Look, the situation is really simple. There is a limited air/fuel ratio
where combustion will occur. This is between about 7 and 22% by volume
(vapor to air etc) for normal car fuel. Of course nobody *alive* can
disprove this. If you do WHATEVER to upset this ratio it will not burn,
period. Or so the books say. It is irrelevant if you remove the air
(oxygen) or add fuel (vapor). Of course if there is ANY amount of hydrogen
or other low octane fuel in the mixture then you have a problem. Hydrogen
forms explosive mixures with air from about 2% to 70% by volume.  These
figures are from my single still working neuron, for normal conditions.
CHECK the numbers for any serious use. The correct explanation has to do
with flame speed, energy transfer capacity, specific heat, minimum
temperature for self-sustaining burn reactions etc etc etc.

OTOH it is (and has been ?) standard practice on tanker ships to run
exhaust through the fuel holds to keep any ignitable atmosphere conditions
at bay.

The trick with the acetylene filled coffee can is age-old. You make a hole
in the top and bottom lids of an empty tin coffee can. You put in a chunk
of carbide. You put in 1/2 cup of H2O. You put on the pierced lid. You
light the gas at the top hole (through the lid). You run. After some time
there is a boom. You use this at your own risk. Just in case you think of
suing me, this is from an English 'little chemist' experiments book I
bought second hand. I dates from about 1938 or so. Good luck *grin*.

Peter

PS: *REAL* experimenters have all their limbs attached in natural ways and
show no severe burn signs on their bodies <g>

On Wed, 26 Jun 2002, Benjamin Bromilow wrote:

>>FYI I used to have fun by lighting spent canisters for the camping stove
>>at the mouth. The canisters were totally dry inside. When lit at the mouth
>>they would burn with a small popping flame for up to an hour.
>>
>>Peter
>
>Then again, my uncle used to go round the world demonstrating the powers
>of methane for a gas company- I kid ye not.... strange the jobs some
>people have. His party piece was to fill a treacle/syrup tin with a
>push-on lid full of methane, pierce the top, light the gas and run. It
>certainly woke people up when the tin exploded (methanology is not that
>exciting otherwise). B ps Does anyone else think that welding a full fuel
>tank of petrol is slightly less dangerous than an almost empty (ie 50/50
>air/fuel mix)..... NOT THAT I AM SUGGESTING ANYONE TRY THIS!!! I'm just
>interested in the probabilities/theory. I'd feel uneasy filling the tank
>with exhaust fumes before welding. I've been near too many cars where you
>can smell the unburnt petrol. CO2 or no CO2, I'd be uneasy about doing
>any welding near that.....

<g> comes from being an MD trained in 1st aid I guess. All the rest of us
think about this in *recovery* I guess. <g>

Peter

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