippi, causing an explosion and fire that resulted in one fatality, one injury, and a destroyed home. Three days later, on January 27, 2024, about 4:34 a.m., natural gas leaked from a compression coupling into a home on Shalimar Drive, about 0.7 miles from the first explosion, causing an explosion and fire that destroyed two homes. (A compression coupling is a pipeline component that joins and seals two pipes together. It is typically belowground and connects a service-line pipe to a main-line pipe.)\n\nWhat We Found\nWe determined that the probable cause of the two explosions at two separate homes in Jackson, Mississippi, was Atmos Energy Corporation’s inadequate leak management program, which allowed for known natural gas leaks, from service-line pipes that had partially pulled out of compression couplings due to soil movement, to be left unrepaired for at least 8 weeks, resulting in gas leaking from the compression couplings and then migrating to the nearby homes and igniting. Contributing to the explosions was Atmos Energy Corporation’s inadequate integrity management program, which did not appropriately assess and address risk in its pipeline system. Also contributing was an ineffective public awareness program, which did not adequately educate the public or emergency response officials on how to respond to a suspected natural gas leak.\n\nWhat We Recommended\nAs a result of this investigation, we made the following new safety recommendations. Read the complete list and status of recommendations.\n\nTo the Department of Transportation Office of Inspector General: Audit the Pipeline and Hazardous Materials Safety Administration’s ongoing joint assessment of Atmos Energy Corporation (with the eight state partners that regulate Atmos Energy Corporation’s facilities), including a review of Atmos Energy Corporation’s approach to the safety management of its pipeline and how it applies lessons learned across all its operating divisions. (P-26-1)\n\nTo the Pipeline and Hazardous Materials Safety Administration: Issue an advisory bulletin urging operators to adopt probabilistic risk models for distribution integrity management where appropriate. (P-26-2)\n\nTo Atmos Energy Corporation:\nDevelop and implement a program to locate and replace all mechanical couplings and mechanical joints located in expansive soils that are not resistant to pipe pullout with couplings and joints developed specifically for those conditions. The program should establish and make public the project milestones and timeline. (P-26-3)\nUpdate your companywide leak management program procedures to require weekly monitoring of nonhazardous (grade 2 or grade 3) belowground leaks identified in locations with adverse-soil conditions (such as water-saturated soil, flooding, drought, frozen ground, or settlement). (P-26-4)\nAfter completing the action described in P-26-4, implement a training program to maintain employee and contractor proficiency on the updated procedures. (P-26-5)\nDevelop and implement a program to provide more frequent training to emergency response officials in all the distribution areas that you serve, including training on how to respond to natural gas-leak calls, and monitor the program for effectiveness. (P-26-6)\nRequire your technicians who identify but do not repair a belowground natural gas leak to immediately notify people near the unrepaired leak that (1) the hazard potential of a leak can change over time, and (2) they should evacuate and then call 9-1-1 and Atmos Energy Corporation every time they smell natural gas odorant. (P-26-7)\nDevelop and implement a program to proactively identify and collect missing service-line information for all your operating divisions. The program should (1) identify one or more methods for gaining additional system data and (2) establish and make public the milestones and timeline for acquiring the unknown system data. (P-26-8)\nTransition from a relative-risk model to a probabilistic distribution integrity management risk model. (P-26-9)\nDevelop and implement a program that makes natural gas alarms available to members of the public who reside in your distribution areas. (P-26-10)\n\nWe reiterated the following safety recommendations\n\nTo the Pipeline and Hazardous Material Safety Administration:\nEvaluate industry’s implementation of the gas distribution pipeline integrity management requirements and develop updated guidance for improving their effectiveness. The evaluation should specifically consider factors that may increase the likelihood of failure such as age, increase the overall risk (including factors that simultaneously increase the likelihood and consequence of failure), and limit the effectiveness of leak management programs. (P-21-2)\nIdentify effective means for natural gas distribution pipeline operators to communicate with people who live, work, or congregate within the coverage area of a natural gas distribution pipeline system and implement a plan to help operators drive continuous improvement in public awareness of natural gas safety. (P-25-3)\nTo 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)\n\nPIR-26-01\n<<<PAGE 1>>>\n\nMarch 12, 2026 Pipeline Investigation Report PIR-26-01\nAtmos Energy Corporation