# Atmos Energy Corporation Natural Gas-Fueled Home Explosions and Fires

- **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
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- **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.

Event Type: Accident

Event Date: 2024-01-24

Event City: Jackson

Event State Or Region: MS

Event Country: USA

Pipeline Operator: Atmos Energy Mississippi

Pipeline Type: Distribution

Accident Type: Leak/explosion/fire

Completion Status: Completed

Report Number: PIR2601

Report Date: 2026-03-12

Probable 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.

Tier1Name: Emergency response

Tier2Name: Evacuation

Tier1Name: System operating

Tier2Name: Fire/explosion (post-release)

Tier1Name: System operating

Tier2Name: Product leak/release

Finding Tier1Name: Organizational

Finding Tier2Name: Management

Finding Tier3Name: Policy/procedure

Finding Modifier Name: Pipeline operator

Finding Report Text: Organizational - Management - Policy/procedure - Pipeline operator

Finding Tier1Name: Organizational

Finding Tier2Name: Support/oversight/monitoring

Finding Tier3Name: Oversight

Finding Modifier Name: Pipeline operator

Finding Report Text: Organizational - Support/oversight/monitoring - Oversight - Pipeline operator

Finding Tier1Name: Organizational

Finding Tier2Name: Support/oversight/monitoring

Finding Tier3Name: Oversight

Finding Modifier Name: Federal agency

Finding Report Text: Organizational - Support/oversight/monitoring - Oversight - Federal agency

Finding Tier1Name: Organizational

Finding Tier2Name: Support/oversight/monitoring

Finding Tier3Name: Enforcement

Finding Modifier Name: Federal agency

Finding Report Text: Organizational - Support/oversight/monitoring - Enforcement - Federal agency

Finding Tier1Name: Environment/Infrastructure

Finding Tier2Name: Physical environment

Finding Tier3Name: Soil

Finding Modifier Name: Awareness of condition

Finding Report Text: Environment/Infrastructure - Physical environment - Soil - Awareness of condition

Finding Tier1Name: Pipeline

Finding Tier2Name: Pipline systems/equipment

Finding Tier3Name: Fittings

Finding Modifier Name: Failure

Finding Report Text: Pipeline - Pipline systems/equipment - Fittings - Failure

Official NTSB investigation data. NTSB findings determine probable cause and make safety recommendations; they do not adjudicate civil liability or regulatory violations.

What Happened
On 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.)

What We Found
We 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.

What We Recommended
As a result of this investigation, we made the following new safety recommendations. Read the complete list and status of recommendations.

To 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)

To 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)

To Atmos Energy Corporation:
Develop 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)
Update 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)
After 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)
Develop 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)
Require 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)
Develop 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)
Transition from a relative-risk model to a probabilistic distribution integrity management risk model. (P-26-9)
Develop and implement a program that makes natural gas alarms available to members of the public who reside in your distribution areas. (P-26-10)

We reiterated the following safety recommendations

To the Pipeline and Hazardous Material Safety Administration:
Evaluate 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)
Identify 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)
To 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)

PIR-26-01
<<<PAGE 1>>>

March 12, 2026 Pipeline Investigation Report PIR-26-01
Atmos Energy Corporation Natural
Gas-Fueled Home Explosions and Fires
Jackson, Mississippi
January 24, 2024, and January 27, 2024
Abstract: This report discusses the January 2024 natural gas-fueled explosions and
fires at two separate homes in Jackson, Mississippi, which occurred 3 days apart,
collectively resulting in one injury, one fatality, and three destroyed homes. Safety
issues identified in this report include compression coupling leaks, insufficient leak
management program, inadequate distribution integrity management program,
ineffective public awareness program, and absence of natural gas detection alarms in
buildings. As part of this investigation, the National Transportation Safety Board
issued safety recommendations to the Department of Transportation Office of
Inspector General, the Pipeline and Hazardous Materials Safety Administration, and
Atmos Energy Corporation and reiterated recommendations to the Pipeline and
Hazardous Materials Safety Administration and to 50 states, the Commonwealth of
Puerto Rico, and the District of Columbia.

