Rioters in France burned more than 1,400 vehicles on Sunday night, as the civil unrest that began almost two weeks ago continued to spread. So far, at least 4,000 cars and buses have been torched by angry protesters. How do you set fire to a car?
From the inside out. The car's interior contains all the parts that are easiest to ignite: carpets, seat foam, soft plastic, even windshield wiper fluid. Manufacturers treat the interiors of some cars with flame retardants, but even these vehicles will go up in flames in a few minutes if there's a bit of fuel around. A cigarette butt probably won't set off a blaze by itself, but a single sheet of newspaper, if ignited, could do the trick.
The easiest way to torch a car would be to crack open a window, douse the interior with lighter fluid, and toss in a match. If the windows aren't open or smashed, a car fire will burn itself out for lack of oxygen. (The heat, soot, and smoke from one of these contained fires will often total a car all the same.)
A fire in the interior of a car spreads quickly to the trunk. A bit later, it passes forward through the metal divider that protects the engine compartment. The divider—which is known, for some reason, as the "firewall"—has holes in it for the wires and tubes that provide air conditioning, heat, and power from under the hood. Once these tubes burn out, flames can get through the holes and into the engine. Within 10 or 20 minutes, the fire will have gone through the whole engine compartment, burning flammable fluids and melting plastic and metal components.
A fire that starts on the outside of a car is less likely to spark a serious blaze, unless burning fluid—from a molotov cocktail, perhaps—drips into the rubber door seals. Once those seals melt, the fire can get inside and ignite the passenger compartment. The rubber tubes and flammable liquids on the car's underside are also vulnerable to torching. (In a recent incident in Ohio, vandals allegedly lit up a car by piling American flags beneath it.) Fires that burn beneath a car could sustain themselves on nearby grass or dry leaves.
Once a car fire gets going, tires may start to blow. Heat inside the car can cause airbags to deploy suddenly and then melt into white goo. Pressurized struts pose the greatest danger to bystanders or firefighters—the cylinders that help pop open a hatchback or a hood can heat up and explode, sending rods flying dozens of feet from the car. Struts that normally provide shock absorption for the bumpers can also shoot out of the car.
Will a flaming car blow up? Not like in the movies. A car's fuel tank never creates the kind of explosion that sends people flying off their feet. Gas tanks are typically made of thick metal that can withstand a lot of heat, though their rubber filler tubes are susceptible to flames. A full tank may spill some gas when the tube burns out. When that gas ignited the fire would flare up—but it wouldn't burst with concussive force.
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