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McCarthy teams up with other fire investigators to find out how fires start and how they spread.
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Melissa Golden / Redux
Fire Starter
Lee McCarthy sets fires to help crack arson cases

By Sara Goudarzi | for Science World

Lee McCarthy’s job is a hot one: He sets furniture, cars, and even whole buildings on fire—then he uses science to study how they burn.

As a fire-protection engineer for the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), McCarthy teams up with other engineers and fire investigators to find out how fires start and how they spread—both in the lab and out in the real world.

Sometimes, McCarthy’s investigations find that a fire was accidental. Other times they uncover a crime.

When did you decide to make studying fires a career?
I became interested in fires when I volunteered as a firefighter in high school. In college I studied engineering because I wanted to learn how things worked. Later, I combined my interests by earning a degree in fire-protection engineering.

How do you study fires in the lab?
The ATF has a large fire research lab in Maryland, just outside Washington, D.C. We’re constantly running experiments there, basically re-creating fires.

We can burn a bus—or even a two-story building—underneath an instrument that captures smoke with what looks like a stove-top exhaust hood. The instrument, called a fire product collector, allows us to gather information on how much energy the burning objects release. An object that burns with a lot of energy spreads the fire quickly. The instrument also tells us what chemicals and particulates are in the smoke that’s released.

With our specialized tools, we can also measure the toxic effects of fires and see how much heat a fire is giving off. All of these things teach us more about a particular fire and how it behaves.

Why is it important to study fires in the lab?
Up until the late 1980s, fire investigation was more of an art than a science. But then scientists and engineers started being called to difficult fire scenes to help figure out the sources of the fires. Now engineers routinely visit fire scenes. We use what we’ve learned in the lab to help determine how or where a real-world fire started.

This is especially important in criminal matters. In these instances, we’ll testify in court about our analyses as they relate to a case. Our testimony can help get those responsible off the street.

Tell us about one of your most interesting recent cases.
There was recently a fire in a two-story shed in South Carolina where someone died. After examining the fire scene and taking witness statements, investigators identified three items at the scene that may have ignited a fuel spill and accidentally caused the fire: a weed whacker that had been used recently, a paper shredder, and a cigarette.

Back in the lab, we built a shed just like the original and conducted more than 100 experiments to see if any of those three items could have caused the deadly blaze. We concluded that none of them were likely ignition sources. Based largely on our results, investigators decided that the fire was set intentionally, and a suspect was later charged with arson and murder.

What do you like best about your job?
I get to travel all over the country to investigate major fire scenes. When I’m not traveling, I’m in a state-of-the-art lab watching and understanding how fires burn—sometimes with 15-meter (50-foot) flames reaching the ceiling in our burn room. You can’t get that kind of experience anywhere else!