Potential Water Supply Limited in Inline Pumping
The Volunteers Corner
The fact that the most fires can be extinguished with a l 1/2-inch or smaller line can lead to a problem on all-hands fires. Many departments use an inline pumping evolution that has the virtue of getting a line in action quickly with an uninterrupted supply of water.
In inline pumping, the first-in engine company drops a man and a supply line at the nearest hydrant approaching the fire and the engine proceeds to the fire. Water from the booster tank is used to feed the pump and charge the first line, or lines, off the engine. These, of course, should be preconnected. Before the tank is in danger of being emptied, the hydrant man has connected the supply line and the pump operator has coupled the other end of the line to a gated pump inlet. With the opening of the hydrant, the pump now has a continuous supply of water.
But what happens when the fire requires upwards of 500 gpm or more for extinguishment? This is the moment of truth that faces the officer of the first-in engine company. Within seconds, he must decide whether the fire is small enough for the quick attack with inline pumping or whether the fire is large enough to require more water than inline pumping can provide.
Limiting hydrant potential: If the officer decides on inline pumping, then he automatically limits the potential hydrant flow. If he drops parallel lines at the hydrant or drops a single line and gates the other 2 1/2-inch hydrant outlet for a second feeder line to be stretched later, the potential flow will be greater than if only a single feeder line is stretched from an ungated hydrant. Some fire departments overcome this flow restriction problem by using a four-way hydrant valve that attaches to the steamer outlet.
Further limitation is placed on flow as the length of the feeder line, or lines, increases. A general rule that can be verified by testing is that the percentage of flow loss is not too large up to four lengths of hose. After four lengths, the flow loss percentage begins to rise quite rapidly. The moral is, keep your feeder lines as short as possible.
In a series of tests I made using the same hydrant, a 100-foot, 2 1/2-inch feeder line provided 351 gpm, but a 200-foot, 2 1/2-inch line supplied only 269 gpm. This was 82 gpm lessenough for a 75-gpm 1 1/2-inch line. When a 100-foot, 3-inch line was used, it flowed 411 gpm, but extending this line to 200 feet cut the supply to 365 gpm, or 46 gpm less. Using parallel lines, one 2½-inch and the other 3inch, 100 feet flowed 604 gpm and 200 feet flowed 558, 46 gpm less.. These figures are applicable with certainty only to this hydrant as more than the static pressure of the hydrant is involved.
Only one to a fire: From these tests and the application of the rules of friction losses in hose lines, it is evident that flow volume decreases as the length of a supply line increases. Therefore, it follows that no more than one engine company—the firstin—should engage in inline pumping. If the fire is small enough to make a quick attack advisable, two possibilities exist. The quick attack with inline pumping will extinguish the fire, or the quick attack will not extinguish the fire but will buy time for the laying of larger lines while protecting an exposure or confining the fire.
It is a mistake for a second engine company to turn to inline pumping because the fact that a second pumper is operating is an indication that the fire is probably beyond the capability of one company to extinguish. And when a fire cannot be extinguished by one engine company, then we should prepare for the use of large volumes of water. A large volume of water may not actually be needed, but second-in and later engine companies should be ready to pump at this full capacities by hooking up directly to hydrants (or at draft) with large suction.
Engine company officers have to be constantly alert for indications of the big fire when they roll in to the fireground and be ready to stretch big lines and position their pumpers at hydrants—or drafting spots. In addition to assuring the maximum water supply, this also keeps hose lines shorter because a third engine can stretch from one of the engines already at a hydrant. This third engine, in a three-engine response, can then hook up to a third hydrant to take lines from a possible second alarm company.