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Q & A: water and fires

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Most recent answer: 03/04/2020
Q:
I am a firefighter, and have always been under the impression that in fires when we apply water it boils and converts to steam. This conversion happens with an expansion rate of 1700:1, and that at temperatures higher than 212 degrees, (most fires that we fight) this expansion rate is exponentially higher. Recently I was told this is only somewhat true and that after water expands into steam it actually condenses back down into a liquid. How is this possible if temperatures are still extremely high?
- zachary cordisco (age 28)
Fairfax
A:

The steam won't condense back to liquid until it gets far away from the fire to someplace cool. 

One detail: the amount of expansion doesn't go exponentially with temperature. After the huge expansion in converting the liquid to gas, the remaning expansion is only linear in abolute temperature. So heating from the boiling point (212°F) to say ~900°F only doubles the volume. (0°F is 460° on that absolute scale.)

Mike W.


(published on 03/04/2020)

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