Echoing the concerns of local lawmakers and keying into a former employee's criticisms, Massachusetts' U.S. senators questioned whether Columbia Gas of Massachusetts has adequate staffing to ensure that it is operating safely.

Democratic Sens. Edward Markey and Elizabeth Warren asked the utility Dec. 16 to explain its staffing choices in the years and months leading up to a deadly series of explosions and fires in September, citing complaints made by a former manager that the utility had cut staffing at its meters and regulations department.

The former meters and regulations manager said publicly that before leaving the company in mid-2018, he had informed his superiors that he was concerned that staffing cuts in his department could affect safety, the senators' letter said.

"Columbia Gas prioritized savings over safety and ignored clear concerns from experienced employees, and the people of Lawrence, Andover, and North Andover paid a devastating price as a result," Warren and Markey said in a Dec. 16 statement. "We are extremely concerned that Columbia Gas failed to heed warnings that Columbia Gas' decisions to cut critical safety staff could lead to disaster."

The utility did not immediately respond to a request for comment on the senators' remarks.

The senators asked Columbia Gas and parent company NiSource Inc. to explain the utility's change in policy in recent years that eliminated the requirement that a particular kind of technician on site at construction projects to monitor gas distribution pipeline pressures.

The lawmakers also asked why the utility, formally known as Bay State Gas Co., had reduced staffing at its meters and regulations department. This segment of the company housed information that could have prevented the September explosions but was not consulted in the course of developing the work plan for construction that immediately preceded the deadly explosions and fires.

State Sen. Michael Barrett, a Democrat, during a Dec. 11 hearing highlighted NiSource's financial performance in recent years but noted an increased reliance on contractor, rather than in-house, labor, especially as the utility has pursued fast-paced replacement of its aging infrastructure.

"For the best of reasons, we've got an accelerated infrastructure build-out statewide right in the teeth of a full-employment economy. ... There must be an expense involved," Barrett said at the hearing, questioning how the company had handled rising labor costs and whether the utility's choices had affected safety.

The Sept. 13 overpressurization on Columbia Gas' system resulted in a series of fires and blasts in Lawrence, Andover and North Andover, Mass., killing one person, sending at least 21 people to the hospital and damaging 131 structures.

Before the overpressurization, a utility-contracted work crew, which included a Columbia Gas inspector, executed one of the company's own designed and approved pipe replacement projects. The crew installed a plastic distribution main and abandoned the cast iron main as planned, but the abandoned line still had sensors that were allowed to remain live. The abandoned line had no gas flowing through it, so these sensors detected abnormally low pressure, causing valves to send excessive gas through the newly installed pipe.

The Columbia Gas plans for the pipe upgrade project did not consider regulator-sensing lines that were connected to the distribution pipes that were slated for abandonment, even though the plans went through the utility's constructability review. The meters and regulations department houses information related to regulator-sensing lines.