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I see this a lot in movies. Have anyone studied whether this is easily doable?

Shog9
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Louis Rhys
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    Mythbustered tested it and it didn't work. Like the linked duplicate answers: the air-gas mixture isn't right for an explosion. – Martin Scharrer Apr 19 '11 at 16:51
  • Needs more details. "Fuel" is a very generic term. Are we talking gasoline? Propane? Rocket fuel? Is it compressed? Is it liquid or gas? etc. – Jason Plank Apr 20 '11 at 05:25
  • possible duplicate of [Would a large quantity of gasoline in a closed container explode violently when exposed to fire?](http://skeptics.stackexchange.com/questions/2093/would-a-large-quantity-of-gasoline-in-a-closed-container-explode-violently-when-e) – Kit Sunde Apr 20 '11 at 09:19
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    @Jason Mythbusters also shot a variety of propane tanks in a separate test - they couldn't get one to explode, even when using incendiary ammunition. – John Lyon May 06 '11 at 05:42
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    In order to "explode", fuel must be mixed with air in proper proportion. That's what happens in your combustion chamber.... A fuel tank of almost any sort normally has a quantity of liquid fuel and a relatively similar quantity of air...Nowhere near the right proportion for ignition. As well, unless one is using dedicated incendiary or tracer ammunition, there's nothing in a normal projectile to cause ignition. – M. Werner May 13 '11 at 15:56
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    @M. Werner: But for overheated partially-empty tanks, the ammunition might work just for rupturing the tank, initiating a [boiling liquid expanding vapor explosion](http://en.wikipedia.org/wiki/Boiling_liquid_expanding_vapor_explosion), correct? Unlikely for a car fuel tank (as the excess pressure would much sooner pop off the refuelling cap), but maybe for a larger storage tank (but then you'd need a *cannon*, not a handgun - might make for an *even cooler* action movie though ;) ). – Piskvor left the building May 18 '11 at 22:09
  • There is a mythbusters episode on fuel myths where they attempt to do this without success. You need a fairly precise fuel air mixture to get ignition. Hollywood is largely to blame for this myth. – Tjaart Jun 25 '12 at 15:11
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    Interesting, that in movies diesel cars also explode ;-) – vartec Oct 26 '12 at 09:29
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    @vartec Yeah--when the reality is that I saw someone with a plastic can of diesel who managed to light it on fire. The fire peacefully burned above the can, didn't even melt it, didn't do anything to the person carrying it (and who was showing it off for several minutes.) – Loren Pechtel Jul 10 '14 at 23:56
  • I just got done with a fun day of shooting, we had a bowling ball cannon which damaged a car pretty good, then while shooting it up with three other buddies, all with rifles, I was surprised that the car actually did ignite (not explode). Guessing the fuel tank was hit, and then a subsequent full metal jacket caused a spark. –  Nov 15 '15 at 04:18
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    Note that the official conclusion about the crash of TWA flight 800 is that an almost-empty fuel tank exploded after being ignited by a short circuit. Jet fuel is essentially the same thing as diesel fuel. Given the right air-to-fuel ratio, all it takes is a tiny spark or sufficient temperature to cause an explosion. – Mark Nov 16 '15 at 02:17

2 Answers2

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I'm not sure if this is considered a good enough source, but in Season 3 Episode 2: "Scuba Diver and Car Capers" (free if you have Amazon Prime), the Mythbusters tested this:

The Discovery Channel TV show MythBusters tackled this question in a 2004 episode, shooting five bullets into the gas tank of a Cadillac. There was no explosion, not even a fire. This raises the question of how a bullet would cause an explosion in the first place. To ignite gasoline, both heat and oxygen are required. If there's insufficient air in the tank, an explosion won't be possible, though an empty tank would be more likely to explode than a full one. And while a bullet is heated by the explosion that propels it, the bullet itself won't necessarily be hot enough to ignite gasoline.

I remember seeing the episode, and they seemed to do a reasonable job testing it, using various fuel/air mixtures to see if they could get it to work.

They also tried tracer rounds in a "Mythbuster's Revisited" episode, and also didn't manage to make it explode:

It has already been proven that when shot by a normal bullet a gasoline tank will not explode. However, if a gasoline tank is shot by a tracer round from a great enough distance so that the round can ignite with air friction, it will cause the gasoline to catch fire. By the time this happened the tank was so riddled with bullets (from previous tracers that were fired too close to ignite) that there was no contained pressure, but the MythBusters surmised that had the tank been properly enclosed, it may have exploded; but overall it remains extremely improbable.

So, it's possible to ignite gasoline with tracer rounds, but really hard to get the tank to explode, since it loses pressure too fast.

That doesn't mean it's impossible, but the Mythbusters (who specialize in blowing things up) weren't able to do it on purpose, so it's definitely not "easily doable".

Brendan Long
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  • I'd highlight the *it's not impossible* part. Igniting fuel-air or gas-air mixtures can be notoriously finicky, but please don't take the Mythbusters failure to do so in a couple of tries as evidences that it will never happen. It probably won't, but don't try anything stupid... ;) – fgysin Nov 16 '15 at 07:36
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    @fgysin The question didn't ask if it was possible. They asked if it was easily doable (to which the answer is "no"). – Brendan Long Nov 16 '15 at 15:52
  • Because I love Fermi estimates: A car gas tank might be what, half a meter squared by some smaller height? The bullet will probably be moving at anywhere between 100 and 1000 m/s at the moment it penetrates the tank wall, depending on the type of firearm, type of bullet and distance involved. In other words, it will move through the tank in anywhere between 1/200 and 1/2000 of a second. I don't think that's enough for even a really hot object (say 1000 K) to cause any significant temperature increase to the liquid fuel it is passing through. And I'm pretty sure a bullet is well below 1000 K. – user Mar 31 '17 at 14:26
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The Insultingly Stupid Movie Physics also did an analysis of this trope:

Can a Handgun Bullet to the Gas Tank Blow up a Car?

The mixture in a gas tank is typically too rich to explode and this alone precludes the oft repeated shoot-the-gas-tank-blow-up-the-car scene. Furthermore, copper jacketed lead bullets are not good spark producers, hence, not good igniters but what about a steel jacketed or steel core bullet hitting that one in a million gas tank that is so close to empty it does have an explosive mixture in it?

When a piece of steel is ground, it emits a shower of yellow orange sparks--tiny particles of superheated metal. Judging from the yellow orange color the particles are over 1000 °C, certainly above the auto ignition temperature of gasoline air mixtures.

We donned safety gear and poured a small quantity of gasoline in an aluminum pie pan—just enough to wet the bottom. Using a pneumatic grinder on a bolt we showed [sic] the pan with sparks. The result: nothing. We dropped in a lit match and poof—flame.

Okay, no number of experiments can ever prove that grinding sparks will never ignite gasoline. There's no way to test all possible conditions. Grinding near gasoline is dangerous, but it's also clear that grinding sparks aren't a reliable source of ignition.

We didn't test bullets, but it's doubtful that one, particularly a handgun bullet, will reliably set off gasoline fumes.

The above experiments were conducted in a safety conscious manner under the supervision of a qualified professional. Do not attempt them on your own.

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Some Guy
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