Natural\nGas-Fueled Home Explosions and Fires\nJackson, Mississippi\nJanuary 24, 2024, and January 27, 2024\nAbstract: This report discusses the January 2024 natural gas-fueled explosions and\nfires at two separate homes in Jackson, Mississippi, which occurred 3 days apart,\ncollectively resulting in one injury, one fatality, and three destroyed homes. Safety\nissues identified in this report include compression coupling leaks, insufficient leak\nmanagement program, inadequate distribution integrity management program,\nineffective public awareness program, and absence of natural gas detection alarms in\nbuildings. As part of this investigation, the National Transportation Safety Board\nissued safety recommendations to the Department of Transportation Office of\nInspector General, the Pipeline and Hazardous Materials Safety Administration, and\nAtmos Energy Corporation and reiterated recommendations to the Pipeline and\nHazardous Materials Safety Administration and to 50 states, the Commonwealth of\nPuerto Rico, and the District of Columbia.\n\n<<<PAGE 2>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nContents\nContents ................................................................................................................. i\nFigures ..................................................................................................................iv\nTables ....................................................................................................................vi\nAcronyms and Abbreviations ...............................................................................vii\nExecutive Summary ............................................................................................. viii\nWhat Happened............................................................................................................. viii\nWhat We Found ............................................................................................................. viii\nWhat We Recommended ............................................................................................... ix\n1 Factual Information ......................................................................................... 1\n1.1 The Accidents ........................................................................................................... 1\n1.1.1 Bristol Boulevard ............................................................................................. 3\n1.1.2 Shalimar Drive .................................................................................................. 9\n1.2 Emergency Response ............................................................................................ 13\n1.2.1 Bristol Boulevard ........................................................................................... 13\n1.2.2 Shalimar Drive ................................................................................................ 14\n1.3 Weather ................................................................................................................... 15\n1.3.1 Bristol Boulevard ........................................................................................... 15\n1.3.2 Shalimar Drive ................................................................................................ 16\n1.4 Expansive Soil ......................................................................................................... 16\n1.5 Dresser Style 90 Compression Coupling ............................................................ 19\n1.6 Examinations and Testing ..................................................................................... 20\n1.6.1 On-Scene Examinations and Testing .......................................................... 20\n1.6.2 Laboratory Examinations and Testing ........................................................ 27\n1.7 Regulations and Advisory Bulletins ..................................................................... 35\n1.7.1 Regulations ..................................................................................................... 35\n1.7.2 Advisories and Reports ................................................................................. 37\n1.8 Atmos Energy Corporation ................................................................................... 38\n1.8.1 Company Overview ....................................................................................... 38\n1.8.2 Pipeline Safety Management Systems ........................................................ 39\ni\n\n<<<PAGE 3>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\n1.8.3 Safety Performance ....................................................................................... 40\n1.9 Procedures and Policies ........................................................................................ 40\n1.9.1 Leak Management ......................................................................................... 40\n1.9.2 Public Awareness ........................................................................................... 48\n1.9.3 Distribution Integrity Management ............................................................. 