Gasoline is not flammable

[snopes]

Comment: I have heard from many different sources that gasoline (the
liquid) is not flammable. The vapors are highly flammable, and the
surface of the gasoline is flammable...the the liquid gasoline below the
surface is allegedly NOT flammable.

Most of the stories that I hear regarding this stem from people welding
inside of large gasoline tanks while the taks are full.

Normally, you would think that this is suicide...but each time I hear
about it...people tell me that gasoline is not in fact flammable until it
starts to evaporate.

Can you confirm this for me? Is it actually possible to weld inside a
full gas tank and not have it explode assuming that you stay clear of the
surface of the gas?

I believe that it is the vapor that burns but it would need to be pretty cold out for me to weld inside a full gasoline tank.

[DaGuyWitBluGlasses]

Simple:
any gasoline that's not on the surface is insulated from the oxygen in the air: breaking up the fire triangle.

[A Turtle Named Mack]

How is it that people are doing welding inside a tank filled with gasoline. Even if the stuff doesn't catch fire because of lack of oxygen (and the reason you are welding it, after all, is because it is leaking out to the air!), that has got to be one of the most noxious, cumbersome and poor visibility environments there could be. And you have to have oxygen tanks when you dive to weld, which sort of turns up the Risk Dial to OMG!

Kind of reminds me of the fact that wate, pure water, does not conduct electricity very well. If I was swimming in a pond full of distilled water and it was struck by lightning I would probably be fine. Now, how easy is it to find a pond full of distilled water?

And how easy is it to find a puddle of gasoline that is not giving off highly flammable fumes?

[Deepfrydegg]

Yes and No.

Gasoline below the surface is not flammable. Only because the top layer of Gas (that IS burning) is keeping the oxygen away from the lower layer. (like DaGuyWitBluGlasses said)

Gasoline vapor has a Lower explosive limit (LEL) of 1.4% (meaning when the atmosphere has 1.4% gasoline fumes, and a spark is introduced = Big BOOM!)
Conversely, the Upper Explosive limit (UEL) is 7.6% (meaning beyond 7.6% gas, there is not enough oxygen to support an explosion).
Additional problem with that UEL, most people would suffocate from lack of oxygen.
(all numbers provided by the National Institute of Occupational Safety and Health [NIOSH])

[DemonWolf]

This is one of those things that I accept as true, but will continue to behave as though it is false.

Basically, I will assume that all gasoline is flammable and keep it way from fumes.

[Silas Sparkhammer]

I've actually played with this. You pour out a pint of gas into an old frying pan, or hubcap, or whatever, and flip lit matches into it. About half the time, the match will splash into the liquid gasoline, hiss, and go right out.

But...not always.

DemonWolf has the right way of thinking about it. An ex-co-worker of mine had some cute scars over his chin and one side of his face from taking chances with gasoline. As Edgar Poe said, "Never Bet The Devil Your Head."

Silas

[jimmy101_again]

Originally Posted by DemonWolf

This is one of those things that I accept as true, but will continue to behave as though it is false.

Basically, I will assume that all gasoline is flammable and keep it way from fumes.

A prudent way to look at it.

The OP has kind of a poor choice of words. "I have heard from many different sources that gasoline (the liquid) is not flammable." By all defintions of the words "gasoline" and "flammable" gasoline is indeed flammable. But fuel isn't the only thing you need for fire.

The possibility of ignition beneath the surface of the gasoline is similar to the possibility of a flame being sucked back into a propane (or acetylene, or butane, or ...) tank used to fuel a torch. Even if the flame is sucked back into the tank there is no air (or other oxidizers) in the tank so the fuel will not burn.

So it is true, an ignition source below the surface of a pan of gasoline cannot ignite the gasoline.

[Silas Sparkhammer]

For what it may be worth, a bubble of air in a volume of gasoline also produces a flammable surface. Scientific American had an article on it. Researchers would introduce air-jets into liquid natural gas, or into gaseous natural gas, strike a spark, and produce a flame.

(Science fiction writer Poul Anderson proposed this in a story in which a human space traveller is lost in the atmosphere of Jupiter. He lights a "signal flare" by expelling some of his spare oxygen and igniting it in the methane-rich Jovian sky.)

Silas

[StewPot]

Originally Posted by snopes

Comment: I have heard from many different sources that gasoline (the
liquid) is not flammable.

This is TRUE! I just checked my gasoline can in the garage and it says in bold letters "Inflammable."

[Electrotiger]

"Don't worry, it's inflammable!"

On this topic, it was kicked around by a lot of boys in my elementary/middle school that gasoline liquid burned, and gasoline vapor exploded;

Therefore, if (for some reason) you wanted to blow up a gas station, you could light the end of a running gasoline nozzle on fire, and it would burn, but as soon as the gas ran out, the vapor would ignite, run backwards into the underground tank, and explode.

A CUNNING PLAN!

I know that the execution is pretty much all BS, but the concept of a gasoline tank exploding because of the transition from liquid to vapor when it "runs out" has always made me curious.

