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We've all seen the movies: Rambo runs over one of the terminals at a gas station, freeing the flow of gasoline to the street, the gasoline finds its way under a military vehicle, and the vehicle violently explodes, presumably from the gas in the gas tank. Is this actually possible/likely?

I remember hearing somewhere that gasoline in a liquid form isn't flammable; it's really the vapors that are flammable. Besides, isn't something being flammable much different than being explosive?

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    Didn't Mythbusters do an episode on this? – JasonR Apr 13 '11 at 17:32
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    There are also videos on YouTube of talking unicorns. I'd like to hear an explanation and how this works. – Naftuli Kay Apr 13 '11 at 20:01
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    Heat applied to a sealed container will drive the pressure up. Get it hot enough you could burst a seam, spewing the contents into the (hot!) environment. Limiting parameters depend on a lot of things. – dmckee Apr 14 '11 at 2:51
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    Gasoline vaporizes at 47 F degrees. Gasoline will ignite on its own at 564 F deg. It is safe in vented, full contained rather than a almost empty one. Store in shaded areas, out of direct sun light. – user14483 Jul 7 '13 at 17:37
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    Tanks of gasoline are not always full. In fact, half the time they are half empty - which pretty much implies the rest of the tank is filled with gasoline vapour. – DJClayworth Jun 1 '14 at 3:30
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Yes, tanks of gasoline can explode, given the right conditions.

The Quebec town of lac Megantic was recently flattened by a number of huge explosions from derailed cars carrying light crude. (And not big-flamey-Hollywood explosions but kill-hundreds-of-people explosions). One of the reasons given for the explosions was that the "oil was more volatile than previously thought, having characteristics similar to unleaded gas".

On a smaller scale, there have been warnings published about the explosive capabilities of ordinary gas cannisters.

Other incidents include this, this, number 4 here and this.

As to whether the traditional Hollywood method of ignition, firing a small calibre handgun at an inches-thick metal tank would cause such an explosion, I'll leave that for another question.

5

Gasoline needs to be combined with an oxidizing compound, such as oxygen in air to explode.

Gasoline vapors mixed with the correct amount of air will explode.

At atmospheric pressure and room temperature (except for a spark), gasoline/air mixtures will explode if the percent by volume gasoline is between 1.2% and 7.1%.

See https://www.mathesongas.com/pdfs/products/Lower-(LEL)-&-Upper-(UEL)-Explosive-Limits-.pdf

Also, the definition of a flammable liquid is that the liquid is flammable if at a temperature of 100 degrees F a small flame about the liquid will ignite the vapors above the liquid.

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As you note, the flammability limit requires a mix of fuel and oxygen (mostly oxygen) in order to have a fire, and that means that there's only two ways in which this can happen, and neither really fit your scenario:

  1. The container actually has to be almost empty so that it's filled with a mixture of a lot of air, and a very small amount of fuel, most of it in vapor form. Then you have ideal conditions for an actual explosion and all that's missing is the tiniest of sparks. This is what caused the crash of TWA flight 800, and can be prevented by special inerting systems or tank designs.
  2. Or the container has to sit in the middle of a major fire (possibly started by a leak) for quite some time (think 10 minutes at least). Then the heat can cause the fuel to expand and increase the pressure so much that the container bursts. When that happens, the sudden release of pressure will allow a large amount of hot fuel to almost instantly vaporize, mix with the surrounding air and then ignite in a huge flash flame or fireball. Pretty much all the examples in the answer by DJClayworth shows this case quite spectacularly.

Simple leaks of fuel can cause a fire, but not an explosion, though of course the fire can eventually lead to scenarion no. 2.

The central argument of this answer is theoretical in nature. We do not allow answers based uniquely on common sense or pure logic. Answers which are wholly based on a theoretical model are generally downvoted and may be deleted. See FAQ: What are theoretical answers?

  • This looks quite reasonable, but this site requires citations. I count three important facts. Your two scenarios, and the claim that they are exhaustive is the third. – Brythan Mar 29 '17 at 22:59
  • Please provide some references to support your claims. – Oddthinking Mar 30 '17 at 5:38
  • @Oddthinking: I hope it's better now. – Michael Borgwardt Mar 30 '17 at 7:44
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In a closed and rigid/strong container an explosion will occur.

In a soft container (like the Hindenburg)(whether gas or liquid) it will burn at the edges.. where there is air/oxygen.

In a long tube, like an 'empty' pipeline (gas or vapor + air, not full of liquid or 100% gas), there will be a fire until the speed of the blaze exceeds 'sonic' speed. At that point the gas/air will be compressed for several feet in front of the fire and that compressed pocket will explode, rupturing the pipeline. Then the pressure drops and the fire resumes, traveling down the pipe... The result is a timed series of explosions in the pipeline at specific distances. The distance between explosions can be predicted from the size of the pipe and the flammability of the liquid vapor (or gas). The cure is to put screens across the pipe at those predicted explosion distances (or less) so the fire is cooled and stopped before the (next) explosion can occur.

Ref: Flame arresters: https://en.wikipedia.org/wiki/Flame_arrester http://www.enardo.com/pdfs/tech_paper_fat.pdf

Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

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