Projectiles and toxic gases
But no kaboom! What happens when a car goes up in flames
hen cars burn, as they
did so often in Paris
this month, the
flames aren’t the biggest danger to people standing nearby. What you really need to watch out for are those supports on hoods and hatchbacks — the ones made with compressed gas cylinders.
“ I’ve seen those explode right through the vehicle and shoot out the other end. You can be impaled on those,” says James Bennett, a fire protection engineer with the Ontario Fire Marshal’s office, which tracked 4,256 vehicle fires in 2004 that caused 81 injuries and seven deaths.
In fact, there is a lot more than dramatic news footage to a burning vehicle. The mix of fluids, compressed air, and an increasing amount of various plastics in modern cars all combine to create an explosive, projectileshooting morass.
Bennett is on intimate terms with what fire does to a car. Before working for the province, he was an insurance investigator,
Wa job that involved a lot of burned- out hulks.
In a laboratory test, Bennett once saw a burning cylinder shoot almost 10 metres. Watch out for the burning bumper, too.
“ There’s a shock absorber built into the bumper for when you run into something, to absorb the impact,” he says. “ Those can explode and cause the bumper to shoot forward.” Bennett says these propulsive bumpers have injured firefighters. The amount of steel in new cars is diminishing. A lighter car means greater fuel economy, but the more plastic and fibreglass packed into a vehicle, the more the flames can devour.
“ Interior trims,” says Bennett, as he lists the flammable parts of a car. “Seats are usually constructed with a polyurethane foam ( that burns).” The tires are combustible. And there are combustible fluids within the vehicle, like engine oil and power- steering fluid.
“ Some vehicles use fibreglassreinforced panels for hoods, fenders, and exterior door skins,” all of which, Bennett says, will burn.
“ In France, that type of combustible material is accessible on the exterior of the vehicle, so you don’t even have to break into the vehicle to light it on fire.”
It can take 20 to 30 minutes for a fire to pick a car clean, Bennett says. In the end, all that’s left is a blackened steel frame, sometimes the doors and trunk, and bits and pieces of the engine. And if the flames don’t get you, the toxins might. Burning cars release hydrogen cyanides, says Bennett. “You get all kinds of things from ( burning) plastics. Poisonous gas. Hydrocarbons. Carbon monoxide.” When you torch a car, “ not only are you putting yourself at risk, you’re putting everybody else at risk. . . ( The rioters) are causing damage to the environment.”
Bennett also deflates the Hollywood scenario where the hero drags someone from a burning car seconds before it explodes in a giant ball of fire. It’s a myth — gas tanks, he says, don’t explode.
“ A lot of people, when they report a car fire, say they hear explosions. Usually the loud bang is tires blowing.” As for the gas tank, “ It’s not the fluid that ignites, it’s the vapours that come off the fluid that burn.”
In a car crash, the fuel tank will puncture, Bennett says. Vapours get free. They’re heavier than air, so they hover at ground level, moving around the crashed car. All that’s needed is a spark or an overheated car component to ignite the vapours, and you’ve got fire everywhere.
“ That’s very hazardous to the people inside.”