Fire fighters in Canada put out gasoline car fire.
In 2006, US fire departments responded to 278,000 gasoline vehicle fires that took some 500 lives.

Can Electric Cars Explode?

EV World's Technical Editor explains why electric cars won't explode.

By Michael Brace

Of all unknowns that we deal with on a daily basis, this one question seems to be gaining in popularity as more and more people come to the realization that a lot of the personal transportation vehicles of tomorrow will not be fueled by gasoline

But if we start cruisin’ down the road via electrons, just how safe is it? What happens in an accident? What if it’s a nasty one!?

We all seen exploding cars on TV but most of have not seen too many in real life, so for the most part we are all comfortable knowing that unless we plunge off a 100-foot cliff chances are our car isn’t going to explode. But what if it’s electric?

From a ‘physics’ stand point you need two things to happen simultaneously to produce an explosion: A rapid expansion of a gas, and the means to contain it for a brief instance in time. How rapid the gas expands and how brief it is contained determines the strength of the explosion. More often than not that rapidly expanding gas is a caused by a fireball.

But it’s still not an explosion until you try to impede its expansion. To do that you need an enclosed structure around the fireball that suffers catastrophic failure at some time before the gas finishes expanding. That brief interruption allows the expanding gas to reach pressures so immense as to cause structural damage when they are allowed to continue expanding by destroying the container and all around it (think ‘pipe bomb’ here).

Most of the ‘explosions’ that you see on TV (or at the movies) are not explosions at all but just large, unimpeded fireballs set off by small tiny explosions. A lot of heat and fire for sure, but not much damage to anything fireproof around it. But it doesn’t have to be a fireball at all to cause an explosion.

Remember the movie Jaws? Remember what happened when Roy Scheider shot the SCUBA tank in the sharks’ mouth? And it was just full of plain ol’ air. But ask any SCUBA diver why they don’t drive around with their SCUBA tanks in the trunk of the car and you’ll learn that even compressed air alone can blow a car completely in half.

But I digress; back to those exploding cars...

For the most part gasoline-powered cars use their fuel to create a lot of little explosions all contained with in the piston walls of the engine. The pistons then use these explosions to create rotary motion and the car rolls on down the road. Electric cars do not use explosions or heat to create rotary motion; rather they run electricity through copper wires to create powerful magnetic fields to turn the electric motor. (The small amount of heat that does build up in an electric motor is from the resistance of the wires in the motor to the electricity passing through it.)

Most of us know that electricity can be used exclusively to create heat through resistance (think ‘stove top’ here) or heat through a spark (think ‘lightening’ here), but electricity does not make a very good fireball unless it is near something very flammable, like gasoline (for instance). And even though pure electric cars don’t usually carry gasoline around they do carry a lot of electricity around in the form of batteries.

Which brings me back to the original question: Can electric cars explode? Answer: Not really...and definitely not as easily as a gasoline powered car.

In 2008 a Toyota Prius converted by Hybrids Plus caught fire due to a faulty connection in the aftermarket battery pack.

If the batteries in an EV are stored in a very strong, virtually airtight enclosure AND if they caught on fire in a very rapid manner they could explode. However, knowing this EV engineers try to do just the opposite. They locate the batteries in an open framework (or structure) that allow the batteries to dissipate the small amount of heat they generate during high discharge rates (think ‘pedal-to-the-metal’ here) yet still protect them from a catastrophic impact (think ‘head on’ here). Worst-case scenario is that the batteries cannot dissipate this heat by normal means (think ‘broken radiator’ here) and they go into thermal runaway. Thermal runaway is when the batteries are shorted out causing a massive amount of overload current (think ‘touching the terminals together with a wrench’ here). This overload current can create enough heat to ignite anything near it, including metal. Then you can get a fire; not a fireball, just a fire.

Gasoline-fueled cars cannot stop the accidental discharge of gasoline due to an unplanned fuel leak (think ‘rollover‘ here), so naturally they run a very high risk of an unwanted fireball anytime one occurs. Electrically powered cars can have the same problem (think ‘short circuit’ here), however they can avoid the fire by using something as common as a circuit breaker. It also surprises most people to hear that many of the batteries being designed into modern EVs are completely sealed and virtually fireproof, even when punctured with a sharp metal object.

In summary, any vehicle of any type can explode given the right set of circumstances, but you still need those two components for that to happen: a rapidly expanding gas and a sealed case to hold it in; of which EVs have neither.

Times Article Viewed: 16310
Published: 07-Feb-2009


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