52\n1.10Relevant Atmos Accidents .................................................................................... 56\n1.11State and Federal Oversight ................................................................................. 58\n1.12Postaccident Actions ............................................................................................. 58\n1.12.1 Pipeline and Hazardous Materials Safety Administration ................. 58\n1.12.2 Mississippi Public Service Commission .............................................. 59\n1.12.3 Atmos Energy Corporation .................................................................. 59\n2 Analysis ......................................................................................................... 62\n2.1 Introduction ............................................................................................................ 62\n2.2 Compression Coupling Leaks .............................................................................. 63\n2.3 Insufficient Leak Management Program ............................................................. 68\n2.3.1 Leak Repair and Leak Reevaluation ............................................................ 68\n2.3.2 Leak Monitoring ............................................................................................. 68\n2.4 Ineffective Public Awareness Program ................................................................ 70\n2.4.1 Public Awareness Program Effectiveness ................................................... 70\n2.4.2 Odor Complaints ........................................................................................... 74\n2.5 Inadequate Distribution Integrity Management Program ................................ 75\n2.5.1 System Data .................................................................................................... 75\n2.5.2 Risk Model ...................................................................................................... 76\n2.6 Absence of Natural Gas Detection Alarms in Buildings .................................... 81\n3 Conclusions ................................................................................................... 84\n3.1 Findings ................................................................................................................... 84\n3.2 Probable Cause ...................................................................................................... 85\n4 Recommendations ........................................................................................ 86\n4.1 New Recommendations ........................................................................................ 86\n4.2 Previously Issued Recommendations Reiterated in This Report ...................... 87\nAppendixes ......................................................................................................... 89\nii\n\n<<<PAGE 4>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nAppendix A: Investigation ............................................................................................ 89\nAppendix B: Consolidated Recommendation Information ..................................... 90\nReferences........................................................................................................... 94\niii\n\n<<<PAGE 5>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nFigures\nFigure 1. Map and photographs of the accident locations. (Courtesy of Google Earth,\nthe Pipeline and Hazardous Materials Safety Administration, and the Mississippi\nPublic Service Commission [clockwise from the top].) ...................................................... 2\nFigure 2. The Bristol Boulevard accident home before the explosion. (Courtesy of\nGoogle Maps.) ........................................................................................................................ 4\nFigure 3. The Bristol Boulevard accident neighborhood. ................................................. 5\nFigure 4. Aerial photograph of the Bristol Boulevard accident home after the\nexplosion and fire. (Courtesy of Atmos.) ............................................................................. 8\nFigure 5. The Shalimar Drive accident home before the explosion. (Courtesy of\nGoogle Maps.) ...................................................................................................................... 10\nFigure 6. The Shalimar Drive accident neighborhood. ................................................... 11\nFigure 7. The Shalimar Drive accident home (left) and the Shalimar Drive affected\nhome (right) after the explosion and fires. (Courtesy of the Mississippi Public Service\nCommission.) ........................................................................................................................ 12\nFigure 8. US expansive soil map overlaid with Atmos’s headquarters (starred) and\nregional divisions. (Courtesy of the US Geological Survey and Atmos with NTSB\nannotations.) .......................................................................................................................... 17\nFigure 9. A Dresser Style 90 compression coupling. ....................................................... 