Unsupported vs. Supported Supply Lines

Unsupported vs. Supported Supply Lines


Gene Carlson’s Volunteers Corner

How often do we hear complaints about the water supply at a fire? Too often! The pump operator reports that the pressure is inadequate or that the supply line is collapsing because you are pumping past your supply. This can interfere with extinguishment operations at a spreading fire, curtail plans for exposure protection, and necessitate dispatching additional companies to the scene.

Unfortunately, water supply problems are often caused by the fire department and not by the water supply system. Many fire department personnel do not understand their water system. Not knowing its capabilities and limitations, firefighters run into problems when laying unsupported supply lines of 2 1/2or 3-inch hose.

If properly used, the water system is often capable of providing adequate fire flow. In fact, the fire flow test had indicated that sufficient flow was available. However, it must be remembered that the fire flow was calculated at only 20 psi. This is not a sufficient pressure on which to base the effectiveness of unsupported supply lines.

The most common mistake made by firefighters when calculating the capability for supporting supply lines is to assume that the entire static pressure is available to overcome hose friction. This is an error. As the flow increases the residual pressure drops, reducing the amount of pressure available to move water.

The only sure way to determine the pressure is to graph the fire flow test for the area by selecting the gallonage that will be used, and then finding the exact pressure that could be applied to move water. It is incorrect to simply assume that the pressure needed can be accurately determined by calculating the static less 20 psi (the figure used to compute most fire flows).

In many cases a short unsupported supply line will be satisfactory for the initial attack pumper on a small residential structure. However, as additional pumpers hook up, the residual pressure will continue to drop, limiting the flow to both pumpers. Of course, on a major fire requiring large flows, the residual pressure will drop considerably. This will seriously restrict the flow through unsupported supply lines. Under no circumstances can the total flow that is available at 20 psi be delivered by unsupported supply lines.

The single unsupported supply line actually limits both the hydrant flow and use. If a hydrant valve is not placed on an unused outlet, a second line cannot even be taken from the hydrant.

A better method is to lay dual lines rather than a single line. However, this system also has its disadvantages. The end result of laying dual lines will be only twice that of the single line. In addition, picking up the hose lines is difficult due to current manpower restrictions.

The solutions to these problems are relatively simple. You should use either a large diameter hose for the unsupported supply line, or place a pumper at the hydrant.

There are three methods of placing a pumper at the hydrant that can be developed into a standard operating procedure. The first is to make a reverse lay. However, this excludes having the attack pumper and its equipment at the fire building, which is the goal of many departments. The second method is to use a four-way hydrant valve that allows a second engine or pumper to pump the line from the hydrant. The third way is to employ tandem pumping. Tandem pumping is the use of a short relay between two pumpers. (This should not be confused with dual pumping. Dual pumping involves two pumpers that are connected on their same suction side to the same hydrant. See Volunteer’s Corner, FIRE ENGINEERING, September 1984, page 8.)

The four-way hydrant valve has been in use for many years in both the Baltimore, MD, and Los Angeles, CA, areas.

Several commercial models are available. This device allows the first engine company to lay a supply line for immediate water while the second pumper hooks up to the hydrant and pumps the initial supply line.

One option is for the second engine to lay additional lines before hooking to the hydrant and then pumping through all lines. Another option is for both the first and second engines to lay in, placing two four-way valves on the hydrant (perhaps one engine to the front and one to the rear of the building) while the third engine then hooks to the hydrant and pumps the lines.

A simple, but effective, four-way operation can be accomplished by placing a gate valve on one outlet of the hydrant and a clappered Siamese, attached to the supply line, either on the other outlet or on the ground connected to the hydrant with a short section of hose. This enables a second pumper to connect to the hydrant valve for water and pump into the unused side of the clappered Siamese, changing the supply line from unsupported to supported.

With a tandem pumping operation the first engine may lay a line or lines in, but not hook them to the hydrant. The second engine can then connect to these lines and the hydrant, and then pump the lines. Another option is for the attack pumper to proceed directly to the fire and let a second engine perform a reverse lay to the water supply.

All of these methods of laying supported supply lines will serve to increase the water supply to the fireground. Two engines working together with supported lines will be more effective than two engines each laying their own unsupported lines. Another advantage of using supported supply lines is that the operation can be accomplished without additional hose requirements.

Consider the end results, review the alternatives, and develop your standard operating procedures for supported supply lines.

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