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Pipeline Investigation Report
Report Number PIR-26-01
Contents
Contents ................................................................................................................. i
Figures ..................................................................................................................iv
Tables ....................................................................................................................vi
Acronyms and Abbreviations ...............................................................................vii
Executive Summary ............................................................................................. viii
What Happened............................................................................................................. viii
What We Found ............................................................................................................. viii
What We Recommended ............................................................................................... ix
1 Factual Information ......................................................................................... 1
1.1 The Accidents ........................................................................................................... 1
1.1.1 Bristol Boulevard ............................................................................................. 3
1.1.2 Shalimar Drive .................................................................................................. 9
1.2 Emergency Response ............................................................................................ 13
1.2.1 Bristol Boulevard ........................................................................................... 13
1.2.2 Shalimar Drive ................................................................................................ 14
1.3 Weather ................................................................................................................... 15
1.3.1 Bristol Boulevard ........................................................................................... 15
1.3.2 Shalimar Drive ................................................................................................ 16
1.4 Expansive Soil ......................................................................................................... 16
1.5 Dresser Style 90 Compression Coupling ............................................................ 19
1.6 Examinations and Testing ..................................................................................... 20
1.6.1 On-Scene Examinations and Testing .......................................................... 20
1.6.2 Laboratory Examinations and Testing ........................................................ 27
1.7 Regulations and Advisory Bulletins ..................................................................... 35
1.7.1 Regulations ..................................................................................................... 35
1.7.2 Advisories and Reports ................................................................................. 37
1.8 Atmos Energy Corporation ................................................................................... 38
1.8.1 Company Overview ....................................................................................... 38
1.8.2 Pipeline Safety Management Systems ........................................................ 39
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1.8.3 Safety Performance ....................................................................................... 40
1.9 Procedures and Policies ........................................................................................ 40
1.9.1 Leak Management ......................................................................................... 40
1.9.2 Public Awareness ........................................................................................... 48
1.9.3 Distribution Integrity Management ............................................................. 52
1.10Relevant Atmos Accidents .................................................................................... 56
1.11State and Federal Oversight ................................................................................. 58
1.12Postaccident Actions ............................................................................................. 58
1.12.1 Pipeline and Hazardous Materials Safety Administration ................. 58
1.12.2 Mississippi Public Service Commission .............................................. 59
1.12.3 Atmos Energy Corporation .................................................................. 59
2 Analysis ......................................................................................................... 62
2.1 Introduction ............................................................................................................ 62
2.2 Compression Coupling Leaks .............................................................................. 63
2.3 Insufficient Leak Management Program ............................................................. 68
2.3.1 Leak Repair and Leak Reevaluation ............................................................ 68
2.3.2 Leak Monitoring ............................................................................................. 68
2.4 Ineffective Public Awareness Program ................................................................ 70
2.4.1 Public Awareness Program Effectiveness ................................................... 70
2.4.2 Odor Complaints ........................................................................................... 74
2.5 Inadequate Distribution Integrity Management Program ................................ 75
2.5.1 System Data .................................................................................................... 75
2.5.2 Risk Model ...................................................................................................... 76
2.6 Absence of Natural Gas Detection Alarms in Buildings .................................... 81
3 Conclusions ................................................................................................... 84
3.1 Findings ................................................................................................................... 84
3.2 Probable Cause ...................................................................................................... 85
4 Recommendations ........................................................................................ 86
4.1 New Recommendations ........................................................................................ 86
4.2 Previously Issued Recommendations Reiterated in This Report ...................... 87
Appendixes ......................................................................................................... 89
ii

