The firefighter ducked into the bedroom, knelt to the wooden floor and lit a fire under a stack of white lounge chairs. Within seconds, huge plumes of ashy smoke and soot lifted, followed closely by a rush of orange flames that leapt through a plywood window.

Heat burst through the room — along with the acrid smell of burning plastic and smoke.

“You’ve got to feel it. You’ve got to smell it,” said Bureau of Alcohol, Tobacco, Firearms and Explosives Special Agent Eric Peña. “You don’t get that from the observation deck.”

The blaze was the first of four set Friday afternoon at the ATF’s Fire Research Laboratory in Beltsville, where about 30 agents from around the country spent last week re-certifying as arson investigators.

The fires concluded an exercise where the investigators tested what they learned during a weeklong session that covered the nature of fire, how it spreads and the science behind it.

The agency holds such classes at venues around the country each year, and this year agents came to the Washington area, home toone of the world’s largest forensics laboratories. The facility houses labs that can dissect ballistic evidence, explosives and, of course, fire and arson investigation.

The complex consists of warehouse spaces, mini-museum and high-tech labs that evoke high school chemistry classrooms. Among the main attraction are the “burn rooms,” where investigators can recreate fires from the tiniest scale to the massive.

“It can be as small as burning a small appliance — or we can burn a two-story house in here,” said John Allen, the facility’s director. “This is the largest investigative tool in the world.”

Four teams held a competition to see which could build the hottest fire: The goal was to reach “flash-over” temperature of 1100 degrees Fahrenheit the fastest.

Each team was given the same materials — some carpet remnants, a stack of chairs and some alcohol, and the same setting, a replica of a small room, hallway and a single window.

Resident Agent in Charge Steven J. Avato, who heads the arson and explosives team from Falls Church, joined a team of investigators from New Hampshire, Colorado, Florida, Georgia and Delaware who hoped to take home bragging rights for building the hottest fire.

“We have to understand how fires grown and move,” Avato said in an interview. “The reason is to try to test how well we understand what we have learned this week. It’s kind of an academic race.”

Avato and his team, which works from the ATF’s Washington Field Office, has investigated some of the biggest arsons and fires to burn through the Washington region, includings the fatal arson at Good Guys strip club in Northwest Washington in 2007 and the burning of a chapel at the grounds of the Virginia Theological Seminary in Alexandria in Oct. 2010.

Avato said investigators study not just how to chase arsonists but also how to determine whether fires are accidental.

“It’s not just who set a fire, but also if no one intentionally set a fire,” he said. “We really need to prepare to look at every fire scene with an unbiased eye.”

Back in the lab Friday, Avato’s team carefully stacked chairs and ventilated the “room” by punching holes in the drywall. They came in second — to Avato’s chagrin — in part because the air flow choked off the fire.

Still, the week of training is worth it. “If you want to get the best experience, this is the place to do it,” said Avato.

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