HOW EFFICIENT IS YOUR HOSE?
WATER SUPPLY
Having the right size hose can make a difference, not just in terms of getting the maximum amount of water to the fire, but in terms of cost and time efficiency. Large-diameter hose could be an answer.
One of the most common failures at an incident is selecting a hose that is too small to meet the fire needs.
Fire apparatus production statistics tell us that since 1970 fire departments are buying more 1250-gpm and 1500-gpm pumpers than ever before. Yet, a majority of fire departments in the United States hamstring their apparatus by using the two lowest priced hose sizes (2 1/2 and 3-inch), giving the lowest water flow for their custom pumpers.
We cannot continue to ignore the physical laws that govern our operations. Fire department administrators need instant results that will stop fire escalation, and large-diameter hose is a step in the right direction.
Most fire service administrators have an idea of what large-diameter hose will do, but for some reason they are not putting it to use.
To determine what size supply line to carry, it is essential to understand hydrant pressures in your response areas, hose lay lengths, manning levels, pump sizes, hose bed capacity, and vehicle flexibility.
There are a number of opinions as to the most effective means of water supply. The most recent philosophy is to forward lay one large supply line that will supply your unit to capacity. Another school of thought says to lay as many small lines as the fire appears to require Other common practices advocate laying one or two small lines and the next-in unit will pump them if needed.
With all of these methods being forward lays, there are just as many possibilities with reverse lays.
Which lay should you use? If you want your pumper supplied to capacity, research proves that a single, large (greater than 3inch), forward lay line is the most cost-effective answer. Forward lays allow the pumper to be at the fire scene and not at the water source; attack lines are shorter, allowing tower engine pressures; and forward lays allow a total preconnect operation in most departments. Smaller diameter (1 3/4 and 2-inch) attack lines with higher flow nozzles make fire attack easier and quicker. Large-caliber streams can be brought into play immediately.
Flowever, forward lays also have their disadvantages. There is a slight delay stopping at the hydrant, and forward lays normally don’t make full use of hydrant potential. If a single 2 1/2 -inch hose is laid, you can expect to make very little use of the hydrant potential. In fact, research has shown that on hydrants with discharge pressures from 10 to 80 psi, friction loss in the first 100 feet of hose will reduce flow 328 to 849 gpm. The second 100 feet will reduce flow 393 to 1029 gpm, and the third 100 feet will reduce flow 423 to 1114 gpm. A 500-foot lay can lose as much as 448 to 1194 gpm in discharge flow.
When you consider that the limit in these research tests was 528 to 1454 gpm at the hydrant, it’s obvious that your hose is a real deficit, resulting in a 62 to 84 percent loss in flow.
With a large-diameter hose, however, a single 4-inch line would experience only a 20 to 24 percent (348 gpm) loss, a 5-inch hose would bring the entire 1454 gpm to your pumper. Why mandate large water mains and use small hose?
Comparing costs and flow rates with both small and large-diameter hose. Chart A shows that a 2 1/2-inch hose is the lowest priced, and two 5-inch hoses are the highest priced. Flowever, as indicated in the flow potential column, two 5-inch hoses give the best flow potential and one 2 1/2inch hose offers the least flow potential. Chart A’s columns under price per gallon tell the real story. Based on 100 feet of hose and 10-psi friction loss, a 5-inch hose has the lowest price per gallon moved, while a 2 1/2-inch hose is the most expensive and least effective. A single 5-inch hose of modem construction can move as much as eight times the water that a single 2 1/2-inch hose will move at the same pressure.
It should be noted that not just the size, but the type of hose affects flow as well. In actual use, some synthetic rubber in the 2 1/2 to 3-inch range will flow 27 to 29 percent more at the same friction loss as standard doublejacketed fire hose. A reduction in friction loss as much as 42 to 66 percent is possible with any type of hose.
As shown in Chart B, which is based on a 1250-gpm pumper, a 50-psi hydrant pressure, and a 300-foot forward hose lay, any hose smaller than 4 1/2 inches will not supply your pumper to capacity.
When we talk multiple 2 1/2 or 3-inch supply lines for pumpers in the 1250 to 1500-gpm range, we’re talking excess cost and inefficiency. What would six 2 1/2 -inch lines cost you? Based on a 300-foot lay, you would need 1800 feet of hose that would pay out six at a time, a six-port hydrant, six 2 1/2-inch inlets on your pumper, a great deal of hookup time, and a very confused fireground. The cost for just the six 2 1/2-inch hoses is 100 percent.
Maybe your department pumps its 2 1/2 -inch lines using a four-way valve. This requires four lines, costing 93 percent of the total price of the six 2 ⅛ -inch lines. A 3-inch hose would need four lines, costing 97 percent of the total price of the six 2 1/2-inch lines. Using a single 4 1/2-inch hose to get the full 1500 gpm would cost 52 percent of the six 2 1/2-inch lines, and a single 5-inch line would cost 67 percent. “
Forward laying one line that will handle fires up to the pumper’s capacity seems the most logical and simple decision. Will a 1500-gpm supply line work on a 10-gpm trash fire? I think so. But will the supply line for a small fire supply the big, spreading fire? It will if you’re using large-diameter supply hose that fits your pump size, water supply and expected hose lay length.