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Pipeline Investigation Report
Report Number PIR-26-01
Appendix A: Investigation ............................................................................................ 89
Appendix B: Consolidated Recommendation Information ..................................... 90
References........................................................................................................... 94
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Figures
Figure 1. Map and photographs of the accident locations. (Courtesy of Google Earth,
the Pipeline and Hazardous Materials Safety Administration, and the Mississippi
Public Service Commission [clockwise from the top].) ...................................................... 2
Figure 2. The Bristol Boulevard accident home before the explosion. (Courtesy of
Google Maps.) ........................................................................................................................ 4
Figure 3. The Bristol Boulevard accident neighborhood. ................................................. 5
Figure 4. Aerial photograph of the Bristol Boulevard accident home after the
explosion and fire. (Courtesy of Atmos.) ............................................................................. 8
Figure 5. The Shalimar Drive accident home before the explosion. (Courtesy of
Google Maps.) ...................................................................................................................... 10
Figure 6. The Shalimar Drive accident neighborhood. ................................................... 11
Figure 7. The Shalimar Drive accident home (left) and the Shalimar Drive affected
home (right) after the explosion and fires. (Courtesy of the Mississippi Public Service
Commission.) ........................................................................................................................ 12
Figure 8. US expansive soil map overlaid with Atmos’s headquarters (starred) and
regional divisions. (Courtesy of the US Geological Survey and Atmos with NTSB
annotations.) .......................................................................................................................... 17
Figure 9. A Dresser Style 90 compression coupling. ....................................................... 20
Figure 10. Postaccident bar-hole testing and open-air testing conducted at
Bristol Boulevard on January 24, 2024, about 12:42 p.m. .............................................. 22
Figure 11. Postaccident bar-hole testing and open-air testing conducted at
Bristol Boulevard on January 29, 2024, about 9:15 a.m. ................................................ 23
Figure 12. Postaccident bar-hole testing and open-air testing conducted at
Shalimar Drive on January 27, 2024, about 5:30 a.m. ..................................................... 25
Figure 13. Postaccident bar-hole testing and open-air testing conducted at
Shalimar Drive on January 29, 2024, about 9:40 a.m. ..................................................... 26
Figure 14. The Bristol Boulevard natural gas pipeline assembly. .................................. 28
Figure 15. Scratches on the upstream end of the service line at Bristol Boulevard..... 29
Figure 16. Excavation photograph of the copper-water pipeline and the service line
near the Bristol Boulevard accident location. (Courtesy of Atmos.) .............................. 30
Figure 17. The Shalimar Drive natural gas pipeline assembly. ....................................... 32
Figure 18. Scratches on the upstream end of the service line at Shalimar Drive. ........ 33
Figure 19. The Shalimar Drive service-line pipe and gasket. ......................................... 34
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Pipeline Investigation Report
Report Number PIR-26-01
Figure 20. Map of hazardous leaks within a 5-mile radius of Jackson that Atmos
repaired in 2023. (Courtesy of ESRI ArcGIS and Atmos with NTSB annotations.) ....... 41
Figure 21. Map of open leaks within a 5-mile radius of Jackson on January 24, 2024,
including leaks that later met criteria for higher grade leaks. (Courtesy of ESRI ArcGIS
and Atmos with NTSB annotations.) ................................................................................... 43
Figure 22. Map of the Atmos risk model’s high-risk grids in Jackson as of January 24,
2024. (Courtesy of Atmos with NTSB annotations.) ......................................................... 55
Figure 23. Map of hazardous leaks within a 5-mile radius of Jackson that Atmos
repaired in 2023 overlaid with Atmos high-risk grids current on that date. (Courtesy of
ESRI ArcGIS and Atmos with NTSB annotations.) ............................................................. 77
Figure 24. Map of open, nonhazardous leaks within a 5-mile radius of Jackson as of
January 24, 2024, including leaks that later met criteria for higher grade leaks,
overlaid with Atmos high-risk grids current on that date. (Courtesy of ESRI ArcGIS and
Atmos with NTSB annotations.) .......................................................................................... 79
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Pipeline Investigation Report
Report Number PIR-26-01
Tables
Table 1. Timeline of Bristol Boulevard accident events. .................................................... 9
Table 2. Timeline of Shalimar Drive accident events. ...................................................... 12
Table 3. Atmos leak classification procedures. ................................................................. 46
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Pipeline Investigation Report
Report Number PIR-26-01
Acronyms and Abbreviations
Abbreviation Name
ASCE
CFR
GPTC
JFD
MS PSC
MSU
MAFES
NTSB
O&M
PHMSA
psig
PSMS
SME
American Society of Civil Engineers
Code of Federal Regulations
Gas Piping Technology Committee
Jackson Fire Department
Mississippi Public Service Commission
Mississippi State University
Mississippi Agricultural and Forestry Experiment Station
National Transportation Safety Board
operations and maintenance
Pipeline and Hazardous Materials Safety Administration
pounds per square inch, gauge
Pipeline Safety Management Systems
subject matter expert
