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Human error played key role in Mass. gas explosions, federal report says

Human error likely played a critical role in the explosions and fires on the Columbia Gas of Massachusetts natural gas distribution system that killed one person and injured about two dozen others, according to an Oct. 11 preliminary report from the National Transportation Safety Board.

Prior to the fires, a utility-contracted work crew took an old pipe out of service and installed a new one but left key pressure-sensing equipment active on the old line. The sensors were in communication with nearby regulator equipment that determines how much gas should flow through the system. Because the sensors — which were monitoring the now-abandoned pipeline — detected abnormally low pressure, they prompted the regulator to send increasing amounts of gas through the active system.

"Columbia Gas developed and approved the work package executed on the day of the accident," the NTSB report said. "The work package did not account for the location of the sensing lines or require their relocation to ensure the regulators were sensing actual system pressure."

SNL Image

The one fatality in the series of explosions and fires occurred at this home when its chimney collapsed on the vehicle in the driveway.

Source: National Transportation Safety Board

The excessive pressure caused the fires and blasts in Lawrence, Andover and North Andover, Mass., that killed one person, sent at least 21 people to the hospital and damaged 131 structures, including at least five homes, the NTSB report said.

In that part of the state, Columbia Gas of Massachusetts, formally known as Bay State Gas Co., has a significant amount of older, low-pressure infrastructure. A low-pressure gas system is one in which the gas pressure on the mains and service lines is close to the pressure that is used inside of homes and businesses. On this kind of system, each building does not need its own pressure regulator, so when the pressure spiked on the Columbia Gas system, there were no regulators downstream to step the pressure back down before the gas entered buildings, the NTSB said.

A few minutes before the first fires and explosions, the NiSource Inc. subsidiary's monitoring center in Columbus, Ohio, got two high-pressure alarms from the system in Massachusetts, but the center does not have the ability to close or open valves. The controller did alert Massachusetts personnel of the overpressurization at 4:06 p.m. ET on Sept. 13, but that was only five minutes before a local resident called 911 to report a related incident.

Columbia Gas was able to shut down the regulator by about 4:30 p.m., close critical valves before 7:30 p.m. and begin making the rounds to shut off individual meters by midnight Sept. 14, the NTSB report noted.

SNL Image

The system overpressurization damaged 131 structures. Most of the damage was the result of fires ignited by gas-fueled appliances.

Source: National Transportation Safety Board

NiSource President and CEO Joe Hamrock said in an Oct. 11 statement that in the hours immediately after the incident, the utility suspended the type of replacement and repair work that had resulted in overpressurization, and it enhanced its procedures for dealing with low-pressure systems.

"We saw these as responsible steps to take in the aftermath of the incident and while the facts were being gathered," Hamrock said. "The company is fully cooperating with the NTSB and provided information to assist in its ongoing investigation into relevant facts related to the event, the probable cause, and its development of safety recommendations."

The NTSB said its investigation is still ongoing. It will look into the utility's coordination with emergency responders and the way the utility prepares engineering work plans, among other things.