Message text written by Randall Young
>No, it just has to be mixed with an oxidizing agent. Gunpowder for
instance
>burns very well when not a gas. So does almost any flammable dust (flour
>and coal being two common examples). Pure carbon does not vaporize first
>even when you burn a solid piece of it in air.
That's not what I was taught in highschool science class. But whatever.
>Gasoline vapors are only flammable in a fairly narrow range of gas/air
>mixture (which is why we have carburetors <g>). Pure gasoline vapor will
>not burn, except along a surface exposed to air.
In the trade this is called the upper explosive limit (UEL) and lower
explosive limit (LEL). I forget the exact numbers but gasoline will burn
over a narrower range than other flamable gasses such as propane. The
numbers for gasoline are somewhere in the vicinity of 12%LEL and 20% UEL
(these are concentrations by weight using air which is 20% oxygen. If
using pure oxygen adjustments must be made). Concentrations above the UEL
and below the LEL will not support combustion. In a gasoline fire there
are strata (is the singular "stratum?) that range from pure gasoline vapour
to pure air. The flame front will appear at the point where enough air
mixes with the gas vapours to bring the concentration down below the UEL.
Typical fire fighting techniques deprive the mixture of air (oxygen)
causing a ceasation of combustion.
When dealing with a propane leak where no fire has started yet (but is an
explosion hazard) the recommended procedure is to introduce large amounts
of air to disperse the propane and reduce the concentration below the LEL.
Dave
P.S. Perhaps I should be consistant and say either "petrol vapour" or
"gasoline vapor."
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