Putting out fires with gasoline

[snopes]

Comment: I heard that, years ago, firefighters used to use gasoline to put
out cotton bales that had caught on fire. The theory was that the cotton
bales were packed so tightly that water couldn't penetrate the fibers,
whereas the chemical composition of gasoline allowed it to penetrate the
fibers. However, since the cotton was packed so tightly it wasn't able to
combust. The liquid, so the theory goes, would douse the fire.

[A Turtle Named Mack]

While one can conceivably extinguish a fire with sufficient gasoline applied sufficiently quickly (and best of all without any vapors being emitted, since it is the gas vapors that burn), it is fairly difficult to do as a practical matter. To do so, you have to deprive the fire of oxygen long enough for the surfaces to cool below ignition temperatures without any gas vapors combusting. But for this claim, more important is that water is a much smaller molecule than any of the various molecules that make up anything we would call gasoline. It could therefore penetrate almost any tight place better than gasoline.

A possibility is that a gas was used, such as pure nitrogen or carbon dioxide, which could be used to deprive the fire of oxygen and allow the fire to go out. Someone then could have heard that 'gas' was used to put out fires and thought that 'gasoline' was meant.

[Lachrymose]

Those firefighters = cat people?

[jimmy101_again]

Originally Posted by A Turtle Named Mack

But for this claim, more important is that water is a much smaller molecule than any of the various molecules that make up anything we would call gasoline. It could therefore penetrate almost any tight place better than gasoline.

The size of a molecule would have little to do with how well it penetrates a macroscopic packed object like a bail of hay. Gasoline has much lower viscosity and surface tension than does water and will be absorbed by many substance much quicker than water. If you want water to soak into something quicker you add a surfactant (like a soap) to lower the surface tension. Gasoline doesn't need a surfactant to penetrate into things quickly.

[A Turtle Named Mack]

Originally Posted by jimmy101_again

The size of a molecule would have little to do with how well it penetrates a macroscopic packed object like a bail of hay. Gasoline has much lower viscosity and surface tension than does water and will be absorbed by many substance much quicker than water. If you want water to soak into something quicker you add a surfactant (like a soap) to lower the surface tension. Gasoline doesn't need a surfactant to penetrate into things quickly.

Good point. Still because you do not want a vapor/oxygen combo to be exposed to an ignition source, you would have to have the dousing done quickly enough to exclude all air almost instantly. A packed bail of hay or cotton is very dense, but still would contain quite a significant amount of air.

[Gayle]

Cotton bale fires are weird things. They will combust. I can see the average gin hand throwing gasoline because sometimes they want to do a fire break to avoid all the other "bales".

[dreeness]

It sounds like a bit of a dodgy plan. Maybe the gasoline would turn the cotton bale from something like a big tinder-bundle into sort of a "soaked wick", like the surface would flare but then the rest of the cotton would be sopping wet with gasoline, and couldn't burn without air? Like a rag torch, maybe. Charred on the outside but soaked on the inside, maybe. But what if the bale was already so hot that it boiled the gasoline, it might just make a big cloud of vapor.