USE TANKERS OR RELAY PUMP?
APPARATUS EQUIPMENT
A formula has been devised to help decide whether to use a pumper relay or a tanker shuttle at rural fires.
A formula has been devised to help decide whether to use a pumper relay or a tanker shuttle at rural fires.
The formula considers where the nearest water supply is located and estimates how much water in gpm can be supplied by tanker. For planning purposes, a circle can be drawn around a water source to show how far the tanker can travel and still maintain a minimum flow rate. Beyond the circle or for larger flows, relay pumping or additional tankers are usually required.
Stow, Mass., has a paid on-call fire department, but there is not town water supply in the rural area. The only hydrant system is privately owned and located in a small housing development. As a result, the water supply at fires consists of either drafting or tanking from one of several water holes around town.
An initial decision whether to drop lines, draft and relay pump or tank water must be made by the officer in charge. Due to the nature of the department, this decision may have to be made by the senior fire fighter pending an officer’s arrival, especially during weekdays when most members of the department are working out of town.
Due to the broad range of experience and knowledge among the department, we needed some guidelines with which any fire fighter who is familiar with the equipment and water sources can make basic decisions concerning water supply.
Stow s primary attack piece for structural fires is a diesel-powered, 1000-gpm, mid-ship pumper. Three 1 1/2-inch and one 2 1/2-inch preconnected lines are carried, as well as a deck gun. It is thus conceivable that the full flow capabilities of the pump may be required. Indeed, even with our low incidence of major fires, peak flows of 600 gpm have been required, although usually only for short periods of time.
Tanker operations are carried out by two gasoline-powered pieces: a 1000-gallon tanker-pumper with a 750-gpm front-mounted pump (also used as a secondary attack piece) and a 1500-gallon tanker with a 1000-gpm front-mounted pump (used strictly for water supply).
All supply lines in Stow are either 2 1/2 or 3-inch, so the decision is really based upon knowing how much water can be tanked in gpm.
The equation looks like this
F = G / 30 (D/S) + Tf + Te
where
F = flow rate (gpm)
D = distance from water to fire (miles)
S = average driving speed (mph)
C = tank capacity (gallons)
Tf = time to fill tank (minutes)
Te = time to empty tank (minutes)
Now we can estimate the flow rate by dividing the number of gallons in the tank by the number of minutes required to fill, transport, empty and return one tank of water in minutes.
Solving this for D yields
D = S (G/F) / 30 – Tf – Te
As an example we can use Stow’s 1500-gallon tanker. Using its own pump, this tanker can be filled in two minutes and emptied through a jet dump in one minute. With this truck and the town’s winding roads, 30 mph is a reasonable average speed If the fire is 1 mile from water, then the first equation gives a flow estimate of 375 gpm At 1/2 mile this becomes 429 gpm. If two tankers are used the total flow is simply the sum of the individual flow rates.
These equations are meant only as general guides. The biggest single variable is average speed Road conditions, weather and driver skill make this variable fluctuate a great deal. When reasonable numbers are used, the achievable flow rates are surprising and sobering — but do help make plans realistic.