The complaint is often heard that “We don’t have the water to supply large-diameter hose.” And over and over again, buildings burn to the ground. In response to this lament, the question asked is, “How long before the fire did you know that and what have you done to address it?
At the fireground, large-capacity pumpers are often positioned in the forward lay mode, with one or two smalldiameter lines trying to supply the pump. If the water is there, it just never gets to the pump. Why did the manufacturers of apparatus put 4, 4 1/2, 5, or 6-inch inlets on the pumper ? Why is the auxiliary suction (gated 2 1/2 -inch) given that name ? If it was intended to be a primary suction, it would have been named that.
“Not having the water” is all the more reason to use large-diameter hose. For example, suppose the worst hydrant in your community flows 200 gpm at 10 psi. A single 2 1/2-inch line will move that 200 gpm 100 feet. A 3-inch line would move the 200 gpm 250 feet, a 4-inch line would move it 1800 feet, and a 5-inch line would move it 5250 feet. You do have the water, it s just not making it to the pump Why? Friction loss in small hose is eating up the flow. If your hose was 300 feet long, your flow would be only 100 gpm with 21/2-inch hose. With any hose larger than 3 inches, it would still be 200 gpm
Whether to use four-way valves is a cost benefit question. For example, if you intend to move water 600 feet with a 3⅛inch hose with a four-way valve, you will move 750 gpm at 200-psi pump pressure. A 1000-gpm pumper would be the minimum to supply that line unless you have a strong water system. If the 31/2-inch hose was not pumped, you can expect a flow of 465 gpm at 50-psi hydrant pressure. At 80-psi hydrant pressure, you would get 600 gpm. The four-way valve and a pumper at the hydrant give a net end result of 285 gpm or 150 gpm in this case. This is, of course, assuming no friction loss in the valve and that the valve can move 750 gpm.
Forward Lay Relay Hose Selection Guide
The cost of the four-way valve and the 3 1/2-inch hose is equivalent to the cost of a 4-inch hose. A single 4-inch hose in a forward lay with a 50-psi hydrant will move 750 gpm; with an 80-psi hydrant, 1000 gpm. If the single 4-inch line was pumped, you could expect 1500 gpm.
Just simple dollar and cents sense tells us hose is much cheaper than a pumper. So why in the fire service, in the name of efficiency, do we lay a line and hope someone else will load that line with their pumper ? If two 1000-gpm pumpers are needed to move 1000 gpm, can we call that efficient? Wouldn’t it be better to carry the hose that will supply the entire 2000 gpm?
To determine what size large-diameter hose is best for your department, first determine the average hydrant pressure in your area. For example, some larger departments may find it more efficient to have large hose for the business districts and smaller hose for the residential areas, depending on the flow they wish to generate. Second, determine what size pump you are trying to supply, and third, determine the average hose lay your companies are making. These three steps provide all the data you need. Local conditions may require carrying more hose than the average hydrant spacing or average lay. The final decision you need to make is whether to lay one line or two lines and whether a forward or reverse lay is going to be used.
Reverse Lays Relay Hose Selection Guide
Reverse Lays Relay Hose Selection Guide
Once you’ve made these decisions, Charts C, D, E and F will help you choose the correct minimum size hose. To use the charts, simply line up pump size with hose lay length under the appropriate pumper or hydrant pressure. For example, to estimate the size hose to use for a 1000-gpm pumper, a 300-foot forward hose lay, one line, and a hydrant pressure of 25 psi, use Chart C. The correct minimum size hose to use is 41/2 inches. If two lines were laid and all other conditions stayed the same, Chart D would be used and two 4-inch lines is the answer. If a reverse lay is desired and all conditions stayed the same, a single 3 1/2 -inch hose could be used at pump pressures of 150, 200, or 250 psi; if two reverse lines are chosen, a 3-inch and a 2 1/8-inch will work at 150 psi or two 2 1/2-inch lines at 200 or 250 psi.
Plan possible fire areas to determine what your largest lays and normal lays will be. To help you decide cost benefit, each chart has underlined the least expensive hose size for a given situation. If during your figuring you come up with an asterisk in the hose size column that means to go to another chart because that method of supply won’t work.
The prudent fire chief will use this resource to determine the best way of equipping new or existing apparatus. By using a complete system approach, better productivity and adequate water to reach each vehicle is guaranteed. It is a good idea to provide more water than the pump can move.
One fire chief demonstrated how his department could supply to capacity all three of its 750-gpm pumpers 600 feet from a hydrant by using a 5-inch hose instead of a 4-inch hose.
A standard fire attack in this community is for the first-in unit to catch a hydrant and attack the fire. Each subsequently arriving unit attaches a 5-inch line to either the front suction or remaining side suction and lay 50 to 200 feet of hose and take their supply from the water the first unit couldn’t use. This is known as tandem pumping. One supply line, full flow from each pumper, no spaghetti. A simple and straightforward method of operation.
It would be unfair to say large-diameter hose is just for supply. The most progressive departments supply monitors, aerial platforms, ladder pipes, relays, sprinkler systems, standpipe systems and hand lines with one line. Laying one line instead of two or three offers time efficiency, less hose, lower cost, less fireground confusion, easier cleanup, and fewer fire fighters to do a better job.
If it s your intent to go with large-diameter hose, go all the way. Improve supply and attack. The technology is here, the time is now. Invest in a better way.