Playing with fire [Grand Forks Herald, N.D.]
Aug. 12--"This is the cool part," the stout fellow in cargo shorts and a T-shirt with an insurance company logo says to whoever was listening.
He has his little digital camera ready for action, pointing in the direction of a plywood shack with chicken wire across the front. Inside the shack is a mattress, an alarmingly large collection of old but not yet empty aerosol cans and a trail of lighter fluid and nail polish remover.
The chicken wire is to prevent exploding aerosol cans from whacking bystanders like our man with the camera, because, by golly, this really is going to be good. Who, in his heart of hearts, hasn't wished he could defy those warning labels that say do not dispose in fire?
It seems that fire investigators, insurance company adjusters, firefighters -- the people that regularly see firsthand the damage that fire can do -- they enjoy explosions and big fires like everybody else.
The scene is Grand Forks' firefighter and police training center, the time is Thursday morning in the middle of a 2 1/2 day, intermediate-level fire-investigation seminar hosted by the city.
Lessons range from electrical fires to flammable liquids to things that can accidentally explode to things rigged to explode, like bombs. Some are in the classroom and some live demos, giving everyone a chance to get some fresh air and inhale the fresh smell of burning urethane.
Fun and games
Jamie Novak, one of the instructors and a fire investigator with the St. Paul Fire Department, said the point of lighting aerosol cans on fire is to familiarize investigators with what that's like. Sometimes in the course of an investigation, they may hear neighbors talk about explosives when it might well have been aerosol cans or car tires popping, he said.
Novak makes sure everyone is standing far enough away, behind the hose by the fire truck, before applying the butane torch. If you ever want to start a campfire in 30 seconds, the recipe includes nail polish remover and plywood.
Three or four minutes in, the first of the cans cooks off. KABOOM! It was such a sudden assault on the ears that if this were a war movie, the camera would be shaking to demonstrate just how crazy loud it was. A 6-foot cone of fire shoots out of another can before it expired in similar fashion. Then there was another explosion and another.
You see afterward that most of the cans had burst along the side seam.
One of the cans has a little more grit than the others. It breaks through the chicken wire, flees the scene in a blur and runs smack into the head of the man with the camera, who had prudently moved closer to the cover of the fire truck. There's now a red circle on his left temple where the edge of the can had cut him.
He's still grinning as the firefighters check out the wound. Someone gives him the Painter's Touch can that walloped him and he holds it like a trophy, showing it off to the other students. The cap had blown off and the expanding hot gas had nowhere to go but thrust through that hole, which is pretty much the principle behind rockets.
Besides giving students first-hand experience with the sounds of burning aerosol cans, the demo also showed them the damage: There are now several gaping holes in the charred plywood.
"That was pretty spectacular," a fire investigator from the Fargo Fire Department thinks out loud.
Looking at patterns
It's not all fun and games, of course.
Fire investigation is serious business. Knowing the cause of a fire can help prosecutors go after arsonists, alert the public to potential dangers in their homes and tell insurers if they're liable for damages or if some careless appliance manufacturer is.
And to know the cause, you have to be familiar with the different kinds of fires.
"That's what this seminar's all about: What patterns are left after a fire," says Karl Nesler, an instructor and State Farm Insurance special investigator from Fargo.
He points to a pallet with laminate flooring nailed on top. On one side is a big smear of soot with a curiously clean line through the middle, like a fat python crawled by and wiped the soot with its belly. On the other side is a slightly sooty line, like a python in need of a bath came through.
The first line was a line of gasoline.
The gasoline itself doesn't really burn so where it was poured, the floor stays clean, Nesler said. Instead, the vapor from the gasoline burns, and, because it burns dirty, it leaves lots of soot, he said, which is why there's a blackened flare around a clean area.
The other line was denatured alcohol, the sort of thing you might find in paint cleaner, he said, and that stuff burns pretty clean leaving just a light layer of soot.
Knowing the traces that flammable liquids leave behind allows investigators to ask important questions, he said. If gasoline was burning in the living room, he said, one has to ask what it was doing there.
Nesler points to another pallet with a piece of plywood on top. Something had burned a hole right through it, leaving more soot all around.
A terry cloth rag soaked in linseed oil had been left there to dry. The thing is, linseed oil heats up intensely in the presence of oxygen, and the fuzzy cloth had given it plenty of surface area to oxidize and, at the same time, served as thousands of tiny wicks.
Three different causes of fire, three different patterns.
Two house fires
Here are two more patterns:
Before the house-of-multiple-explosions demo, there were the couches-on-fire demos. Two similar plywood shacks are outfitted like living rooms, each with a couch, an easy chair, an end table and a lamp. One shack has no windows and, halfway through, the door is closed, the other is wide open and has some rags and an easy chair a few feet away from the door.
Why, you ask?
Fire loves oxygen like an alcoholic likes alcohol; the more oxygen it consumes the wilder it gets. The less oxygen, the more depressed it gets before going away altogether. So, the shack with the open door is going to burn wild, and even the easy chair outside of the shack won't get away undamaged.
In fact, it didn't take more than five minutes before fierce yellow flames filled the open-door shack and the temperature gauge inside was reporting 1,400 degrees at the ceiling level. Students and instructors gathered in front to watch had already backed away and kept going as flames gushed out the door, singed the rags and made the easy chair smoke.
At 2,175 degrees, the windows abruptly shattered; a sign for waiting firefighters to snuff the fire.
The fire in the other shack was allowed to grow to the size of a bonfire, and the temperature reached 570 degrees before the door was closed. Just as quickly, the fire sputtered, the temperature dropped, and all was dark inside. When the door was opened, a dirty, brown smoke poured out.
The damage here was limited to soot, smoky-colored drywall and a corner of the couch where flames had feasted on the foam padding.
If your house is on fire, you might do well to close the door after you escape, Nesler said as an aside.
The inside of the open-door shack was a wet, blackened mess. The couch and easy chair were just frames, the urethane-filled cushions having vaporized into an oily, acrid aroma that clung to each nostril hair.
Nesler noted the black triangle around the door where the flame fanned out from the inside. Following that pattern, he pointed to some fabric on the right side of the couch and on the adjacent easy chair, all signs that the fire started on the left side, which indeed it did.
Though most of the students this week already have some fire investigation training under their belts, Nesler said regular training is important because the field keeps changing as investigators learn more about how fires behave. Not long ago, people thought concrete spalling could only be caused by flammable liquids, he said, but now they know that any fire could do that under the right conditions. That's the difference, he said, between arson and an accidental fire.
Reach Tran at (701) 780-1248; (800) 477-6572, ext. 248; or send e-mail to [email protected].
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Copyright (c) 2010, Grand Forks Herald, N.D.
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