Flashpoint Notes

Why I Never Use Gasoline In the Shop

image link-topic-sf0.jpg

The "flashpoint" of a flammable liquid (or a few solids) is the temperature at which it will generate sufficient vapor above it such that any spark or source of ignition will ignite it. It is a very important thing to know when working with such materials.

The flashpoints of many common flammable liquids are more or less what one might expect. So for example the flashpoint of methanol (wood alcohol) is 55 degrees F. It is good to know that this is below normal room temperature. The flashpoint of kerosene is around 100 degrees F. The flashpoint of No. 2 Diesel is something over 125 F.

So what is the flashpoint of gasoline (petrol)? Negative 50 degrees F.

Yes, negative 50. Few people who don't spend their winters in the polar regions have ever seen gasoline that was not well above its flashpoint. At room temperature, gasoline is over 100 degrees above its flashpoint. The flashpoint of gasoline is approximately the same as the flashpoint of diethyl ether (a substance notorious for its flammability).

Gasoline is insanely dangerous.

There was of course an entire generation which grew up using gasoline as the universal shop solvent. This was even institutionalized (the composing sticks for my Ludlow caster often have "wash in gasoline twice weekly" engraved on them). Most of them got lucky and nothing happened; from this they tend to conclude that gasoline is safe. Not everyone gets lucky, however. Several years ago we wondered why there was a crowd of emergency vehicles sealing off part of our street. The guy was siphoning gasoline. We knew he had returned from rehabilitation a year later when they installed the wheelchair lift on the porch.

Quick flashpoint approximations:

About the images