A Case In Support Of Large Diameter Hose

A Case In Support Of Large Diameter Hose

WATER SUPPLIES

Using the proper size of large diameter hose can result in many tactical advantages for your department. However, there are some criteria you must measure prior to putting through a purchase order for large diameter hose. A few of these are: 1) determine your desired fire flow (you have to recognize all the target hazard areas in your district), 2) determine the hose lay distances that would be needed to reach these specific high hazard areas, and 3) consider your department’s specific logistics, operations, and finances, i.e., pump capacity, fireground operations, maintenance, and cost effectiveness.

Although these points may seem obvious, their relevance must not be ignored or taken too lightly. You don’t want to find yourself in the unpleasant position of explaining the capital waste of purchasing 5-inch hose when 4-inch hose would have been more than sufficient. Perhaps even worse, you don’t want to make the mistake of purchasing an above ground water main that cannot be adequately supplied with the below surface water system supply capabilities.

A relatively small increase in fire hose diameter results in a very large increase in the hose cross-sectional area. Therefore, large diameter hose allows for movement of maximum amounts of available water over long distances with minimal friction loss. For example, a 5-inch hose has almost four times the area of a 2 1/2-inch hose. With a pressure drop of 15.2 psi per 100 feet, you can move six times the quantity of water in a 5-inch hose than you can with a 2 1/2-inch hose.

Classroom mathematics have always demonstrated the reduced friction loss with the use of large diameter hose. However, the attitude may be “who cares” by the individual who pictures a 100-foot section of 5-inch hose constructed of the conventional rubber lined cotton jacketed hose. He is naturally visualizing a fire hose that is much too heavy and bulky to be of any practical use on a fire scene.

This is an inaccurate assumption. Modern fire hose fabrication techniques employ lightweight but durable synthetics, making the weight and bulk of large diameter hose more convenient to use on the fireground. In fact, I have worked with firefighters who prefer to lay and pick up a few 100-foot, 100pound sections of 5-inch hose instead of many sections of 2 1/2-inch and 3-inch lays that would be necessary to meet the required fire flow.

So, in a fire department where the “above ground main” concept is part of the standard operating procedures (SOP), a single pumper may be positioned hundreds of feet from the water source and still achieve its full pumping capacity from a single lay of large diameter hose. This above ground extension of a water main brings water closer to the fire or target hazard area without the costly burden of adding to the local water system.

This is another advantage of the hose. It frees both the relay pumper and the crew to locate to a more strategic position or keeps them available for the next alarm.

The following is a list of the advantages of the 5-inch large diameter hose, based on my own experiences and the experiences of others within the fire service:

• Frees the relay pumper to remain in service. Even though you cannot increase the available water in a hydrant, the proper use of multiple feeder lines and relay pumping does increase the availability of the water over long lays. This is possible since either of these, or the combination of the two, reduce the effect that friction loss plays on the water flow. However, the 5-inch large diameter feed enables the same flow over longer distances in a single lay without a relay pumper.

The following two situations may better illustrate this point. Diagram A (opposite) shows a multiple lay of two 3-inch lines supplying a pumper 250 feet from the hydrant. The friction loss in this 250-foot lay is approximately 28 psi. A longer lay or additional water flow on the fireground is not possible in this situation if the engineer does not want to go below the safety of a 20 psi minimum reading in his compound gage. However, an increase in the length and gallonage of this multiple lay is possible with the assistance of a second (relay pumper) to compensate for the existing 28 psi friction loss.

Diagram B is an example ot a single lay of 5-inch large diameter hose. The residual and compound pressures plus the friction loss in the feeder remain nearly identical to those in Diagram A. However, the distance between the water supply and the engine has increased from 250 feet to 900 feet. If the 900-foot lay was reduced, friction loss would drop, and the flow to the engine would increase. In this case, the capacity of the hydrant is available with only a minimal concern for loss due to friction. Thus, a relay pumper is not necessary.

