Incident Overview:

On September 13, 2018, at approximately 4:00 p.m. EDT, a low-pressure natural gas distribution system serving the Merrimack Valley region of Massachusetts, affecting the communities of Lawrence, Andover, and North Andover, was overpressurized during a cast iron main replacement project. The incident resulted in an explosion and multiple structural fires, causing one fatality, 22 injuries, and damage to 131 structures. Additionally, five homes were destroyed. Emergency management officials shut down electric service to the affected towns, the state police closed local roads, and freight and passenger railroad operations in the area were suspended. Columbia Gas of Massachusetts (CMA) shut down the low-pressure natural gas distribution system, affecting 10,894 customers, including some outside the affected area who had their service shut off as a precaution.

Key Findings (Non-Exhaustive) – Refer to Attached NTSB Report for Additional Findings:

• The proximate cause was the over-pressurization of a low-pressure system when the low-pressure system was depressurized without first relocating regulator sensing lines onto the newly installed polyethylene gas main, causing higher-pressure gas to be introduced into the low-pressure system.

• A contributing factor was that the low-pressure mains were designed and operated with a single layer of overpressure protection.

• There were gaps in engineering planning, design, review, documentation, and record-keeping processes, including the constructability review process, which led to the omission of the work required to transfer the existing sensing lines onto the newly installed PE main as part of the replacement project.

• The gas main replacement project was stopped due to unforeseen issues and restarted after a significant delay. This led to a change in the personnel responsible for overseeing the project, a change in contractor personnel working on the project, and field changes needed due to street resurfacing within the original project scope. The management of these changes was an additional contributing factor.

• The need for emergency planning for an event of this scale or that could involve multiple jurisdictions is evident.

Key Lessons Learned (Non-Exhaustive):

• Engineering and Operations Oversight: The planning and review processes for all work to be performed on a natural gas distribution system must be comprehensive and include all components that will or could be impacted by the work to be performed. This is especially critical for projects that may impact pressure regulation stations or equipment. It is also critical that Operations personnel, such as Pressure Regulation and Control, be involved in planning and reviewing gas infrastructure projects that may impact pressure regulation systems and equipment.

• Overpressure Protection (OPP): The sole use of regulators and sensing lines for overpressure protection may not be optimal, and operators should continue to assess this risk on their systems and make improvements as needed or required.

• Management of Change: Long durationprojects, or projects delayed and restarted for unforeseen issues, are susceptible to multiple changes during the project life cycle. These changes must be contemplated and managed through management of change processes.  Examples of such changes include change of operator or contractor personnel during the project, changes to the gas system configuration from other work being performed, as well as changes to the sequencing of project work activities.

• Emergency Planning and Response: Emergency Response Plans should be reviewed considering the nature of large-scale incidents, including pre-planning and coordination with first responders and local officials. The review should also consider how event escalation should trigger the activation of mutual aid.

Key Considerations (Non-Exhaustive):

• Review and update project planning requirements to ensure any potential risks/gaps are addressed. Refer to the NGA Guidelines for Gas System Engineering Design Review.

• Consider performing a detailed risk assessment for each regulator station design that is in service or in planning to identify the need for additional overpressure protection.

• Review pre-planning, pre-mobilization, and pre-construction job site walk-throughs to ensure they are comprehensive and are performed, documented, and communicated to all stakeholders. Refer to NGA Tactical Guide on Mains and Services Construction, as well as the Quick Tips on the same topic.

• Consider temporarily shutting down pressure regulation stations operating within proximity to construction work that may impact station operation, or, at a minimum, have trained and qualified personnel stand by such facilities that cannot be taken out of service.

• Review MOC processes to ensure changes encountered during a project are managed, including personnel changes, and changes to system components and configuration.

• Review emergency planning activities and consider approach to planning/coordination of a large-scale, multi-jurisdictional event. Refer to the NGA Tactical Guide on Emergency Preparedness and Response.

Review NTSB’s Investigation here: https://www.ntsb.gov/investigations/Pages/pld18mr003.aspx