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Pipeline Investigation Report
Report Number PIR-26-01
Executive Summary
What Happened
On 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.)
What We Found
We found that near the accident homes, natural gas leaked from service-line
pipes that had partially pulled out of compression couplings and migrated through
the ground and into the homes where it fueled the explosions. The leaks near the
accident homes were the result of expansive clay soil movement that caused the
service-line pipes at both locations to, over time, partially pull out of the compression
couplings. For both accidents, Atmos Energy Corporation (Atmos) leak surveys
detected belowground leaks weeks before the explosion and classified them as
nonhazardous. This nonhazardous classification meant that Atmos would not repair
the leaks immediately. Atmos did not have companywide leak management
procedures requiring employees to frequently monitor open, belowground natural
gas leaks located in adverse-soil conditions, which existed in Jackson, Mississippi, at
the time of the two accidents. As a result, the accident leaks became hazardous
before Atmos repaired them.
Several people in the two accident neighborhoods smelled natural gas
odorant and were unaware of pipeline safety guidance to evacuate and then
immediately report the smell by calling 9-1-1 and the gas company. In the accidents
in Jackson, Mississippi, and in several natural gas accidents that the NTSB has
investigated, the operator’s public awareness program was ineffective at educating
the public on how to safely respond to the smell of natural gas odorant. Atmos’s
ineffective communications regarding the need to report any smell of natural gas
odorant inhibited necessary reporting from residents who continued to smell natural
gas odorant in and near their homes. In addition, in the two Jackson accidents and in
previous Atmos accidents in Dallas, Texas, and Avondale, Louisiana, Atmos missed an
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Pipeline Investigation Report
Report Number PIR-26-01
opportunity to effectively educate and prepare emergency response officials in its
service areas to address natural gas emergencies.
Atmos’s failure to gather relevant information about its service-line records
prevented it from effectively assessing the risk to its assets. In addition, Atmos’s
distribution integrity management program did not effectively identify and then
mitigate the risks to its system. Also, 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.
The National Transportation Safety Board determines 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.
What We Recommended
As a result of this investigation, we issued 10 new safety recommendations and
reiterated 3 recommendations. We recommended that the Department of
Transportation Office of Inspector General audit the Pipeline and Hazardous
Materials Safety Administration’s ongoing joint assessment of Atmos Energy
Corporation. We recommended that the Pipeline and Hazardous Materials Safety
Administration issue an advisory bulletin urging operators to adopt probabilistic risk
models. We recommended that Atmos:
• Locate and replace all mechanical couplings and mechanical joints in
expansive soils that are not resistant to pipe pullout.
• Require weekly monitoring of nonhazardous belowground leaks
identified in locations with adverse-soil conditions.
• After updating its leak monitoring procedures to address leaks in
adverse-soil conditions, train its technicians.
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Pipeline Investigation Report
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• Train emergency response officials more frequently and monitor the
effectiveness of the training.
• Require technicians to immediately notify people near an unrepaired
leak that the hazard potential of a leak can change over time, and that
they should evacuate the area and then call 9-1-1 and Atmos every time
they smell natural gas odorant.
• Proactively identify and collect missing service-line information for all its
operating divisions.
• Transition from a relative-risk model to a probabilistic risk model.
• Make natural gas alarms available to members of the public who live in
its distribution areas.
We reiterated two recommendations to the Pipeline and Hazardous Materials
Safety Administration. The first was a 2025 recommendation to identify effective
means for natural gas distribution pipeline operators to communicate with people
within the coverage area of a natural gas distribution pipeline system and help
operators improve public awareness of natural gas safety. The second was a 2021
recommendation to evaluate industry implementation of gas distribution pipeline
integrity management requirements and develop updated guidance for improving
the effectiveness of the requirements. We also reiterated a 2025 recommendation to
the 50 States, Puerto Rico, and the District of Columbia to require natural gas alarms
in businesses, residences, and other buildings where people congregate.
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Pipeline Investigation Report
Report Number PIR-26-01
1 Factual Information
1.1 The Accidents
On January 24, 2024, about 8:14 a.m. local time, a home explosion and fire
occurred at 185 Bristol Boulevard (Bristol Boulevard accident home) in Jackson,
Mississippi, resulting in one fatality, one injury, and a destroyed home.1 Three days
later, on January 27, 2024, about 4:34 a.m., approximately 0.7 miles southeast of the
first explosion, another home explosion and fire occurred at 1146 Shalimar Drive
(Shalimar Drive accident home), and the fire spread to a neighboring home, resulting
in two destroyed homes.2 (See figure 1.) At the time of both accidents, weather
conditions included light to heavy rain, and the temperature was about 60˚F.
1 All times are local unless otherwise noted.
2 (a) The Shalimar Drive accident did not result in any injuries. (b) Visit http://www.ntsb.gov to
find additional information in the public docket for this National Transportation Safety Board (NTSB)
accident investigation (case number PLD24FR003). Use the CAROL Query to search safety
recommendations and investigations.
1

