Why is it likely for a car to blow up if its upside down like in a crash?

Question

Why is it likely for a car to blow up if its upside down like in a crash?

Answer 1

It isn't.

Gas tanks are placed where they are so it is unlikely that they would be punctured, even in the case of a rollover.

Gas tanks are made of materials that don't spark, so even if there were an explosive mixture of air and gasoline vapor in the tank, there is no reason for it to explode.

Gasoline does not explode until it is intimately mixed with air (i.e. essentially fully vaporized or with very fine droplets) so even a pool of gasoline would not explode (though it would burn nicely under normal circumstances)

In theory, if the tank were almost empty so that there was only a little bit of gasoline and mostly air and you could crate a spark or a sharp increase in its temperature (i.e. rapidly compressing the tank), then you might get an explosion, but even then, while it would total the car, I'd guess you'd still have a (wreck of a) car, and not just tiny pieces spread over the landscape.

BTW, many years ago now, Ford cut corners on the gas tanks in its Pinto. many people were hurt when the gas tank ruptured during rear end collisions. The results were fires:

http://www.fordpinto.com/blowup3.htm

And when Dateline MBC wanted to show an exploding gas tank, they had to rig it with explosives:

http://en.wikipedia.org/wiki/Dateline_NB...

Answer 2

While the dramatic explosions that one sees in films are an exaggeration, all of the ingredients for an explosion are there: the gas tank is upside down, and will sometimes leak even if it did not rupture in the accident. Of course, if it DID rupture,then fire and probably an explosion are very likely. The engine is usually still running and the electrics of the car are still on, so there is a chance for sparks to ignite the gasoline. Windshield wipers can easily be 'sparky', but so can electric fan motors. Of course, of the occupants are smoking ...

But car designers do make some effort to make a gas tank that will not so easily rupture or leak, and without gas, an explosion is not likely at all.