Probable cause of the two explosions at two separate homes within three days in Jackson was Atmos Energy Corporation’s inadequate leak management program. That allowed for known natural gas leaks from service-line pipes that had partially pulled out of compression couplings due to soil movement.
Contributing to the explosions was Atmos’ inadequate integrity management program. That program did not appropriately assess and address risk in its pipeline system. Also contributing was an ineffective public awareness program. That did not educate the public or emergency response on how to respond to a natural gas leak.
Compression Coupling
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.
NTSB investigators found near the accident homes, natural gas leaked from service-line pipes that had partially pulled out of compression couplings. The gas then 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 movement caused the service-line pipes at both locations to, over time, partially pull out of the compression couplings.
For both incidents, Atmos leak surveys detected belowground leaks weeks before the explosion and classified them as nonhazardous. This nonhazardous classification meant 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. Those leaks were in adverse-soil conditions, which existed in Jackson at the time of the two accidents.
Map and photographs of the accident locations.
Courtesy of Google Earth
As a result, the accident leaks became hazardous before Atmos repaired them.
Several people in the two neighborhoods smelled natural gas odorant and were unaware of pipeline safety guidance. That guidance called for them to evacuate and then immediately report the smell by calling 9-1-1 and the gas company. In the Jackson incidents and in several natural gas accidents, the operator’s public awareness program was ineffective. Instead they need to educate the public on how to safely respond to the smell of natural gas odorant.
Ineffective Communications
Atmos’ ineffective communications regarding the need to report any smell of natural gas odorant inhibited necessary reporting from residents. Additionally, in the two Jackson accidents and in previous Atmos accidents, Atmos missed an opportunity to effectively educate and prepare emergency response officials in its service areas to address natural gas emergencies.
Atmos’ failure to gather relevant information about its service-line records prevented it from effectively assessing the risk to its assets. In addition, Atmos’ distribution integrity management program did not effectively identify and then mitigate the risks to its system.
Also, had anyone placed a natural gas alarm inside the Bristol Boulevard home, it could have alerted occupants natural gas was present. The alarms could prompt residents to evacuate and report the leak. It could also make Atmos aware the leak had likely worsened and required corrective action.
NTSB determines the probable cause of the two explosions at two separate homes in Jackson was Atmos’ inadequate leak management program. That allowed for known natural gas leaks, from service-line pipes that had partially pulled out of compression couplings due to soil movement. That also left the pipes unrepaired for at least eight weeks, resulting in gas leaking and then migrating to the nearby homes and igniting.
Contributing to the explosions was Atmos’ 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.
Aerial photograph of the Bristol Boulevard accident home after the explosion and fire.
Source: Atmos
As a result of this investigation, NTSB made the following safety recommendations:
To the Department of Transportation Office of Inspector General:
Audit the Pipeline and Hazardous Materials Safety Administration’s ongoing joint assessment of Atmos. That should include a review of the company’s approach to the safety management of its pipeline and how it applies lessons learned.
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.
- Evaluate industry’s implementation of the gas distribution pipeline integrity management requirements. It should also develop updated guidance for improving their effectiveness. The evaluation should consider factors that may increase the likelihood of failure such as age, increase the overall risk.
- Identify effective means for natural gas distribution pipeline operators to communicate with people who live or work within the coverage area of a natural gas distribution pipeline system. Implement a plan to help operators drive continuous improvement in public awareness of natural gas safety.
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.
- Update your companywide leak management program procedures. They should require weekly monitoring of nonhazardous (grade 2 or grade 3) belowground leaks identified in locations with adverse-soil conditions.
- Implement a training program to maintain employee and contractor proficiency on the updated procedures.
Develop and implement a program to provide more frequent training to emergency response officials in all the distribution areas. That should include training on how to respond to natural gas-leak calls, and monitor the program for effectiveness. - Require technicians who identify but do not repair a belowground natural gas leak to immediately notify people near the unrepaired leak the hazard potential. They should understand a leak can change over time. They should evacuate and then call 9-1-1 and Atmos every time they smell natural gas odorant.
- Develop and implement a program to proactively identify and collect missing service-line information for all your operating divisions. The program should identify one or more methods for gaining additional system data. It should establish and make public the milestones and timeline for acquiring the unknown system data.
- Transition from a relative-risk model to a probabilistic distribution integrity management risk model.
- Develop and implement a program that makes natural gas alarms available to members of the public who reside in your distribution areas.
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.
Click here for the full report from the NTSB.