Wow, that's a great question. When I was in
graduate school, I got to light controlled fires
and put out controlled and wild fires. I think
fire ecology is really interesting, but this
question had not occurred to me. Here's what I
think. Fires need 3 things: fuel,oxygen, and
heat. Water can influence all three. If there's
enough water, it can smother the fire, by keeping
away oxygen. Usually,though, it absorbs heat.
When something like wood is burning, heat
causes some of the solid wood to turn into gases,
and that is what actually burns. Burning the
gases makes more heat, which causes more of the
wood to go into the gas state,and so on. That's
why fires grow exponentially. So if there's not
much heat, then you can have tons of logs but not
actually have usable fuel.
water comes in. Water has a lot of "thermal
inertia."This means that it takes a lot of energy
to raise the temperature of water. It will also
hold that heat for a long time. That's why it's
warmer by the ocean or lake in the winter and
colder by the water in the summer.
when we put water on the fire, it basically
absorbs the heat so that the fuel doesn't turn
into burnable gas. Fire burns at thousands of
degrees (depending on the fuel). Water only gets
to 100 degrees C before it boils. So there's not
much relative difference between cold and hot
water temperature compared to the huge difference
between the fire temperature and the water
So there might be a very small
decrease in the fire-fighting power of warmer
water, but I don't think that it would have a very
On the other hand, air
temperature and humidity (the amount of water
vapor in the air) have a powerful effect on fires.
When it was too hot and dry, we wouldn't set the
controlled fires because it was too risky.The
potential fuel was already closer to vaporization
and there was very little water to buffer the
increased temperature of the fire. When it was
too cold and humid, it was hard to make things
One way to increase the fire-fighting
power of water is to turn it into foam. Why do
you think this works?Thanks for asking.
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