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Pipeline Investigation Report
Report Number PIR-26-01
Figure 1. Map and photographs of the accident locations. (Courtesy of Google Earth, the
Pipeline and Hazardous Materials Safety Administration, and the Mississippi Public Service
Commission [clockwise from the top].)
Atmos Energy Corporation (Atmos) owned and operated natural gas pipeline
assets near the Bristol Boulevard accident home and the Shalimar Drive accident
home.
3 Atmos distributed natural gas to both homes with 2-inch diameter
coated-steel gas mains that ran in front of the homes.4 Service lines to individual
homes were connected with 3⁄4-inch steel service tees that were welded on the main
3 (a) See section 1.8 for more information on Atmos. (b) This report uses the term assets to refer
to the specific elements of a pipeline distribution system.
4 (a) A gas main (or main line), which is typically belowground, is a natural gas distribution
pipeline that serves as a common source of supply for more than one service line. (b) The main near
the Bristol Boulevard accident home was installed in 1967; the main near the Shalimar Drive accident
home was installed in 1962.
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Pipeline Investigation Report
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and joined to a 3⁄4-inch steel service line.5 Dresser Style 90 seal-only compression
couplings made the mechanical joints that connected the service lines to the service
tees. (This report’s references to Dresser Style 90 compression couplings refer to the
seal-only design unless otherwise noted. The seal-only design is not configured to
resist pipe pullout, meaning it is not designed to hold the pipe in place. Other
versions of the Dresser Style 90 compression coupling include a clamping design that
resists pipe pullout; however, the seal-only design does not.) (See section 1.5 for
more information on Dresser Style 90 compression couplings.) Around the time of
the two accidents, the gas mains near both homes were operating below the
maximum allowable operating pressure of 40 pounds per square inch, gauge (psig).
6
1.1.1 Bristol Boulevard
The Bristol Boulevard accident home, built in 1972, was a single-story,
single-family, wood-framed structure with masonry construction on a concrete
foundation. (See figure 2.) The home was constructed on soil composed of Yazoo
clay, an expansive clay prone to movement (shrinking and swelling) during cycles of
dry and wet weather.
7 (See section 1.4 for more information on expansive soil.)
5 (a) A service line, which is typically belowground except when it is near a gas meter, is a
pipeline that transports natural gas (or another commodity) to a customer. (b) The NTSB could not
confirm the service-line installation dates (Atmos reported that it did not have the installation records
for the service lines at the two accident homes.); however, the NTSB determined that the accident
compression couplings contained components manufactured in or before 1963. (c) Compression
couplings are a type of mechanical fitting (or mechanical coupling) used to join and pressure seal two
pipes together without requiring soldering, welding, or threading. (d) A service tee, which is typically
belowground, creates a branch connection that enables a service line to connect to a main.
6 (a) At the time of the Bristol Boulevard accident, the main near the Bristol Boulevard accident
home was estimated to be operating about 36.5 psig. At the time of the Shalimar Drive accident, the
main near the Shalimar Drive accident home was estimated to be operating about 36.6 psig. The NTSB
also reviewed the operating pressure histories for both accident locations, and they were below the
maximum allowable operating pressure. (b) Natural gas distribution operators typically conduct
pipeline operations slightly below the maximum allowable operating pressure to allow for potential
pressure fluctuations.
7 (a) Soil is composed of sand, silt, and clay. (b) Expansive soil is soil that undergoes significant
volume changes—shrinking when dry and swelling when wet—because of its high clay content.
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Pipeline Investigation Report
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Figure 2. The Bristol Boulevard accident home before the explosion. (Courtesy of
Google Maps.)
While Atmos provided natural gas service to the Bristol Boulevard accident
home, it did not provide gas service to all the homes in the neighborhood, including
the home at 175 Bristol Boulevard (Bristol Boulevard affected home), at which,
postaccident, Atmos bar-hole testing detected explosive levels of natural gas.8 Figure
