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Extinguishing Fire in Wind
Name: Bon
Status: student
Grade: 9-12
Country: India
Date: N/A
Question:
How does fire get extinguished with the presence of wind?
Replies:
Bon -
A fire requires three things - fuel, oxygen, and heat. Heat... means the
heat of ignition which varies from material to material. Once ignition is
obtained the chemical process (oxidation) produces heat. If that heat is
sufficient, oxidation continues from molecule to molecule and you have a
fire - combustion.
If you remove any of the three required things the fire will stop... the
oxidation will not continue. You can take away the fuel. This is how they
stop a forest fire by cutting a firebreak. You can take away the oxygen.
This is why a fire blanket works. Or you can take away the heat. One way
this is accomplished is by blowing a match out... or as you say, the
presence of wind. A surplus of air moving across the combusting surface
will remove enough heat that the fire will go out... the oxidation will
cease.
Larry Krengel
The answer depends on many factors, such as the size of the fire and
its surroundings. It sounds like you might mean an out-of-control
forest fire. If so, the key is remove the fuel (such as dry brush,
other trees, etc.) that is feeding the fire. Firefighters might dig
trenches or back-burn (create a controlled fire that burns toward the
out-of-control fire, consuming fuel in its path), or they might use
fire-retardant chemicals (or just plain water) to slow or stop the
fire.
Hope this helps,
Burr Zimmerman
Bon,
This is a great question, one that is related to blowing out candles
on a cake, where the answer is all too often said to be to do with
carbon dioxide in the breath - but we all know that a door slamming
will also blow out a candle.
I bet you remember the "fire triangle", the three things that are
needed for a fire: air, fuel and heat.
In this case you are removing the heat. Look at a simple candle
flame. The reaction between the wax and the oxygen in the air occurs
and you get a hot flame. The presence of this flame on the wick
maintains a heat source in the same location as the fuel and the
air. As the wind blows the flame it is distorted and the heat source
is stretched away from the wick, where the fuel is. When the flame
becomes separated from the wick the candle goes out.
The same ideas can be used for wind on any fire.
Normally, a certain amount of wind will actually increase the rate
of combustion and this is because fresh oxygen is being added to the
reaction at a greater rate than the natural convection currents,
this speeds up the reaction. Think of "fanning the flames" or
opening up the holes on a wood burner or barbecue. However, the wind
will remove hot gases and therefore cool the fire so there is always
a balance between the removal of heat and the adding of more oxygen.
A fire is a complex set of processes but small fires that experience
a large enough influx of air (a strong draft) should always, in
theory, be extinguished by heat removal.
Best wishes,
Tom Collins
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Update: June 2012
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