20\nFigure 10. Postaccident bar-hole testing and open-air testing conducted at\nBristol Boulevard on January 24, 2024, about 12:42 p.m. .............................................. 22\nFigure 11. Postaccident bar-hole testing and open-air testing conducted at\nBristol Boulevard on January 29, 2024, about 9:15 a.m. ................................................ 23\nFigure 12. Postaccident bar-hole testing and open-air testing conducted at\nShalimar Drive on January 27, 2024, about 5:30 a.m. ..................................................... 25\nFigure 13. Postaccident bar-hole testing and open-air testing conducted at\nShalimar Drive on January 29, 2024, about 9:40 a.m. ..................................................... 26\nFigure 14. The Bristol Boulevard natural gas pipeline assembly. .................................. 28\nFigure 15. Scratches on the upstream end of the service line at Bristol Boulevard..... 29\nFigure 16. Excavation photograph of the copper-water pipeline and the service line\nnear the Bristol Boulevard accident location. (Courtesy of Atmos.) .............................. 30\nFigure 17. The Shalimar Drive natural gas pipeline assembly. ....................................... 32\nFigure 18. Scratches on the upstream end of the service line at Shalimar Drive. ........ 33\nFigure 19. The Shalimar Drive service-line pipe and gasket. ......................................... 34\niv\n\n<<<PAGE 6>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nFigure 20. Map of hazardous leaks within a 5-mile radius of Jackson that Atmos\nrepaired in 2023. (Courtesy of ESRI ArcGIS and Atmos with NTSB annotations.) ....... 41\nFigure 21. Map of open leaks within a 5-mile radius of Jackson on January 24, 2024,\nincluding leaks that later met criteria for higher grade leaks. (Courtesy of ESRI ArcGIS\nand Atmos with NTSB annotations.) ................................................................................... 43\nFigure 22. Map of the Atmos risk model’s high-risk grids in Jackson as of January 24,\n2024. (Courtesy of Atmos with NTSB annotations.) ......................................................... 55\nFigure 23. Map of hazardous leaks within a 5-mile radius of Jackson that Atmos\nrepaired in 2023 overlaid with Atmos high-risk grids current on that date. (Courtesy of\nESRI ArcGIS and Atmos with NTSB annotations.) ............................................................. 77\nFigure 24. Map of open, nonhazardous leaks within a 5-mile radius of Jackson as of\nJanuary 24, 2024, including leaks that later met criteria for higher grade leaks,\noverlaid with Atmos high-risk grids current on that date. (Courtesy of ESRI ArcGIS and\nAtmos with NTSB annotations.) .......................................................................................... 79\nv\n\n<<<PAGE 7>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nTables\nTable 1. Timeline of Bristol Boulevard accident events. .................................................... 9\nTable 2. Timeline of Shalimar Drive accident events. ...................................................... 12\nTable 3. Atmos leak classification procedures. ................................................................. 46\nvi\n\n<<<PAGE 8>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nAcronyms and Abbreviations\nAbbreviation Name\nASCE\nCFR\nGPTC\nJFD\nMS PSC\nMSU\nMAFES\nNTSB\nO&M\nPHMSA\npsig\nPSMS\nSME\nAmerican Society of Civil Engineers\nCode of Federal Regulations\nGas Piping Technology Committee\nJackson Fire Department\nMississippi Public Service Commission\nMississippi State University\nMississippi Agricultural and Forestry Experiment Station\nNational Transportation Safety Board\noperations and maintenance\nPipeline and Hazardous Materials Safety Administration\npounds per square inch, gauge\nPipeline Safety Management Systems\nsubject matter expert\nvii\n\n<<<PAGE 9>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nExecutive Summary\nWhat Happened\nOn January 24, 2024, about 8:14 a.m. local time, natural gas leaked from a\ncompression coupling into a home on Bristol Boulevard in Jackson, Mississippi,\ncausing an explosion and fire that resulted in one fatality, one injury, and a destroyed\nhome. Three days later, on January 27, 2024, about 4:34 a.m., natural gas leaked\nfrom a compression coupling into a home on Shalimar Drive, about 0.7 miles from\nthe first explosion, causing an explosion and fire that destroyed two homes.\n(A compression coupling is a pipeline component that joins and seals two pipes\ntogether. It is typically belowground and connects a service-line pipe to a main-line\npipe.)\nWhat We Found\nWe found that near the accident homes, natural gas leaked from service-line\npipes that had partially pulled out of compression couplings and migrated through\nthe ground and into the homes where it fueled the explosions. The leaks near the\naccident homes were the result of expansive clay soil movement that caused the\nservice-line pipes at both locations to, over time, partially pull out of the compression\ncouplings. For both accidents, Atmos Energy Corporation (Atmos) leak surveys\ndetected belowground leaks weeks before the explosion and classified them as\nnonhazardous. This nonhazardous classification meant that Atmos would not repair\nthe leaks immediately. Atmos did not have companywide leak management\nprocedures requiring employees to frequently monitor open, belowground natural\ngas leaks located in adverse-soil conditions, which existed in Jackson, Mississippi, at\nthe time of the two accidents. As a result, the accident leaks became hazardous\nbefore Atmos repaired them.