Prosecutors have concluded that the metalworkers who inadvertently started a Back Bay fire last year that claimed the lives of two Boston firefighters did not act recklessly and will not be prosecuted criminally.
Investigators found that the nine-alarm fire in March 2014 started when two workers with D&J Ironworks of Malden were welding a wrought-iron railing, sending sparks onto a rotted wooden shed behind a Beacon Street brownstone.
But while the workers acted carelessly, they did not act — or fail to act — with “conscious disregard of a known risk of death or serious injury,” Daniel Conley, the Suffolk County district attorney, said Tuesday.
“We cannot in good faith seek criminal charges for an accident, even one with consequences so tragically devastating,” Conley said in announcing the decision not to bring criminal charges. “Some 60 years of Massachusetts jurisprudence have made clear that negligence, even gross negligence, is in the hands of our civil courts.”
Fanned by gale-force winds, the fire trapped the two firefighters, Edward Walsh Jr. and Michael Kennedy, in the basement after they heard someone might be trapped there. The men were among the first to respond to the fast-moving fire, which destroyed the four-story building.
The yearlong investigation into the fire found that the workers’ conduct fell short of the threshold required for criminal prosecution.
“The standard for criminal prosecution in a case like this is recognizing a grave risk and choosing to run that risk,” Conley said. “The investigation revealed actions that were irresponsible and even careless, but not willful, wanton, and reckless as our courts have defined those terms.”
Conley and his senior staff met last week with the Walsh and Kennedy families and leaders of the Boston Fire Department to inform of them of his decision.
Investigators found that two workers from the Malden metalworking company arrived in the Back Bay around noon on March 26, 2014, to install railings at the rear of 296 Beacon St., the building adjacent to the scene of the fire.
But one railing did not fit, and the workers began to grind and weld it to size. One held a piece of wood to contain the sparks, but at some point either sparks or metal runoff ignited the “highly combustible” shed behind 298 Beacon St.
Around 2:30 p.m., the workers smelled something burning and saw smoke coming from the base of the shed where it met the brick building. The workers tried dousing it with snow, but the fire was already too strong.
Both workers told investigators they shouted warnings to tenants, which was consistent with some witness statements. The men moved their truck away from the shed but did not leave the scene, the investigation found.
The company did not have a required permit for the work. Under the permit, the welders would have had to have outside supervision as a safety measure.
The welding company has been sued in civil court by the owner of the apartment building.
Prosecutors said they considered charging the workmen with a criminal violation of the state fire code, but that would have also required proof of “wanton and reckless conduct.”
The Boston firefighters union Tuesday said the investigation exposed a “lack of enforceable oversight” in the fire codes.
State Fire Marshal Stephen D. Coan said he respected the decision not to bring charges but urged officials to support the creation of a commission to study whether to strengthen regulations for welders or increase penalties for ignoring the rules.
In September, the federal Occupational Safety & Health Administration fined the company $58,000, accusing them of 10 violations of workplace safety standards. The company’s failure to implement “common-sense safeguards” resulted in a needless fire, the agency said.
The workers should have moved the railing to a safer location and used a trained fire watcher at the site, OSHA found.
On Tuesday, a lawyer for the company’s owner, Giuseppe Falcone, said the workers were “relieved and grateful” that authorities “came to the correct conclusion.”
The fire was a “tragic accident,” lawyer Richard Bardi said, adding that the workers’ thoughts and prayers were with the families of the fallen firefighters.
Mayor Martin J. Walsh and Joseph Finn, the city’s fire commissioner, said they supported Conley’s decision.
“This was not a reckless act, this was a careless act,” Finn said. “I know these two gentlemen didn’t come out that morning with the intention of killing two firefighters.”
Walsh and Kennedy “made a difference that day,” he said.
“Lives were saved on Beacon Street by their actions,” he said.
Finn said a report on the fire by the National Institute for Occupational Safety and Health is expected to be issued in July.
Martin Healy, chief legal counsel for the Massachusetts Bar Association, said the standard for criminal prosecution in such cases is “quite a high threshold to meet.”
“It has to be something that rises to the level of shocking the public,” he said.
Healy noted the decision not to bring criminal charges does not close the door on a civil lawsuit and said the company could well be found liable in a wrongful death suit.
“I don’t believe this is the final chapter,” he said.Evan Allen of the Globe staff contributed to this report. Peter Schworm can be reached at email@example.com. Follow him on Twitter @globepete.