THE VOLUNTEERS CORNER
HOW DOES the use of tankers compare with pumping water through a long relay at a rural fire? An answer was given at a recent demonstration in Connecticut. Six tankers were used to keep 250 gpm of water flowing at the fire.
Each tanker was equipped to be first due and pump all the lines used on a fire. One tanker assumed the first-due role, a second went to the water source and the others acted as nurse tankers.
A 1-mile run was simulated by keeping each tanker in a holding area for 3 1/2 minutes after being refilled. The fireground tanker had two 2 1/2-inch gated suction inlets. A length of 2 1/2-inch hose was attached to each inlet so that while one line was being used to refill the fireground tanker, another tanker could hook up to the second line and be ready to take over the refilling job.
The demonstration was supervised by Chief A. Morrison Ennis of the Mortlake Fire Company in Brooklyn, Coim. In his area of northeastern Connecticut, Chief Ennis explained, an alarm calls for response by three tankers. If necessary, the first-due officer may call for three more tankers.
Chief Ennis, who is a member of the National Fire Protection Association’s Fire Department Equipment Committee, maintains that the use of tankers supplies more water than a mile-long relay and is more dependable.
“In a relay, if one pumper breaks down, you are out of business,” Chief Ennis explained. “If a tanker breaks down, and you are using five tankers, then you have lost only 20 percent effectiveness.”
Many experiments with tankers have led Chief Ennis to expect about 2 minutes to be spent in refilling a tanker at the source, about 4 minutes used in road travel and about 2 minutes for filling the fireground tanker.
If a tanker remains at the water source (as a supply pump), much time is saved. There is no switching of hard suction hose from one truck to another and there is no jockeying to get a piece to the water source. A length or two of 2 1/2-inch hose from the source pumper allows the empty tanker to take a convenient position for refilling. Two lines may be used so the next truck can hook up while waiting.
By actually measuring the amount of water discharged by a tanker after being refilled under simulated fireground conditions, Chief Ennis has found that the best location for the tank-fill line is near the bottom of the tank. This avoids undue turbulence and entrapment of air, which can cut the amount delivered.
Also, there must be sufficient venting to permit rapid refilling. This means that there must be provision for venting 50 to 60 cubic feet of air a minute.
Refilling through the top of the tank has been tried with unsatisfactory results. First, the hose line is difficult to hold when about 400 or more gallons of water per minute are flowing.
Secondly, overflow is a problem. At any time, this means a wet hose load, and in freezing weather, it leads to icing that makes holding the hose more difficult.
Baffling is an important feature that must be built into the tanks. In any transportation of liquids, this is done, of course, to minimize surging of a heavy load. In tanker operation, baffling must also include proper openings so that the entire load may be pumped out quickly.
There must be a large enough sump to keep the pump supplied as the water flows past the baffles. Also, the pipe from the tank to the pump must be at least 2 inches, preferably 2½ inches.
In one tanker tested, it was found that a valve in the tank-drop 2 ½-inch pipe had a constricted opening that measureably slowed delivery.
A tank-fill gage is another important item, Chief Ennis emphasized. If the gage is near the suction gates, the rate of fill can be controlled on the fireground tanker so that the tank will neither overflow nor run too low on water for safety.
Three men are regarded as sufficient for operating nurse tankers efficiently. The tankers used in the demonstration had 1,000-gallon capacities—except for the fireground tanker which could hold 1,500 gallons.
This keeps the trucks small enough for most volunteers to handle without any big-truck driving experience. Also trucks of this size can operate easily on rural roads and farm lanes.
Because the fireground tanker works close to the fire, only a few hundred feet of 2½-inch hose and enough 1 1/2-inch hose for about four working lines are needed. This means that the hose beds of the tankers can be relatively shallow, compared with those on the average pumper.
The goal of putting a maximum of 250 gpm on the fire was chosen, Chief Ennis explained, because that is the volume of the standard Underwriters’ hose stream and more than can usually be obtained in a long relay.