Low Water Application Rate Can Mean High Loss Record
departments
The Volunteers Corner
Sometimes a line with an inadequate rate of How is used to attack a fire because of the fear of running out of tank water or causing excessive water damage. Sometimes that line is selected because it’s the one “we always use.”
Automatic sprinkler system engineers live with the fact that water density—or application rates—must be varied to fit the fire load characteristics of the materials to be protected. In other words, a sprinkler system designed for a furniture factory must be able to provide a higher water density (gallons per minute per square foot) than a system protecting an office occupancy. The obvious reason is the difference in the fire loads of the two types of occupancies.
Like the sprinkler engineer, the first-in company officer has to select a water application system (hose and nozzle) that will hopefully provide an application rate that is sufficient to darken down the fire. We say “hopefully” because there are some fires that are beyond the capabilities of a fire department and its water supply.
The Btu problem: Basically, the successful application of water to extinguish a fire follows a very simple law: The water applied to the fire must absorb more British thermal units (Btu) than the fire is producing.
If the water application rate is not high enough, the fire will continue to burn and even increase in magnitude under condit ions favorable to maximum burning. At this point, water damage will be the last thing you may think of, but the property owner may later wonder why the fire was allowed to consume such a vast amount of combustible material. At that point, it may be somewhat difficult to explain that “we didn’t want to do any water damage” or “we didn’t want to run out of water.”
To strike an optimistic note, you will eventually extinguish the fire—when it burns down to the capability of your hose stream or water application rate.
Big fire, big stream: The objective of the first-in company officer should be to evaluate the volume of water and make his first attack stream the size he will eventually use. If the amount of fire requires it, the first stream might have to be a 500 or 1000-gpm master stream rather than a 100 or 250-gpm hand line. In many cases, all that is needed to darken down the fire is a 50-gpm line. What the fire officer must remember is that he has options and he must choose the option that best meets the requirements of the volume of fire.
Admittedly, it is easier to order the initial use of a 500-gpm stream when you have a hydrant system guaranteeing a continuing water supply than when there is no water main and the only water you have until the next piece arrives is the 1000 gallons in the tank of your attack pumper. This latter situation is where your judgment and confidence in your judgment make the difference between a good stop and an excessive loss.
You have to recognize those situations where a 500-gpm blast will darken down a fire in a minute or less, but a 125-gpm stream will have no fire-killing power. What about water damage with the 500-gpm stream? There won’t be any water damage worth mentioning if you shut down that stream the moment you darken down the fire.
To turn to the (lip side of the record, you also have to recognize conditions when a master stream, no matter how quickly shut down, would cause excessive water damage. This also is true of 250 and 300-gpm hand lines, but a good nozzleman who is quick to shut down can save the situation from being a total washout of a room.
Saving limited water supply: In rural and suburban areas where all water arrives on the fireground on pumpers and tankers, the fear of running out of water can lead to unfortunate decisions. If you have a steel drum with burning paper, you could extinguish the fire with a gallon of water properly cast over the burning surface, but the fire would continue to burn if you “saved water” by applying the gallon ounce by ounce with a shot glass. It’s the difference in application rate again.
However, there is a vital decision you have to make when your water supply is limited. You have to decide whether the water on hand is sufficient to darken down the fire if applied at the proper rate—with some water left for overhaul—or whether your water supply is so limited that using it to protect exposures will result in saving the largest amount of property After all, there is always the possibility that you could put all your water on the fire, fail to knock it down, and lose both the fire building and the exposures.
There is a time element in making a decision on what to do with a tank of water on the initial attack pumper. How long will it take for the second apparatus carrying water to reach the fireground? The answer to this question will determine whether you can expend all the water on the first-in pumper on a heavy stream—or blitz—attack.
With a hydrant system, you have no fear of running out of water, but you still have to consider the application rate for each hose line. Unless a hose stream is knocking down fire, it is not doing its job. Evaluate the effect of hose streams on the fire. When there is sufficient volume of fire, two 250-gpm hand lines can be ineffective in comparison with a single 500-gpm stream.
It’s the rate of application that is important. You could fritter away 500 gpm through ten 50-gpm hose streams while the building burned to the ground.
