Photo of the remnants of house where the fatality and two severe injuries occurred.

​Remnants of house where the fatality and two severe injuries occurred​​.

Overpressurization of Natural Gas Distribution System, Explosions, and Fires

Investigation Details

What Happened

​​On September 13, 2018, about 4:00 p.m. local time, a series of structure fires and
explosions occurred after high-pressure natural gas was released into a low-pressure natural gas
distribution system in the northeast region of the Merrimack Valley in the Commonwealth of
Massachusetts. The natural gas distribution system was owned and operated by Columbia Gas of
Massachusetts (CMA), a subsidiary of NiSource, Inc. CMA delivers natural gas to about
325,000 customers in Massachusetts. The fires and explosions damaged 131 structures, including at least 5 homes that were destroyed in the city of Lawrence and the towns of Andover and North Andover. ​Most of the damage occurred from fires ignited by natural gas-fueled
appliances; several of the homes were destroyed by natural gas-fueled explosions. Fire
departments from the three municipalities were dispatched to the fires and explosions. First
responders initiated the Massachusetts fire-mobilization plan and received mutual aid from
neighboring districts in Massachusetts, New Hampshire, and Maine. Emergency management
officials had National Grid United States (NG) (the electric utility) shut down electrical power in
the area, the state police closed local roads, and freight and passenger railroad operations in the
area were suspended. 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


What We Found

​​​We determined that the probable cause of the overpressurization of the natural gas distribution system and the resulting fires and explosions was Columbia Gas of Massachusetts’ weak engineering management that did not adequately plan, review, sequence, and oversee the construction project that led to the abandonment of a cast iron main without first relocating regulator sensing lines to the new polyethylene main. Contributing to the accident was a low-pressure natural gas distribution system designed and operated without adequate overpressure protection.​​

What We Recommended

​We made recommendations to ​the Pipeline and Hazardous Materials Safety Administration, To the States of Alabama, Alaska, Arizona, Arkansas, California, Colorado, ​Connecticut, Florida, Georgia, Idaho, Illinois, Iowa, Kentucky, Louisiana, Maine,​ Maryland, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, New York, North Carolina, Ohio, Pennsylvania, South Carolina, South Dakota, Texas, Utah, Virginia, Wisconsin, and Wyoming, To the Commonwealth of Massachusetts Executive Office of Public Safety and ​Security and To NiSource, Inc.​​​

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