BOSTON (CBS) - Investigators say the cause of last week's nine-alarm Beacon Street brownstone fire that killed two Boston firefighters was due to welders working at the rear of the building next door.
Boston Fire Lt. Ed Walsh, 43, and firefighter Michael Kennedy, 33, died when they became trapped in the burning basement of 298 Beacon Street on March 26.
Acting Boston Fire Commissioner John Hasson told reporters at a news conference Friday that welders were working on an iron hand railing behind 296 Beacon Street when the sparks "extended to a wooden structure in the rear" and eventually started the fire at 298 Beacon.
"What happened is probably the slag or the sparks from the welding operation got in under the clapboards or the shingles. It festered there for awhile. The fire ignited. It's an older wooden building. It's probably dried out. The fire got rolling. It was fed by the wind off the Charles (River) and ultimately consumed the whole building," Hasson said.
He later explained in detail how the fire spread.
"The fire got into the structure behind the building, probably got up between the studs into the bay and then it extended vertically and then when the wind coming off the Charles found the opening, the door was left open, and it just extended the fire from the basement up through, ultimately through the roof."
Authorities would not identify the welders or say how many were involved.
Hasson also revealed that there was no fire detail at the scene during the welding and that there is no record of anyone requesting a permit for that job. In most cases, a fire detail is required for welding work, but not in all instances.
"What happens is they apply for a permit. The chief goes out and investigates. The chief will determine what the potential hazards are and then decided whether or not a detail is required," Hasson said.
Hasson told reporters sprinklers "would have been a benefit" but they were not required for that specific building.
Boston Police Commissioner William Evans called the firefighters' deaths "unintentional" at this point in the investigation. Any charges will be determined by the Suffolk County District Attorney's Office.
Edmond Zabin, chief of District Attorney Dan Conley's homicide unit, said they do not believe the fire was intentionally set.
The owners of 296 Beacon Street, Oliver Realty Limited Partnership, released a statement Friday afternoon saying they are "deeply saddened" by the tragic fire.
"Our hearts go out to the families of the firefighters who gave their lives to save others and protect property.
"The company recently contracted with a third party to install safety railings at 296 Beacon Street. It was the company's understanding that these railings would be prefabricated offsite.
"We have cooperated fully with the investigators, providing them with all relevant information, and will continue to do so. The company also expects to launch its own review. "
Watch: Boston Police, Boston Fire Briefing
A fund has been set up to help the firefighters' families.
Donations may be made at the Boston Firefighter's Credit Union website, www.bosfirecu.com, or by mailing checks to the fund care of the Boston Firefighter's Credit Union, 60 Hallet St., Boston MA 02124.
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