What is the best material used to extinguish fires?
What is the best material available to man to use in fire protection systems? Oxidane, Hydrogen oxide, Dihydrogen monoxide, Hydrogen Hydroxide, Hydroxylic acid, Hydroxic acid H2O or just plain old WATER? Actually all the items listed are just water!
We are in the business of putting water on fires. Either as a fire sprinkler contractor or fire fighter. We both employ specialized equipment whose only purpose is to get water on the fire in many different ways.
What makes water such a great fire fighting medium? Both as liquid water and as vaporized steam, water has properties that make it good for firefighting. Water has a high capacity for holding heat. Thus when applied to a fire, water carries the heat away and reduces the fuel’s temperature. When water absorbs enough heat it turns to steam which is effective in displacing oxygen and starving the fire.
Because water has what’s called a high specific heat capacity, it removes heat more effectively. Kilogram per kilogram (or pound per pound), water can hold more heat than almost any other everyday substance. It takes one BTU (British Thermal Unit) to raise one cubic foot of water one degree Farenheight. Thus each cubic foot of water coming out of the hydrant at about 60°F will take 152 BTU’s to reach 212°F.
But to change water from liquid at 212°F to a steam at 212°F it requires a whopping 970 BTU’s! Thus our cubic foot of water absorbs 1122 BTU’s of heat.
So let’s look at that in terms of the water we put on fires
A standard ½” fire sprinkler will have a minimum discharge of 14.8 GPM. That converts to 1.97 Cubic Feet per Minute. Thus a standard sprinkler absorbs 2,219.8 BTU’s per minute
A standard 2½” hose steam is 250 GPM. That converts to 33.4 Cubic Feet per Minute. Thus a standard hose steam absorbs 27,497.4 BTU’s per minute
As a comparison of how many BTU’s we get from fuel I chose oak as firewood. A chord of oak will produce about 25 million BTUs. A chord weights approximately 3757 pounds. That’s about 6654 BTU’s per pound of oak.
Under perfect conditions, if we got all that energy out of the cord of oak, a 2½ hose stream would absorb all the energy in about15 minutes.
So as we see water absorbs a lot of heat energy. But what about its ability to displace oxygen as steam? When water vaporizes at 212°F it expands to a volume 1700 times greater than liquid water. At 1000°F the expansion is over 4000 times greater. So our single cubic foot of water becomes 1700 cubic feet of steam. Even in an open area this amount steam being generated would quickly displaced the oxygen.
Lets look at that cubic foot of water some more and break it down
At 52.72°F a cubit foot of water weights 62.4 pounds. A cubic foot had 1728 cubic inches so each cubic inch of water weights 0.0361 pounds. Stack up 12 of them and the column weighs 0.433 pounds. Since it has a base of one square inch, that’s where the number we use every day to calculate the pressure of a column of water
Something to think about the next time your holding the hose nozzle or calculating the discharge of a sprinkler system.