Metro

Improperly installed exhaust pipe ignited massive Dorchester fire, commissioner says

A poorly installed exhaust pipe is to blame for the six-alarm fire that tore through the Treadmark building in Dorchester last month, fire officials said Wednesday.

And the error was compounded when construction workers testing a generator waited about 90 minutes to call 911 after they first smelled smoke and saw haze inside the six-story building, said Boston Fire Commissioner Joseph Finn, who released the Fire Department’s report on the fire Wednesday.

The blaze badly damaged the $45 million building, an 83-unit mix of affordable apartments and market-rate condominiums being developed by Boston-based Trinity Financial that was set to open in mid-July. It broke out on the afternoon of June 28 as workers were testing the building’s emergency systems ahead of safety inspections planned for the following day.

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They were testing an emergency generator in the basement, Finn said, and using a cast-iron exhaust pipe, installed the day before, to vent fumes from the generator up through the six-story building and out from the roof. Architectural drawings called for a 12-inch space around the exhaust pipe, Finn said. It was put in place with just 3 inches of clearance. As the pipe heated up, the wood caught fire.

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“It was improperly installed,” Finn said of the piping. “The heat source was too close to combustibles. . . . That was the cause of the fire.”

A Trinity spokeswoman said Wednesday that the fire is “still under investigation by many parties” and declined to comment until those reviews are complete. Cranshaw Construction of Newton, which oversaw construction on the project, also declined to comment until all investigations are finished.

Later Wednesday, Inspectional Services forwarded the Globe a safety violation notice the agency had issued to Trinity after the fire.

The blaze is one of a rash of construction fires nationwide in a type of mid-rise, wood-frame apartment building that has become popular in Greater Boston and across the country in recent years. A similar-style apartment complex under construction in Waltham burned down early Sunday, heightening local calls for stricter fire safety regulations. The cause of that fire was still under investigation Wednesday and the state fire marshal appealed to the public for help to see if anyone has photos or videos of the fire in its early stage.

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Building with wood rather than steel or concrete is less expensive and faster, and building code changes in recent years have allowed for taller wood-frame buildings above a concrete ground floor, making the technique attractive to developers hoping to build more units on expensive land.

And fire experts agree that the buildings are safe once sheetrock, sprinklers, and other safety systems are built in. But once it starts, a fire in an unfinished building can move fast. In the case of Treadmark, sprinklers were installed but not yet activated, Finn said, because it was not yet occupied.

“We would have had a very different outcome” had the sprinklers been on, Finn said, though he noted they are not a cure-all for fire risks, which, he noted, are far higher during construction in this sort of wood-frame building.

He repeatedly pointed to the work crew’s 90-minute delay in alerting firefighters to the blaze. “It’s a grave concern, to be honest with you,” Finn said.

He said city officials must “educate the construction industry in how quickly we need the [911 call] to take place.”

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The string of mishaps was concerning to Jill Grozalsky, a Brighton resident who had purchased one of the condos in August. “To be honest, it’s upsetting to hear the cause of the fire, because it sounds like it could’ve easily been prevented and also that there were mistakes made throughout the day,” Grozalsky wrote in an e-mail Wednesday.

Other would-be tenants said they still plan to move into the Treadmark, whenever it opens. Specialty grocer American Provisions has a lease to put a store in the building’s ground floor. Those plans are still on, said co-owner Andy Fadous.

Trinity has said it plans to salvage as much of the building as possible and has vowed to rebuild it. The city’s Inspectional Services Department is still determining how much of the structure can be kept.

The ISD’s director, William “Buddy” Christopher, said at Wednesday’s news conference that his office is working with fire officials on recommendations to tighten safety protocols and prevent similar fires. But they do not believe problems with wood-frame construction are widespread, or that such projects should stop.

“We do not think this is a systemic problem across the city,” he said.

Close-up view of the damaged window at the Treadmark Building.
David L Ryan/Globe Staff
A damaged window at the Treadmark building.

The Treadmark Building on Wednesday.
David L Ryan/Globe Staff
The Treadmark building on Wednesday.

Andersen can be reached at travis.andersen@globe.com. Logan can be reached at tim.logan@globe.com.