>No, if there were too little (but there was enough oxygen and heat) it
>would flash off. Too little fuel is never a reason for something not
>to ignite, though it may prevent sustained burning.
Um, yeah, I believe that is what I said on the very first reply of mine.
It wouldn't catch fire, or not for more than a fraction of a second. The
concern on the original poster was clearly, would the oil catch fire and
cause a problem. My response was, no, chances are there is too little
fuel to create a sustained chemical reaction (ie: start a fire).
Flashing off, won't cause a fire. Chances are, you won't even notice it
did it (other than possibly smell the by products). And depending on the
amount of oil, and what exactly the oil is made of, it may never get the
chance to even flash off... it may "smoke off" instead. As the heat of
the fuser raises to the flash point, the oil becomes unstable and starts
to break down and oxidize. You wind up with smoke (incomplete
combustion), and all potential fuel may in fact oxidize before flashing,
leaving nothing to ultimately flash. (hence the idea, too little fuel, no
fire).
>Three things: chemical reaction is implicit in fuel+oxygen (and
>activation energy). Unless you get into esoteric things like
>substances that interfere with the reaction (like some CFCs can),
>because they change the activation energy.
No, it is four things. It USED to be considered three things... then fire
science got smarter, and realized that chemical reactions, although
implied in the oxidation process, are a VERY important process of the
fire. And attacking it is more common then people thought.
In fact, most normal people that fight a fire are probably in fact
attacking the chemical reaction. Dry Chemical extinguishers don't
actually smother a fire like many people assume, they inhibit
oxidation... ie: they break the chemical reaction. At least here in the
USA, Dry Chemical extinguishers are the most popular form of fire
extinguisher found in homes and offices (standard ABC are Dry Chem in the
USA).
Normal "civilian" ways of combating a kitchen fire:
Spray it with water: removes heat
Dry Chemical "ABC" extinguisher: stops chemical reaction
Towel over the fire: removes oxygen
Turn off the gas on the stove: removes fuel
>I know quite a bit about this actually, because my dad owned a fire
>extinguisher company.
Ahh... ok, had I known that, I might have been more specific in my use of
terms and explanations. I figured I was trying to make this a little more
"layman's". I myself have been a fire fighter for 13 years... so I hope I
know something about the nature of fire (if not, I've wasted an awful lot
of time in classes, and been darn lucky with all the fires I've gone up
against).
>The reason you use foam to combat a liquid fire
>is to smother it, because with an established fire, it's unlikely you
>can get enough water to cool it fast enough, without spreading the
>burning liquid around.
Exactly. (Sorry, I didn't explain the reason behind it, because I didn't
realize I was talking to someone that cared).
>The petrol in bucket of water trick works
>because the petrol layer is very thin and the water prevents it getting
>hot enough before the match goes out.
Except you forget about vaporization. Gasoline (petrol) vaporizes readily
at standard atmospheric pressure. If you wait for too long before tossing
that match into the bucket, you won't be igniting the fuel on the water,
you will be igniting the fuel vapors hovering over the water. The water
won't stop the heat of the match if the match is still 4 inches above the
surface. The vapors ignite... and you get a nice POP and flash as they
expand out of the top of the bucket. I wouldn't want to be standing over
it when that happens.
Depending on how much petrol you use, this could be fun to do... like I
said... you do it, I'll video tape. :-)
-chris
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Received on Wed Apr 14 2004 - 14:34:30 BST