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The natural gas disaster that shook the Merrimack Valley in September 2018 was preceded by mistakes within the utility Columbia Gas in the years before, including shoddy record-keeping that led to the omission of a key safety feature in a construction project, according to a federal investigation that placed the blame for the catastrophe squarely on the utility.

The National Transportation Safety Board issued its final findings Tuesday, concluding that Columbia Gas of Massachusetts had a “weak engineering management” system, where information about safety sensors was missing from construction plans, and company officials had to scramble to locate shut-off valves as more than 130 fires and explosions ripped through three communities on Sept. 13, 2018, killing one person and injuring two dozen.

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The official findings were laid out during an NTSB hearing in Washington, D.C., at which board members and staff were critical of Columbia’s record-keeping, leading up to a tragedy that officials said could have been prevented if better safety systems were in place.

“The project was not done right. It was done wrong. The results . . . were catastrophic,” said NTSB chairman Robert L. Sumwalt

The findings were more detailed than the interim report the agency issued last year in which it pinpointed as the triggering event the failure of a Columbia engineer with limited experience to include a pressure sensor in a gas main replacement project. The failure to locate the sensor led to gas being pushed into the system beyond pressure limits, igniting the fires and explosions across Andover, Lawrence, and North Andover.

The conclusion issued Tuesday went even further, noting the sensor locations were not even included in the records the engineer first consulted in 2016 as he drafted the construction plan. The NTSB noted that a Columbia employee who had reviewed the construction drawings cited the need to relocate the sensor in an October 2016 e-mail, but the omission was never corrected.

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“They knew that these sensing lines had to be relocated. They knew that. But the constructability reviews, the project reviews, the reviews by mangers, engineers, none of this review process addressed the shortcoming,” said Roger D. Evans, NTSB investigator in charge.

The NTSB pointed out that Columbia executives had been made aware of the dangers of over-pressurization in 2015, when its corporate parent, NiSource Inc., sent a notice to its subsidiaries reporting a problem with a sensor at one of its holdings in Kentucky, warning that over-pressurization “may lead to a catastrophic event.”

The NTSB said that Columbia Gas officials in Massachusetts failed to heed that warning.

The NTSB said it has investigated seven similar situations over the past 50 years, including one in 1977 in which a pipe replacement project disrupted a sensor, leading to high pressure in the system.

The board also found that poor record-keeping hampered Columbia Gas’s response to the disaster, adding to the confusion between the company and emergency responders in those first hours. For example, Columbia did not have a readily available map of all of the shut-off valves that needed to be closed immediately. Later in the night, Columbia could not provide a map of the affected area.

“It’s amazing to me that a company that operated this system for more than 100 years could not produce a map, a readily made map, to firefighters to show the extent of the system,” said Robert Hall, director of the NTSB’s Office of Railroad, Pipeline and Hazardous Materials.

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The report also laid out several recommendations, including that the US Pipeline and Hazardous Materials Safety Administration, which oversees the gas industry, set out new requirements for utilities to install fail-safe protections against over-pressurization.

The NTSB also called for a universal requirement that certified professional engineers be required to sign off on significant construction projects on gas systems. Currently, 31 states have exemptions that do no not require a professional engineer; Massachusetts did not require a professional engineer at the time of the disaster but has since adopted the requirement.

In a statement, NiSource said it has already begun working to improve its systems and procedures, for example, installing devices that automatically shut down areas of its network when overly high levels of gas pressure are detected. The company has also implemented a Safety Management System that enhances the company’s emergency preparedness.

“The NTSB’s work is an important step in the effort to enhance pipeline safety,” the statement said. “Our own understanding of the events generally aligns with that of the NTSB. We welcome today’s action by the NTSB because it will help us, our industry partners, the public, and others learn from this tragedy. As we’ve said since that tragic day, we take responsibility for what happened.”

Lawrence Mayor Daniel Rivera, among Columbia’s strongest critics, said the final NTSB report affirmed what he and other municipal officials had been saying all along: that Columbia officials in the hours after the incident were slow to respond and provide information.

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“What the report shows was what we were feeling on the ground . . . they had not command in control,” Rivera said. “We’re now seeing the full picture.”

Rivera said he was equally disturbed by the NTSB disclosure that Columbia had been warned in 2015 about sensors and over-pressure incidents, and did not appear to take preventative measures.

“This whole thing could have been avoided,” Rivera said. “This was absolutely avoidable. But the thing for me, in the end, is that this wasn’t just one thing that went wrong. It was an orchestra of failures.”

The NTSB did note that the communications systems used by emergency responders in the Lawrence area were overwhelmed in the immediate aftermath of the incident; Lawrence fire officials had only one radio channel operating, for instance, and outside agencies that responded with offers of assistance cluttered the airwaves. The NTSB recommended the state revisit its emergency response plans.

Senator Edward Markey, who held a congressional hearing in Lawrence after the disaster and has proposed legislation that would reform the gas industry, praised the NTSB for outlining what went wrong and laying out “concrete steps to keep a similar catastrophe from ever happening again.” He said he has organized a meeting between the NTSB and members of the Greater Lawrence community in October.


Milton J. Valencia can be reached at milton.valencia@globe.com. Follow him on Twitter @miltonvalencia.

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