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The latent heat of vaporization is the amount of heat absorbed as a substance passes from liquid to a gas. In other words, this is the amount of heat it takes to make a liquid begin to give off vapors.
In terms of fire protection and sprinkler systems, once water is applied to a fire it begins to absorb the heat being generated. Fire protection sprinkler systems are not exact. As some of the discharge is applied directly to the fire, steam will form — this water has reached the point of latent heat and is transformed to steam. Obviously, not all of the discharge from a sprinkler system absorbs heat perfectly, so there will be times when very little amounts of water are turned to steam. Steam is probably the best suppression agent out there, but it has drawbacks. First of all, it is inherently dangerous. Steam will injure or kill people in the area of the live steam discharge. Thus, putting live steam on a fire is not often done. To transform water into steam requires significant pressure depending on the temperature of the steam. But, as heat is absorbed by surfaces, the passage of water to steam increases the volume of the surface area of a given volume of water by about 1,700 times. This increased surface area means that there is much more heat absorption capability in steam, versus a flowing stream of water or droplets of water.
© Hughes Associates,Inc. 2012