Rate-of-flow formulas for larger fires
Standard first alarm response to a house fire for any fire department should be a minimum of two pumpers plus a support truck, that maybe either a ladder, squad, or service truck. Present day pumpers carry a lot of equipment. This includes at least four air packs and spare bottles, a generator, a ventilation fan, a 24 foot extension ladder and a 12 foot roof ladder, assorted tools, flood lights, a variety of nozzles, at least 600 feet of attack hose (1.5 or 1.75 inch), plus at least 1,000 feet of supply hose (3 in or larger diameter). One nozzle maybe a master (heavy) stream nozzle that is fixed and mounted on the truck and capable of flowing at least 400 gpm. A portable master stream nozzle may also be carried. A lot of this equipment is duplicated by equipment carried on the support truck. The pumper may carry 300 gallons of water (city) or more than 1,000 gallons (rural).
The pumper, of course, has a pump that is mounted on the truck and is driven by the truck’s motor. Today the pump is usually capable of pumping a volume of 1,000 gpm (or more) at 150 psi. Class A fire pumps are capable of pumping at higher pressures but at lower volumes. Not many years ago fire pumps were either 500 gpm or 750 gpm pumps. In fact, a little more than 100 years ago motorized fire trucks were just being introduced to the fire service. One hundred years prior to that steam fire engines were in use that were pulled by horses. Earlier than that in this country, bucket brigades were used, that required a lot of volunteers.
Many fire departments shortchange their support trucks with a manning of only two firefighters. How many firefighters are needed for a first alarm standard response? Warren Kimball states that standard manning for a low risk area (residential) is a minimum of four firefighters for each of two pumpers including the officer in command for a total of eight. The support company should provide at least four more. However, many fire departments (brigades) shortchange their support trucks with a manning of only two firefighters. This is substandard indeed, and restricts the support firefighters to performing only one task at a time. At least one third of the firefighters should be assigned to support operations.
So standard manning for a first alarm response to a low risk area is twelve firefighters. Kimball strongly recommends that these three trucks be housed at the same station so that they will arrive at the scene of a fire at the same time. This enables the firefighters to be organized into task forces that operate much more efficiently than individual fire companies from different stations. In addition the chief officer will arrive as the 13th firefighter on the scene usually driving his or her own vehicle. For high risk areas a minimum of three additional firefighters should be provided, or a total of 16.
What is the fire flow that can be provided by standard manning on first alarm for a low risk area? The answer is 400 to 500 gpm. In the initial fire attack, the first line should be in operation in less than 2 minutes after the fire trucks stop at the scene. Two firefighters should be assigned to the first small attack line (1.5 or 1.75 in), and two firefighters assigned to the second small line. The third line should be a bigger 2.5 inch line manned by three firefighters. The two small attack lines flow 100 gpm to 125 gpm, and the 2.5 in flows 250 at standard pressures and standard length of hose. Thus the NFF is 400 to 500 gpm for initial first alarm attack.
There are two ways that fire flows can be increased by using fewer firefighters. There are two ways that fire flows can be increased by using fewer firefighters. The first way is by using heavy (master) stream nozzles that flow at least 400 gpm. A monitor or deck gun is mounted on the pumper with a pipe leading from the pump. A portable heavy (master) nozzle is operated at a distance from the pumper and is connected to the pump by fire hose. In both cases the heavy stream can be operated by two firefighters. The second way is by using an aerial ladder to apply water to multistory buildings. The ladder is attached to a fire truck and the nozzle is attached to the tip of the ladder. Again this heavy stream can be operated by two firefighters. Much more water can be flowed with heavy streams, 400 gpm each compared to 250 gpm or less for each hand line.