3 shows the accident neighborhood, indicating the homes that had natural gas
service and those that did not. It also shows the accident leak location, which will be
discussed in section 1.6.1.1.2.
8 Bar-hole testing describes a gas measurement technique in which a technician makes a small
diameter hole in the ground with a steel bar, inserts a probe into the hole, and obtains a gas
measurement. Technicians review bar-hole readings to determine the extent of natural gas in the
ground in the tested area. (See section 1.6 for more information on this and other accident-related
examinations and testing.)
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Pipeline Investigation Report
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Figure 3. The Bristol Boulevard accident neighborhood.
About 9 weeks before the accident on Bristol Boulevard, on
November 17, 2023, after a routine, periodic mobile leak survey detected an
indication of natural gas, an Atmos contractor, a survey technician, investigated the
indication by conducting a walking leak survey near the Bristol Boulevard accident
home.
9 (Atmos conducted walking leak surveys in response to mobile leak surveys
that detected indications of natural gas.) The technician located a leak and classified
the leak as grade 2, meaning he determined the leak was nonhazardous at that time
but noted that it required a scheduled repair because it could become hazardous in
9 (a) Atmos’s procedures required it to conduct mobile leak surveys every 5 years. (b) In a
mobile leak survey, the pipeline operator deploys a vehicle (such as a truck or an aircraft) with
mobile-data collection equipment to detect methane concentrations (the primary component of
natural gas is methane). (c) In a walking leak survey, a technician walks near or over gas mains and
service lines and up to each meter set (the gas meter and associated components) in the survey area
while carrying a handheld leak-detection instrument. (d) Federal regulations in
Title 49 Code of Federal Regulations (CFR) Part 192.801 Subpart N provide minimum requirements for
operator qualifications for individuals performing covered tasks on a pipeline facility. The Atmos
employees and contractors associated with the accidents met Atmos’s operator qualifications. (e) An
indication of natural gas is an observable sign, such as a reading from a detection instrument, that
natural gas may be present.
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Pipeline Investigation Report
Report Number PIR-26-01
the future.
10 (This report’s references to leaks refer to belowground leaks unless
otherwise noted. Aboveground leaks can also occur in pipeline systems; however,
this report focuses on belowground leaks.)
Many natural gas distribution pipeline operators use Gas Piping Technology
Committee criteria to evaluate leaks, which include elements such as leak location,
gas concentration (percentage of gas in air), gas migration potential, and soil
conditions.11 Technicians use these criteria to determine whether to classify leaks as
grade 1, grade 2, or grade 3. According to Gas Piping Technology Committee
standards, grade 1 leaks are hazardous and include gas leaks that have migrated into
or under a building. (Gas migration occurs when underground gas escapes and
travels through soil, rocks, or wells to the surface or to nearby buildings.) Grade 2
leaks are nonhazardous (and require scheduled repair based on possible future
hazard) and include gas leaks that under frozen or adverse-soil conditions would be
likely to migrate to the outside wall of a building. Grade 3 leaks are also
nonhazardous (but do not require scheduled repair) and include gas leaks that are
under a street in areas without wall-to-wall paving where it is unlikely the gas could
migrate to the outside wall of a building.12
Based on its classification procedures at the time for grade 2 leaks in
Mississippi, Atmos scheduled the leak to be reevaluated every 6 months and repaired
within 1 year (not to exceed 15 months).
13 (See section 1.9.1 for more information on
Atmos’s leak management procedures.) At the time of the leak survey, the city of
Jackson was in a cycle of dry weather, which causes expansive soil to shrink (the
Bristol Boulevard accident home was constructed on expansive soil).
(See section 1.3 for more information on the weather.)
On November 20, 2023, 3 days after Atmos first identified the leak, the
Bristol Boulevard accident homeowner smelled natural gas odorant near the home
10 During this survey, the technician recorded 100% gas in a bar hole that was about 48 feet
from the building, criteria that, among other factors, resulted in him classifying the leak as grade 2.
11 Federal regulat
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