• Enables more efficient use of manpower and equipment. The implementation of a 5-inch feeder frees the apparatus, equipment, and manpower that would be required to set up and operate a relay system. The men and equipment can be more effectively located and used in rescue operations, ventilation, fire control and suppression, and evacuation activities. Regardless of the condition of the engine or the size of the crew, I can’t imagine either being turned away on a fireground requiring large volumes of water.
• Forward or straight lay (laying a water supply system from the hydrant or source to the fireground). This SOP makes at least one of the early fire attack decisions simple, while providing maximum efficiency. By connecting to the hydrant with the first engine in, or to any one of the additional responding engines, you can bring a continuous water supply onto the fire scene with you. This standardization enables quicker and more effective rescue, ventilation, and fire suppression activities. It also frees the street from multiple feeder line congestion, which usually hinders the mobility and effectiveness of additional emergency apparatus.
• Forward hose lay easily changed on the fireground to a reverse hose lay. In the few circumstances when large volumes of water are required through lays that would be excessive for a 5-inch feeder, the high-pressure characteristics and sexless couplings enable quick, simple flexibility of the SOP. The hydrant connection coupling is easily removed so the feeder can be connected first to the fireground engine and then stretched to a relay pumper.
• Long life expectancy. The hose is constructed of a synthetic outer lining with modern hose fabrication techniques using polyester reinforcement and polyurethane inner lining. This seemingly space-age construction produces a hose that is resistant to the numerous chemicals with which it will come in contact on the firegrounds and street gutters.
• Quick, easy cleaning. The 5-inch large diameter hose is totally resistant to mildew and rot. Cleaning becomes practically effortless. For stubborn spots you can use a hose hooked to a warm water faucet, soap, and a kitchen broom. This is much more preferable than the usual ritual of returning to the station to face a hose washer and several sections of dirty, cotton-jacketed hose.
• Lightweight. A 100-foot section of 5-inch large diameter hose weighs about 100 pounds. This section can flow 1,200 gpm with 9.5 psi friction loss. The flow and approximate friction loss in a multiple lay of 2V2-inch and 3-inch lines of rubber line, cotton jacket requires ten 50-foot sections of an approximate combined weight of 390 pounds plus additional lifts and carries.
• On-scene reloading. When it is not very dirty, the hose can be reloaded into the bed on the fireground. This enables an engine to be available for the next incident upon leaving the previous scene. This procedure is usually preferred over handling hose a second time once you return to the station.

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• Increased water flow. The combined cross-sectional area of a 2 1/2-inch and a 3-inch hose is approximately 11.977 square inches. The cross-sectional area of a single 5-inch large diameter hose is approximately 19.635 square inches. An increase in cross-sectional area reduces friction loss and increases the available flow.
• Reduced space, maintenance, and expense of reserve hose storage. Many of the disadvantages of hose storage are eliminated when the necessity to replace wet hose is no longer a concern.
• Recognized by ISO. The Insurance Service Office (ISO) places 39% of its grading schedule on water supply. Granted, this involves a great deal more than the size of a feeder line. However, the ease with which a 5-inch large diameter hose technically places a hydrant on every fireground must be a step in the right direction when striving to improve the department’s ISO rating.
• Permits capacity performance of large volume pumpers. Granted, this point can be supported or disproved depending on the situation. However, if the hydrant has the capacity, a 1,750-gpm pumper can be used to its fullest from a single section of 5-inch hose. Of course, the length of the lay influences the results, but the same cannot even be considered with a single section of 3-inch hose, and it would be very difficult with a multiple section of 3-inch hose.
• Easily repaired if near coupling. A damaged section can be returned to service by removing four retaining bolts, removing the hose from its coupling, making an even cut behind the damaged location, replacing the newly cut edge into the coupling, and returning the four bolts. This procedure does not involve the time and difficulty of removing an expansion ring. It also does not require special equipment to reconnect hose to coupling. In this way, a section of hose that would normally have been set aside when it did not test out properly, can be quickly repaired and pass its annual test. It even makes it possible to repair hose on the fireground.
• Less expensive. At one time, a one-foot section of 5-inch large diameter hose was 20 cents less than the combined cost of an equal length of 2 1/2-inch and 3-inch rubber lined cotton-jacketed hose. I have not conducted a cost comparative analysis on hose recently, but I have been told by co-workers who have bought hose over the last 10 years that the 5-inch hose discussed in this article is the most economical approach to hose purchase.
• Ten-year unconditional warranty. For a hose that offers as much as the one that inspired this writing to come with a 10-year unconditional warranty is icing on the cake.
• The large diameter fire hose has established credibility in today’s fire service. It is undoubtedly a revolutionary piece of equipment that will continue to be found in more and more progressive fire departments every year.