The fire had been burning for about an hour before headquarters received an automatic alarm for smoke in a store two buildings away from the fire building. The two first-arriving engine companies quickly located the source of the fire in the basement of a furniture store. So far, so good...
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Big Fires Requirw Big Water, Immediately
It's a matter of physics that combustion of solid matter causes a release of heat energy that is proportionate to the amount of material and the type of material involved in fire. To stop this energy release that is, to put the fire out the most common method used by departments for manual fire suppression is to cool the burning material to a point where it stops distilling flammable gases. This, of course, is normally accomplished with water. A given amount of solid material will produce a certain amount of heat energy and if the stream of water applied by firefighters is not of sufficient quantity to cool the amount of material involved in fire, it will not be extinguished. Simply put, it's the quantity of water applied to the burning material that will dictate whether extinguishment will be achieved.
How much water is needed for a given amount of fire? This can be calculated by using the National Fire Academy (NFA) rate of flow, rule of thumb formula that states that an involved area's square footage (length x width) divided by three approximates the amount of water that must be flowed to extinguish a fire in that area.
Photo by David P. Fornell
Where do priorities lie? In the engine above, working lines are replaced by cribbing. This engine carries only 200 feet of large handline.
Photo by David P. Fornell
The hosebed shown above contains a 2 1/2-inch 200-foot pre-connect, at left, and 600 feet of 2 1/2-inch line in the next bed for long stretches. Both lines have 325-gpm nozzles. At right is 300 feet of two-inch line with a 250-gpm nozzle.
For example, if the auto parts store mentioned at the beginning of this article measured 35 feet wide by 50 feet deep, 1,750 square feet would be involved. This number divided by three gives us a needed flow of 583 gpm. If the two first-arriving engines put two 1 3/4-inch handlines in service at an average flow rate of 125 gpm, the initial flow rate would be 250 gpm, less than half the needed gallonage. Each unit would be out of water in four minutes and the fire would not be extinguished, as was the actual case.
If we move away from the room and contents syndrome and assume that each engine was equipped with a 21/2-inch handline with an 11/4-inch tip, they could have supplied a combined flow rate of 600 gpm, or more than enough to extinguish the fire with tank water provided; the streams could hit all parts of the involved area.
Big fires require big water for extinguishment. It's a matter of physics and it cannot be changed. If a small line is pulled on a big fire and the flow rate is not sufficient, the fire will not be extinguished. It's that simple and, unfortunately, is proven every day.
Why Don't We Use Big Lines Anymore?
There are a number of reasons. The first may be that a department listened to a sales representative who oversold 1 3/4-inch hose and a nozzle that "can flow from 50 to 300 gpm." If a department believes it is flowing over 140 gpm from its 1 3/4-inch pre-connects using common combination nozzles, yet is still able to move them offensively into a fire building, it may want to borrow a flow meter for a "reality check."
Photo by Jim Regan
It's bad enough when the first-arriving company stretches a line that cannot contain the fire but that error can be devastating when the officers of the second- and third-due units continue to operate with a dwelling-fire mindset. Training, hardware research and standard operating procedures can cure this problem but the motivation must come from the top.
A good example of this mindset beset one midwestern department that purchased a new pumper with the engine at the rear. Because the rear hosebed was so high, members decided to put their working handlines over the pump in four crosslay beds. The sales rep told them they could flow 250 gpm from each of the beds using 13/4-inch hose and automatic nozzles. He was telling the truth because in theory the system he sold could flow 250 gpm but the pump pressure needed to flow that amount was found out later to be almost 300 psi. During a class in which the instructor used a calibrated flow meter, the members were shocked to find out they were flowing only 80 gpm per line rather than the 250 gpm they were promised.