I've been half-tempted to send it to the Mythbusters.

[Silas Sparkhammer]

Originally Posted by Electrotiger

. . . the concept of a gasoline tank exploding because of the transition from liquid to vapor when it "runs out" has always made me curious. . .

It does seem kinda silly. It's a misapplication of the "intermediate value theorem." We know that a full gas tank burns. We know that one which has recently been emptied, and thus has a lot of fumes, can explode. But this doesn't mean that you get a smooth, continuous transition between the states, where the tank quietly burns down to a "critical point" where it is suddenly explosive, not having been so before.

If you take a full jerrican of gasoline out to the desert (sigh; I know, but I was young) and light it on fire, it merely burns. You get a flare-up as the burning surface increases, but no explosion.

If you tie a long rope to the can and tilt it over, the spreading pool of gasoline burns quite nicely...but no explosion.

(But...if you take a frying pan or hubcab, pour in gasoline, and then pour in a couple cups of black powder...and light it on fire...whoo hoo! NICE pyro!)

Silas (stand way back, y'hear?)

[matches]

This Link Seems to settle the issue.

When a flammable liquid is in its liquid state, it will not ignite. It will only burn when in its gaseous state.

I take this to mean that it's flash point is higher than it's vapor point, meaning that that when heated it will go to vapor before igniting, as such liquid gasoline is not flamable, but once exposed to flame it likely will become vapor and will ignite. Hence don't have an open flame around gasoline, the vapors coming off of it will burn, and the heat from that will turn more liquid gas to vapor, which will then burn, and so on and so on.

[Troberg]

I take this to mean that it's flash point is higher than it's vapor point, meaning that that when heated it will go to vapor before igniting, as such liquid gasoline is not flamable, but once exposed to flame it likely will become vapor and will ignite. Hence don't have an open flame around gasoline, the vapors coming off of it will burn, and the heat from that will turn more liquid gas to vapor, which will then burn, and so on and so on.

Exactly. Gasoline gives off a lot of vapors (hence the smell...), so even though it's picky about air/fuel mixture, there will be a bunch of vapor ready to ignite somewhere around liquid gasoline.

Some loosely related info: During WW2, some Soviet aircraft used a neat fire supression system for the fuel tanks that was as simple as it was ingenious. Some of the exhausts were led into the tank, which meant that there was very little oxygen, and little risk of fire, even if penetrated by bullets or if flames from an engine misfire followed the exhausts into the tank. I don't know if they used it, but some extra pressure could probably help the fuel pump a bit as well.

The system was both more effective and much lighter than the self sealing tanks that most other nations used, which consisted of a dual layer tank with some liquid between the layers which turned into a rubbery gunk when exposed to fuel.

[Etienne]

Originally Posted by Troberg

Some loosely related info: During WW2, some Soviet aircraft used a neat fire supression system for the fuel tanks that was as simple as it was ingenious. Some of the exhausts were led into the tank, which meant that there was very little oxygen, and little risk of fire, even if penetrated by bullets or if flames from an engine misfire followed the exhausts into the tank. I don't know if they used it, but some extra pressure could probably help the fuel pump a bit as well.

The system is commonly used on modern tankers - We call it inerting. The only problem I can see about using it on a plane is that exhaust is hot and dirty - Onboard a ship, you'll have IG scrubbers (A sort of multi-tiered water fountain that'll clean and cool the exhaust gas) and various non-return system, to prevent any hydrocarbon vapors from being sucked back into the engine spaces (Yikes!)

That's some pretty heavy and voluminous equipment... That the soviet would have had to find a way to fit on a plane, unless they had an engine that could run with soot in the fuel. :-D

And you're right, the added pressure does help with pumping. It's not a great difference in the grand scheme of thing, but it does help somewhat. (Since tanks have to be kept at an higher pressure than the atmosphere, to prevent the entrance of oxygen...)

As for welding inside a tank with gasoline, or any kind of flammable liquid or vapor, that's a huge no-no in the marine industry. Even if the tank is inerted - An inert atmosphere can't support life, and welding with an SCBA on can't be fun.

And yes, I've also throw a match in a puddle of #2 diesel and watched it fizzle. I wouldn't use the stuff to put out a fire, tho :-D I've been told that even LNG (Liquefied Natural Gas) is entirely unflammable in it's liquid form.

Anybody wanna try? :-D

Etienne

[Troberg]

That's some pretty heavy and voluminous equipment... That the soviet would have had to find a way to fit on a plane, unless they had an engine that could run with soot in the fuel. :-D

My guess is that they just used a filter, as they don't need the exhaust to flow past the fuel, they just need to borrow some of it and keep the pressure up.

I've been told that even LNG (Liquefied Natural Gas) is entirely unflammable in it's liquid form.

Liquid propane is unflammable, and that's pretty close. When used in jet engines, a good injection nozzle for atomization is necessary, or in some cases the feeding tube is coiled around or in a hot part of the engine, boiling it to a gaseous form before entering the combustion chamber (which also have the nice side effect of increasing pressure, giving a nice spray).