\nSeveral people in the two accident neighborhoods smelled natural gas\nodorant and were unaware of pipeline safety guidance to evacuate and then\nimmediately report the smell by calling 9-1-1 and the gas company. In the accidents\nin Jackson, Mississippi, and in several natural gas accidents that the NTSB has\ninvestigated, the operator’s public awareness program was ineffective at educating\nthe public on how to safely respond to the smell of natural gas odorant. Atmos’s\nineffective communications regarding the need to report any smell of natural gas\nodorant inhibited necessary reporting from residents who continued to smell natural\ngas odorant in and near their homes. In addition, in the two Jackson accidents and in\nprevious Atmos accidents in Dallas, Texas, and Avondale, Louisiana, Atmos missed an\nviii\n\n<<<PAGE 10>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nopportunity to effectively educate and prepare emergency response officials in its\nservice areas to address natural gas emergencies.\nAtmos’s failure to gather relevant information about its service-line records\nprevented it from effectively assessing the risk to its assets. In addition, Atmos’s\ndistribution integrity management program did not effectively identify and then\nmitigate the risks to its system. Also, had a natural gas alarm been installed inside the\nBristol Boulevard accident home, it could have alerted occupants that natural gas was\npresent, prompting them to evacuate and report the leak, making Atmos aware that\nthe leak had likely worsened and required corrective action.\nThe National Transportation Safety Board determines that the probable cause\nof the two explosions at two separate homes in Jackson, Mississippi, was Atmos\nEnergy Corporation’s inadequate leak management program, which allowed for\nknown natural gas leaks, from service-line pipes that had partially pulled out of\ncompression couplings due to soil movement, to be left unrepaired for at least\n8 weeks, resulting in gas leaking from the compression couplings and then migrating\nto the nearby homes and igniting. Contributing to the explosions was Atmos Energy\nCorporation’s inadequate integrity management program, which did not\nappropriately assess and address risk in its pipeline system. Also contributing was an\nineffective public awareness program, which did not adequately educate the public\nor emergency response officials on how to respond to a suspected natural gas leak.\nWhat We Recommended\nAs a result of this investigation, we issued 10 new safety recommendations and\nreiterated 3 recommendations. We recommended that the Department of\nTransportation Office of Inspector General audit the Pipeline and Hazardous\nMaterials Safety Administration’s ongoing joint assessment of Atmos Energy\nCorporation. We recommended that the Pipeline and Hazardous Materials Safety\nAdministration issue an advisory bulletin urging operators to adopt probabilistic risk\nmodels. We recommended that Atmos:\n• Locate and replace all mechanical couplings and mechanical joints in\nexpansive soils that are not resistant to pipe pullout.\n• Require weekly monitoring of nonhazardous belowground leaks\nidentified in locations with adverse-soil conditions.\n• After updating its leak monitoring procedures to address leaks in\nadverse-soil conditions, train its technicians.\nix\n\n<<<PAGE 11>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\n• Train emergency response officials more frequently and monitor the\neffectiveness of the training.\n• Require technicians to immediately notify people near an unrepaired\nleak that the hazard potential of a leak can change over time, and that\nthey should evacuate the area and then call 9-1-1 and Atmos every time\nthey smell natural gas odorant.\n• Proactively identify and collect missing service-line information for all its\noperating divisions.\n• Transition from a relative-risk model to a probabilistic risk model.\n• Make natural gas alarms available to members of the public who live in\nits distribution areas.\nWe reiterated two recommendations to the Pipeline and Hazardous Materials\nSafety Administration. The first was a 2025 recommendation to identify effective\nmeans for natural gas distribution pipeline operators to communicate with people\nwithin the coverage area of a natural gas distribution pipeline system and help\noperators improve public awareness of natural gas safety. The second was a 2021\nrecommendation to evaluate industry implementation of gas distribution pipeline\nintegrity management requirements and develop updated guidance for improving\nthe effectiveness of the requirements. We also reiterated a 2025 recommendation to\nthe 50 States, Puerto Rico, and the District of Columbia to require natural gas alarms\nin businesses, residences, and other buildings where people congregate.