She said replacement workers and supervisors were slowly allowing pressure back into the pipes Tuesday and testing the system before turning gas back on to the homes. Some homes would have gas restored Wednesday, she said, and all would be back on line by Thursday. State regulators imposed a moratorium on almost all National Grid work after the pressure spike.

Marcy Reed, the president of National Grid in Massachusetts, declined to detail how the supervisor let too much pressure into the gas line, but said he was an employee with decades of experience.

WOBURN — National Grid on Tuesday defended the use of replacement workers, a day after a supervisor replacing a locked-out union worker injected excess pressure into a gas line, forcing the company to shut off gas to 300 homes here and raising fears of explosions like those that rocked the Merrimack Valley less than a month ago.

“As we’ve said already, this was mostly, we will find out, a point of human error,” Reed said at a news conference. “Mistakes do happen. This could happen regardless of the workforce we have on the ground.”


But the gas workers union said the overpressurization and emergency shutdown proved the point they have been making for weeks: that the lockout of 1,250 National Grid workers poses a serious threat to public safety.

The union workers were locked out in late June after refusing a new contract offer that included higher health care costs and a 401(k)-style retirement package for new hires, instead of the traditional pension plan current employees have. Since then, the company has relied on replacement workers and supervisors to perform routine gas work. One of those supervisors was performing routine maintenance near Wyman and Hart streets on Monday, when he accidentally introduced excess pressure into the system, National Grid said.


“The people who are replacing us, they’re not people who do the job every day,” said John Buonopane, president of the United Steelworkers Local 12012, which represents about a third of the locked-out gas workers. “I honestly believe that if we were working, this would not have occurred.”

Joe Kirylo, president of the Boston Gas Workers Union, echoed the argument. “We are the first line of defense and the last line of defense,” he said. “It is the union that brings the safety attention forward.”

Reed rejected the unions’ claims of a public safety risk. She said the company immediately realized the mistake, reduced the pressure within minutes, and shut off the gas “as a precaution.” No one was evacuated, and officials said the homes were safe.

“I stand by the qualifications and the expertise our workers have,” Reed said. “The most important thing here today is that we’re addressing it safely, the situation is under control, and no one is in harm’s way right now.”

The Woburn incident occurred less than one month after gas fires and explosions ripped through Lawrence, Andover, and North Andover, killing one person and injuring more than 20. Investigators suspect the pressure levels in the pipeline network operated by Columbia Gas of Massachusetts were too high, and the utility is replacing some 45 miles of older gas mains before it restores service to the affected area.

The Lawrence-area disaster has heightened concerns about gas safety, prompting the Massachusetts Department of Public Utilities to hire an independent evaluator to conduct a statewide examination of the safety of the natural gas distribution system.


State oversight of utilities has also sharpened considerably. In late September, the DPU said it was investigating possible pipeline safety violations and related issues by National Grid for work the company has performed during the union lockout. The agency also ordered the company to provide information about staffing, costs, and services it has provided before and during the lockout.

Then a day later, the DPU used unusually harsh language to reject National Grid’s request for a rate increase, saying the utility’s “persistent disregard for federal and state pipeline safety regulations, as evidenced by these numerous enforcement actions, shows a cavalier disregard for Department requirements and a failure to abide by pipeline safety laws and regulations to the detriment of the Companies’ ratepayers.”

In one of those enforcement actions, National Grid was fined $1.25 million in 2015 for 20 pipeline violations on Cape Cod, including not having proper overpressure protections in place on parts of the system. Separately, the company in 2016 agreed to a plan with the DPU to correct problems after failing to comply with a number of consent orders for previous violations.

After Monday’s incident in Woburn, the DPU imposed the moratorium on National Grid work — with the exception of emergency and compliance actions — and required the company to have an inspector on hand for any work that could lead to abnormally high levels of pressure.


National Grid must also give regulators information about the staffing, costs, and services it has provided during the lockout, compared to the same period in previous years.

Reed said the company will also reimburse residents for take-out meals and other expenses associated with the shut-off. “I’m really sorry that we put you through this inconvenience,” she said.

Images of the Merrimack Valley disaster unsettled the Woburn residents who had their gas shut off.

“You feel a little invincible, but I know that with everything that has happened a couple towns over, it could be a potentially serious situation,” said Patty McIntyre, 25, who learned her gas had been shut off Monday morning after she returned from walking her dog. She said she and her boyfriend were planning to cook on their outdoor grill and use a propane camp stove to make coffee.

“We’re literally breaking our camping gear out of the basement,” she said, adding that it was frustrating not to be able to take a hot shower.

Josh Johnstone, 17, who lost gas service at his home, said he ate cold cuts for dinner Monday, had toast for breakfast Tuesday, and showered at his grandfather’s house down the street. He said the situation was scary after the devastation in the Merrimack Valley. “God forbid something happened,” he said, adding he was frustrated with National Grid for locking out workers. “I think it’s terrible what they’re doing to them.”

Near Johnstone’s house on Wyman Street, several dozen locked-out workers held signs, yelling “scabs” at replacement workers, as police kept watch.


Mayor Scott D. Galvin said he was happy with National Grid’s response to the problem and hoped the union and utility would settle their differences.

“We can only say those union workers are skilled; they were certainly trained to do the type of work that we want to see in our city,” he said. “We encourage National Grid and the unions to get back to the table and get it done for the safety of everybody.”

State Representative James J. Dwyer, a Woburn Democrat, said, “We need our locked-out workers back on the job.”

Governor Charlie Baker also hopes for an end to the dispute, said his spokeswoman, Lizzy Guyton, and “has repeatedly called for both sides to reach a compromise and end the lockout.”

Michael Levenson

can be reached at mlevenson@globe.com. Follow him on Twitter @mlevenson. John R. Ellement

can be reached at ellement@globe.com. Follow him on Twitter @JREbosglobe.