"We’ve always done it this way." "We’ve always used this equipment." or "That’s what the chart shows." Does this sound familiar? It’s generally referred to as tradition. Tradition is what we do when we’ve forgotten why we do it! How do we determine if we’re caught in the dangerous trap of tradition? Ask yourself two questions, "Says Who and With What proof?" Take fire hose and fire nozzles as an example. Who says a 1¾" hose will flow 150 gpm or a maximum of 200 gpm? Will a 2½" inch hose flow 250 gpm with a maximum of 300 gpm? Do your 200 gpm nozzles ever see 200 gpm? Could your 1¾" hose possibly flow 300 gpm or your 2½" flow 500 gpm? Have you ever analyzed the articles you read regarding fire streams that calculate the flows of multiple hand lines and monitors?
If you readily accept what you read without questioning it, you may be surprised by the actual measured flows versus the traditional calculated method. The question about flow rates is are they calculated or measured? Measured flow rates are performed with a properly calibrated in-line flow meter or with a pitot gauge and a smooth bore. Flow meters are easy to use and will measure a wide range of flows with excellent accuracy if they are calibrated properly.
It’s important to be aware that there is a calculated nozzle flow and a calculated hose line flow. Calculated hose line flows are what manufacturers share with us for simplicity of pump operation. These figures come from the formulas provided by organizations such as IFSTA, NFPA and others. Measured hose flows may be quite different.
We always refer to "friction loss" when speaking about hose lines. What determines friction loss? Key factors are:
- The construction of the fire hose
- The volume of water flowing
- The length of the hose lay
Traditionally a friction loss chart is used to obtain these figures. However, are these figures accurate? To answer this question I contacted a leading hose manufacturer. The representative explained that friction loss is the inlet pressure minus the outlet pressure of a length of hose and is measured with a smooth bore nozzle at a specific pressure. According to the representative, their tests are performed with smooth bore nozzles due to the inconsistency of combination nozzles. They cautioned against using one given friction loss for all hoses of the same size because of the significant differences between brands and models. The manufacturers claim that friction loss in one brand of hose can be double that of another. If this isn’t alarming enough, consider how flow rates affect friction losses. As flow rates are increased to the upper limits of the hose’s capabilities, friction loss will more than double. A recent test measured 138 pounds of friction loss in 150 ft. of 1¾" hose flowing 275 gpm without exceeding 200 psi engine pressure. Compare this to nozzle manufacturers friction loss charts. Although they do provide us a comparison, it’s obvious we shouldn’t rely on the charts alone to calculate our flows. Why do you think the manufacturers have disclaimers at the bottom of their friction loss charts? When looking at any chart you should be aware that they come with disclaimers for a reason. You should know what that reason is, for the safety of yourself and your people.
Nozzle flows are determined by using the hydraulics formula GPM=29.7 x D squared x Ö p (GPM = gallons per minute, D = diameter, p= NP pressure), for water flowing through a circular orifice (smooth bores) and are the benchmark for all testing in regards to hose and nozzles. This formula can only be used for circular orifices, which means combination nozzle flows cannot be calculated.
Like the hose manufacturer, if you’re using a smooth bore you can measure hose line flows accurately with a pitot gauge utilizing the previously mentioned formula. What if you are using combination nozzles? Remember you cannot calculate the flow rate of a combination nozzle. If you don’t have access to a flow meter you must rely on the data provided by the manufacturer of your nozzles. This raises the questions, "Says Who?" and "With What Proof?" Remember that the hose manufacturer didn’t rely on the data provided due to inconsistencies. A recently published report of a combination nozzle user claimed a performance test of their nozzles revealed more than a 20% failure rate. So how do we determine if our combination nozzles are performing to specification? Check with the manufacturers and you may discover that you are required to perform regular service tests to ensure the nozzle is performing properly. Can a combination nozzle be service tested (performance tested), without a flow meter? How do you service test your nozzles?
Note: don’t blame the nozzle manufacturers for nozzle failure because they clearly state that you need to service test and lubricate the nozzles regularly. Some automatic nozzles have a large coil type spring internally that weakens with use; similar to the coil springs on the older model automobiles. When the spring weakens, it directly effects the flow rate. It’s suggested you contact the manufacturer of your nozzles and ask if any specific service procedures are recommended and if so, ask them how and why?
Why don’t we, as a Fire Service, require performance testing of the nozzles available for purchase? This is a question every fire fighter should ask. NFPA and OSHA for example, require testing of important equipment. ISO requires the newly delivered fire engines to flow test the pumps without accepting the manufacturer’s data. SCBA’s, elevated devices, ladders, hydrants and fire hose all require regular performance tests. Let’s assume we do proper testing to confirm nozzle flows and pressures. That’s good, but there is another dilemma some may not be aware of. Wouldn’t you agree that it’s a common practice for many departments to lower engine discharge pressure so hose lines can be managed by available manpower? Beware: this reduction in pressure may create a very serious situation! What happens to your flow rate if you drop your nozzle pressure from 100 psi down to 75 psi, which is common place on the fire ground? Referring to one nozzle manufactures flow chart, a 25% reduction in nozzle pressure reduces the flow from just over 200 gpm down to 75 gpm! How many of you believed you were delivering 200 gpm because of the type nozzle you’re using yet you may have been actually flowing 75 gpm because of depressurizing the line. This is not the fault of the manufacturers. They quite clearly print what happens when you carry out such an action. What they don’t tell you is to read the book! We must take responsibility for the proper training of our personnel and ensure they understand every aspect of their equipment to include what happens when you don’t operate it properly.
Flow test your hand lines with a calibrated flow meter and an in-line pressure gauge at the base of the nozzle. Set the engine pressures to what you normally would use. The actual flow rates may be surprising and even disappointing. I have assisted in other departments’ flow tests of their pre-connect hand lines with results showing flows below 50 gpm while they believed they were 150+ gpm.
Unfortunately, the Fire Service does not require performance testing of nozzles, nor are our firefighters properly trained and educated about the fire streams they use. If you were going grizzly bear hunting would you rush to Alaska and grab just any gun without knowing its size and capabilities and then attempt to shoot a killer grizzly? Think about it, firefighters do it everyday. Always take in a big enough gun, that you know works because you’ve tested it, as though you’re going in to face a killer… because you are! If you’re responsible for sending your people into a fire, are you confident your equipment is of sufficient size and is performing properly?
Lives could depend on it!
Reprinted with permission, see American Fire Journal, April 1997 issue
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