\nx\n\n<<<PAGE 12>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\n1 Factual Information\n1.1 The Accidents\nOn January 24, 2024, about 8:14 a.m. local time, a home explosion and fire\noccurred at 185 Bristol Boulevard (Bristol Boulevard accident home) in Jackson,\nMississippi, resulting in one fatality, one injury, and a destroyed home.1 Three days\nlater, on January 27, 2024, about 4:34 a.m., approximately 0.7 miles southeast of the\nfirst explosion, another home explosion and fire occurred at 1146 Shalimar Drive\n(Shalimar Drive accident home), and the fire spread to a neighboring home, resulting\nin two destroyed homes.2 (See figure 1.) At the time of both accidents, weather\nconditions included light to heavy rain, and the temperature was about 60˚F.\n1 All times are local unless otherwise noted.\n2 (a) The Shalimar Drive accident did not result in any injuries. (b) Visit http://www.ntsb.gov to\nfind additional information in the public docket for this National Transportation Safety Board (NTSB)\naccident investigation (case number PLD24FR003). Use the CAROL Query to search safety\nrecommendations and investigations.\n1\n\n<<<PAGE 13>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nFigure 1. Map and photographs of the accident locations. (Courtesy of Google Earth, the\nPipeline and Hazardous Materials Safety Administration, and the Mississippi Public Service\nCommission [clockwise from the top].)\nAtmos Energy Corporation (Atmos) owned and operated natural gas pipeline\nassets near the Bristol Boulevard accident home and the Shalimar Drive accident\nhome.\n3 Atmos distributed natural gas to both homes with 2-inch diameter\ncoated-steel gas mains that ran in front of the homes.4 Service lines to individual\nhomes were connected with 3⁄4-inch steel service tees that were welded on the main\n3 (a) See section 1.8 for more information on Atmos. (b) This report uses the term assets to refer\nto the specific elements of a pipeline distribution system.\n4 (a) A gas main (or main line), which is typically belowground, is a natural gas distribution\npipeline that serves as a common source of supply for more than one service line. (b) The main near\nthe Bristol Boulevard accident home was installed in 1967; the main near the Shalimar Drive accident\nhome was installed in 1962.\n2\n\n<<<PAGE 14>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nand joined to a 3⁄4-inch steel service line.5 Dresser Style 90 seal-only compression\ncouplings made the mechanical joints that connected the service lines to the service\ntees. (This report’s references to Dresser Style 90 compression couplings refer to the\nseal-only design unless otherwise noted. The seal-only design is not configured to\nresist pipe pullout, meaning it is not designed to hold the pipe in place. Other\nversions of the Dresser Style 90 compression coupling include a clamping design that\nresists pipe pullout; however, the seal-only design does not.) (See section 1.5 for\nmore information on Dresser Style 90 compression couplings.) Around the time of\nthe two accidents, the gas mains near both homes were operating below the\nmaximum allowable operating pressure of 40 pounds per square inch, gauge (psig).\n6\n1.1.1 Bristol Boulevard\nThe Bristol Boulevard accident home, built in 1972, was a single-story,\nsingle-family, wood-framed structure with masonry construction on a concrete\nfoundation. (See figure 2.) The home was constructed on soil composed of Yazoo\nclay, an expansive clay prone to movement (shrinking and swelling) during cycles of\ndry and wet weather.\n7 (See section 1.4 for more information on expansive soil.)\n5 (a) A service line, which is typically belowground except when it is near a gas meter, is a\npipeline that transports natural gas (or another commodity) to a customer. (b) The NTSB could not\nconfirm the service-line installation dates (Atmos reported that it did not have the installation records\nfor the service lines at the two accident homes.); however, the NTSB determined that the accident\ncompression couplings contained components manufactured in or before 1963. (c) Compression\ncouplings are a type of mechanical fitting (or mechanical coupling) used to join and pressure seal two\npipes together without requiring soldering, welding, or threading. (d) A service tee, which is typically\nbelowground, creates a branch connection that enables a service line to connect to a main.\n6 (a) At the time of the Bristol Boulevard accident, the main near the Bristol Boulevard accident\nhome was estimated to be operating about 36.5 psig. At the time of the Shalimar Drive accident, the\nmain near the Shalimar Drive accident home was estimated to be operating about 36.6 psig. The NTSB\nalso reviewed the operating pressure histories for both accident locations, and they were below the\nmaximum allowable operating pressure. (b) Natural gas distribution operators typically conduct\npipeline operations slightly below the maximum allowable operating pressure to allow for potential\npressure fluctuations.\n7 (a) Soil is composed of sand, silt, and clay. (b) Expansive soil is soil that undergoes significant\nvolume changes—shrinking when dry and swelling when wet—because of its high clay content.