A proliferation of lightweight engineered wood in flooring and ceiling structures in residential developments in the Boston area poses more risks and challenges for fire departments, according to fire experts and fire officials.
Two large apartment buildings that have burned in the last month — one in Dorchester in June and the other in Waltham on Sunday — used the material in their structures.
In a fire, lightweight engineered wood burns and collapses much more quickly than traditional dimensional lumber, such as two-by-eight boards.
Engineered support beams are comprised of several layers of plywood-like material pressed into thick boards. And support joints in floors and ceilings are shaped like an I-beam, and are engineered out of two pieces of dimensional lumber with a piece of plywood between them.
Contractors like them because they are lightweight, strong, and sustainable. Experts and contractors who spoke to NBC Boston said the material is safe as long as fire prevention systems, like sprinklers and fire-resistant drywall, are in place.
The greatest risk of fire and structural failure is during construction before the drywall is installed or when the sprinkler system is not operational.
“You have basically a vertical lumber yard with the amount of wood that’s exposed,” said Leonard A. Albanese Jr., Chelsea Fire Chief. “The walls are not yet buttoned up, so you have a heavy fuel load with a great amount of oxygen that can get into the building and it’s ripe for rapid fire spread with those conditions.”
Chelsea saw a burst of construction around Route 1 that included two hotels, a condominium building and a new regional headquarters for the FBI. Many of those buildings are four to six floors high, and contain the engineered lumber.
A 2009 change in the International Building Code allows for builders to use wood, rather than steel and concrete, as the structure in larger and higher multifamily developments. To keep costs down and to allow bigger rooms and higher ceilings, among other reasons, many turn to the lightweight engineered wood to support floors and roofs.
A fire on June 28 destroyed the top floor of an apartment building on Dorchester Avenue in Ashmont. The cause is under investigation, according to the Boston Fire Department, and the sprinkler system was offline.
No one was injured in the fire, and no one had yet moved into the building.
Boston city officials said the building was scheduled for a final inspection, which would have included a sprinkler test, the following day.
In Waltham on Sunday, a five-building residential complex under construction was destroyed by a fast moving fire.
Two firefighters were injured, one with a burned arm, according to Waltham Fire Chief Paul J. Ciccone.
Waltham City Councilor Robert G. Logan, who represents the district where the fire happened, said the state should revisit whether lightweight wood, or lumber in general, should be used in large residential structures.
“At the very least the state needs to go back and look and see if that was really a wise decision to change the building codes the way they did,” he said. “There’s going to be a disaster.”
According to a 2009 Underwriters Laboratories fire study that simulated the weight of two firefighters on a floor supported by engineered wood I-beams and by traditional two-by-six inch dimensional boards, the engineered wood withstood the test fire for six minutes, a third of the time of the traditional dimensional lumber.
“There’s a significant issue that once you start burning the structure, you could have the connections become weakened, you could have what we call a point failure, so that as a firefighter is walking on the floor above, if they walk to a point that’s been weakened due to the fire burning the floor joist, they have the potential to fall through,” said Brian Meacham, an associate professor of Fire Protection Engineering at Worcester Polytechnic Institute.
Meacham conducted his own fire tests with the material in WPI’s fire lab, and he said their results confirmed the UL study’s results.
Fire prevention systems like sprinklers and fire-resistant drywall significantly increases the time until failure by keeping the fire away from the vulnerable pressboard. But if the sprinklers are not on, or there are no sprinklers and the drywall fails, the engineered lumber will burn and collapse in a third of the time of the traditional dimensional lumber, according to the UL studies and Meacham’s tests.
The fire burns quickly through the middle of the “I,” which is comprised of small chips of wood glued and pressed together into a board. Destruction of that support can lead to the entire beam to fail.
“There’s a significant issue that once you start burning the structure, you could have the connections become weakened, you could have what we call a point failure so that as a firefighter is walking on the floor above, if they walk to a point that’s been weakened due to the fire burning the floor joist, they have the potential to fall through,” Meacham said.
A few states and communities require stickers on buildings that use the lightweight engineered lumber to warn firefighters. Acushnet is one, and possibly the only community in Massachusetts to require the stickers. Several states, including Vermont and New York, require them statewide.
Acushnet Fire Chief Kevin Gallagher pushed for the local requirement years ago, said James Marot, the town’s building inspector.
“He wanted to make sure his firefighters and anyone who entered the building knew right away that this building is lightweight construction,” Marot said.
Scott Colwell is a third-generation builder who has been using the lightweight engineered lumber for years. He said the material is safe and doesn't burn any faster than dimensional lumber that is more than a couple years old.
“What people don’t realize is the lightweight is a typical stick lumber, as we call it. After a couple of years, (traditional lumber is) dry as kindling,” he said.
He builds high-end single family homes, and likes the engineered lumber because it doesn’t shrink, doesn’t warp, and allows him to build larger rooms and higher ceilings. His homes are outfitted with fire-resistant drywall and hard-wired smoke and carbon monoxide detectors.
“If you get to the point where the floors are burning, those people are gone,” he said. “And no fire chief is going to send his firefighters in in those conditions.”
Another recent building code change requires any engineered lumber that will remain exposed be coated or treated with a fire retardant.
The American Wood Council said in a statement that fire is a risk in buildings and construction sites no matter what building material is used.
“All building components, such as walls, floors and roofs are designed and rigorously tested to ensure structural fire performance provides enough time for occupants to exit the building and allow emergency responders to perform their duties,” the group said in its statement. “These are further augmented by the use of both active (sprinklers) and passive (fire-rated materials) fire protection measures in completed buildings.”
Fire officials agree that those measures improve safety. But in an advanced fire, lightweight lumber is a hazard they have to consider when attacking a fire.
Just knowing it is there is half of the battle.
“Lightweight trussing systems fail under fire conditions,” Albanese said. “Without fire conditions, they’re great, but under fire conditions they fail early. So there’s a collapse danger which is an added risk for firefighters.”