Columbia Gas of Massachusetts was not prepared for a disaster on the scale of the explosions and fires that swept through three communities Sept. 13, the state's U.S. senators alleged in an Oct. 4 letter.

"[T]he company underestimated the possibility of an extremely serious incident, did not adequately build redundancies into its operations or put in place key safety measures to prevent it, and was utterly unprepared to respond to it," Democratic Sens. Edward Markey and Elizabeth Warren wrote to the utility and its parent, NiSource Inc.

"Taken together, these failures created conditions that made this disaster a near certainty, yet Columbia Gas does not appear even to have contemplated that an incident of this magnitude could occur," the lawmakers said, noting that they had reviewed multiple procedure documents that the utility provided.

The letter highlighted the risk evaluation part of Columbia Gas of Massachusetts' integrity management plan. In calculating risk, the program assigns a "zero" value to events that have not happened, which minimizes the plan's ability to account for something as rare as a large-scale overpressurization on the system, the letter said. The Columbia Gas plan noted that a "zero" value does not mean there is zero risk associated with the event, but the senators argued that not considering the possibility makes such an event unlikely to be planned for, the letter added.

The lawmakers also questioned whether Columbia Gas' emergency preparedness and incident prevention plans were detailed enough when it comes to addressing human error and whether the emergency shutdown protocols adequately accounted for how to handle a significant system overpressurization. Nearly 86,700 Columbia Gas of Massachusetts customers are still served by low-pressure infrastructure, the letter noted.

The utility, which is formally known as Bay State Gas Co., on Sept. 18 updated its requirements for pipe connections on low-pressure parts of the system — the type of connection work that appeared to have been taking place shortly before the explosions and fires in Lawrence, Andover and North Andover, Mass. The updated guidelines specify that workers should identify the equipment that sends gas directly into the low-pressure system and require monitoring by qualified personnel.

"The omission of these sorts of safety measures from Columbia Gas' operating procedures prior to this disaster is alarming and unacceptable," the letter said. "It raises serious questions as to why these policies were not previously in place for Columbia Gas' systems and whether that failure was the result of negligence, cost considerations or incompetence."

The senators noted that Columbia Gas of Massachusetts had not completed a pipeline safety management system — a recommended practice issued in 2015 by the American Petroleum Institute and embraced by a number of safety experts and regulators. Safety management systems involve a cyclical, holistic approach to understanding and mitigating risk, and while the recommended practice remains voluntary, regulators have sometimes pushed companies to adopt the practice. After the Indiana Utility Regulatory Commission found that fellow NiSource subsidiary Northern Indiana Public Service Co. had violated safety rules by failing to keep accurate records of its underground pipeline facilities, the commission required the utility to adopt a pipeline safety management system and imposed a $900,000 fine.

The senators' letter went on to criticize the company's public communications strategy in the event of an emergency, pointing out that the emergency response plan does not include a timeline for communicating with the public immediately after a disaster. Quickly getting the word out to the public about an ongoing disaster is a critical component of responding to an emergency, the senators argued. One person died, two dozen more were injured and more than 60 locations sustained damage as a result of the Sept. 13 explosions and fires.

"In an emergency of this magnitude, communicating early and often with the public is essential, yet Columbia Gas does not appear to have made any public statements about this disaster for four hours after the explosions began," the letter said.

Markey and Warren requested that the utility and its parent company explain their thought process on a number of these issues and describe what is being done to rectify any deficiencies.

NiSource did not immediately respond to a request for comment on the senators' letter.