\n3\n\n<<<PAGE 15>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nFigure 2. The Bristol Boulevard accident home before the explosion. (Courtesy of\nGoogle Maps.)\nWhile Atmos provided natural gas service to the Bristol Boulevard accident\nhome, it did not provide gas service to all the homes in the neighborhood, including\nthe home at 175 Bristol Boulevard (Bristol Boulevard affected home), at which,\npostaccident, Atmos bar-hole testing detected explosive levels of natural gas.8 Figure\n3 shows the accident neighborhood, indicating the homes that had natural gas\nservice and those that did not. It also shows the accident leak location, which will be\ndiscussed in section 1.6.1.1.2.\n8 Bar-hole testing describes a gas measurement technique in which a technician makes a small\ndiameter hole in the ground with a steel bar, inserts a probe into the hole, and obtains a gas\nmeasurement. Technicians review bar-hole readings to determine the extent of natural gas in the\nground in the tested area. (See section 1.6 for more information on this and other accident-related\nexaminations and testing.)\n4\n\n<<<PAGE 16>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nFigure 3. The Bristol Boulevard accident neighborhood.\nAbout 9 weeks before the accident on Bristol Boulevard, on\nNovember 17, 2023, after a routine, periodic mobile leak survey detected an\nindication of natural gas, an Atmos contractor, a survey technician, investigated the\nindication by conducting a walking leak survey near the Bristol Boulevard accident\nhome.\n9 (Atmos conducted walking leak surveys in response to mobile leak surveys\nthat detected indications of natural gas.) The technician located a leak and classified\nthe leak as grade 2, meaning he determined the leak was nonhazardous at that time\nbut noted that it required a scheduled repair because it could become hazardous in\n9 (a) Atmos’s procedures required it to conduct mobile leak surveys every 5 years. (b) In a\nmobile leak survey, the pipeline operator deploys a vehicle (such as a truck or an aircraft) with\nmobile-data collection equipment to detect methane concentrations (the primary component of\nnatural gas is methane). (c) In a walking leak survey, a technician walks near or over gas mains and\nservice lines and up to each meter set (the gas meter and associated components) in the survey area\nwhile carrying a handheld leak-detection instrument. (d) Federal regulations in\nTitle 49 Code of Federal Regulations (CFR) Part 192.801 Subpart N provide minimum requirements for\noperator qualifications for individuals performing covered tasks on a pipeline facility. The Atmos\nemployees and contractors associated with the accidents met Atmos’s operator qualifications. (e) An\nindication of natural gas is an observable sign, such as a reading from a detection instrument, that\nnatural gas may be present.\n5\n\n<<<PAGE 17>>>\n\nPipeline Investigation Report\nReport Number PIR-26-01\nthe future.\n10 (This report’s references to leaks refer to belowground leaks unless\notherwise noted. Aboveground leaks can also occur in pipeline systems; however,\nthis report focuses on belowground leaks.)\nMany natural gas distribution pipeline operators use Gas Piping Technology\nCommittee criteria to evaluate leaks, which include elements such as leak location,\ngas concentration (percentage of gas in air), gas migration potential, and soil\nconditions.11 Technicians use these criteria to determine whether to classify leaks as\ngrade 1, grade 2, or grade 3. According to Gas Piping Technology Committee\nstandards, grade 1 leaks are hazardous and include gas leaks that have migrated into\nor under a building. (Gas migration occurs when underground gas escapes and\ntravels through soil, rocks, or wells to the surface or to nearby buildings.) Grade 2\nleaks are nonhazardous (and require scheduled repair based on possible future\nhazard) and include gas leaks that under frozen or adverse-soil conditions would be\nlikely to migrate to the outside wall of a building. Grade 3 leaks are also\nnonhazardous (but do not require scheduled repair) and include gas leaks that are\nunder a street in areas without wall-to-wall paving where it is unlikely the gas could\nmigrate to the outside wall of a building.12\nBased on its classification procedures at the time for grade 2 leaks in\nMississippi, Atmos scheduled the leak to be reevaluated every 6 months and repaired\nwithin 1 year (not to exceed 15 months).\n13 (See section 1.9.1 for more information on\nAtmos’s leak management procedures.) At the time of the leak survey, the city of\nJackson was in a cycle of dry weather, which causes expansive soil to shrink (the\nBristol Boulevard accident home was constructed on expansive soil).\n(See section 1.3 for more information on the weather.)\nOn November 20, 2023, 3 days after Atmos first identified the leak, the\nBristol Boulevard accident homeowner smelled natural gas odorant near the home\n10 During this survey, the technician recorded 100% gas in a bar hole that was about 48 feet\nfrom the building, criteria that, among other factors, resulted in him classifying the leak as grade 2.\n11 Federal regulat","truncated":true,"body_characters":214703}