The suburban fire service is so over tasked in the post 9-11 era that we often lose sight of our primary mission: to put the fire out. Andy Fredericks from FDNY Squad 18, and a friend of mine, used to say, “If you put the fire out, you don’t have to jump out the window.” Andy was killed on 9-11 by Muslim terrorists along with almost 3000 other Americans. The American Fire Service is not as good as we should be in delivering decisive amounts of water quickly on the fireground. Almost universally, career, volunteer, combination, urban, suburban and rural departments don’t understand the critical points of water delivery on the fireground. Let’s look at a few of these points, but first a real life example.
Recently I tested the fire attack system of a very busy suburban department. They rolled in with a 1750 gpm pumper, 4” supply line and were very proud to tell me they use 2” hose and flow 210 gpm from their first interior attack line. With a good hydrant supplying water thru the 4” to the 1750 pump, thru the 2” line and nozzle we measured a flow of 120 gpm. Something in the fire attack system was not correct. The flow meter was right, we calibrated it before the test.
Fire Attack System
The fire attack system consists of hardware and software between and including the intake on your engine to the tip of your nozzle. The fire attack system also includes the critical software of the pump operator and the nozzleman. Parts of the fire attack system include: the intake valve on the pump, the pump, the discharge valve and piping, gages and pressure sensors, flow meters, the hose and of course the nozzle.
Target flow (TF) is the cornerstone of this discussion. Want to have some fun? Ask this question around your fire house: what is your target flow (TF)? My what? Target flow— the amount of water you have designed your fire attack system to flow for an aggressive interior fire attack. You know — our most critical mission — to put the fire out! In other words, how much water do you want out of your first hose line? To keep this discussion manageable I will use your first 1 ¾” hose line as an example. The short answer for your 2 ½” hose is this: target flow for 2 ½” hose hand lines is 260 gpm. OK back to our first 1 ¾” line that you have designed and use for interior fire attack.
TF must be repeatable. It is the standard procedure you have established for your company or department. With TF established, you can then select required parts to your system. Let’s work backwards from the nozzle. Let’s say your department has established 180 gpm as the TF. Why 180 gpm? It is the most water flow that two firefighters (nozzle and back up) can handle and advance the line ( with the help of the door man). Also, if we shoot for 180 gpm and only reach say 150 due to kinks, elevation or other problems in the stretch you still have a decisive quantity of water to kill the fire.
Remember, you don’t want the interior fire attack to be a fair fight. You want to kill the fire as quickly as possible with significant reserve flow if you need it.
LT Christopher Flatley, FDNY a co-instructor (AKA co conspirator) of mine says this about 180 gpm flow. If you think that is too much, do you know how to make your system flow 90 gpm? Easy, flow it for 30 seconds! Remember, the goal is to put out the fire, not engage the fire in a drawn out battle. The longer the time before you kill the fire, the longer time it has to spread thru the building void spaces and the longer time it has to kill firefighters.
Choose a nozzle that will flow 180 gpm at its design pressure. If you choose a smooth bore, it will be a 15/16th tip that pressurized to 50 psi will flow an excellent fire killing stream with good reach and excellent penetration. More on this in the next column. If you choose a combination or fog nozzle, be sure it will flow your target flow. There are some really good low pressure combination nozzles out there flowing 150 gpms at 50 psi. If you want 180 gpms, make sure the nozzle will flow it! Select carefully your fog tip. The 100 psi nozzles we are used to have about a 80 lb nozzle reaction (100 psi, 180 gpm) and can be very hard on the nozzle and back up man. The solid bore has around 69 lb of nozzle reaction and is significantly easier to use and advance. Kinks are more of a problem because the line is a bit softer, making it easier to get around corners during the push inside. More next time on this as well.
We have all suffered through the theoretical friction loss calculations at one point or other in our careers. There is a key word here — theoretical! Understanding the theory of friction loss is excellent knowledge and certainly what we need to become proficient in our jobs as engine men, officers or pump operators. However we operate in the real world with real hose, not theoretical hose.
Real hose has variations that cause friction loss and water flow to vary widely and wildly. For simplicity we say 1 ¾” hose is 1 ¾” hose. The reality is that hoses vary by brand, age, use and abuse. Some stretch a bit more making the friction loss a lot less allowing more water to flow. Some hose has rough linings making more resistance to the water flow, reducing your target flow. Older hose may have permanent creases in it where it was folded contributing to reductions in your target flow. The bottom line is this, the specific hose you have in your system may drastically impact your ability to achieve your target flow.
Mac McGarry from Elkhart Brass has done a significant amount of testing and evaluating fire attack systems and has found huge variations in friction loss resulting in equally huge variation in target flow in various brands of new 1 ¾” hose.
Things That Effect It
We have already seen how important it is to select the proper nozzle and hose let’s take a look at some other factors that impact your ability to flow decisive amounts of water.
Got a bumper or trash line on the front end of your rig? Sure, many of us do and it is really convenient — and it gets used a lot! Trace the piping back from the bumper to the pump and you will find a lot of 90 degree and 45 degree elbows and more than a couple of feet of piping. There is lots of friction loss to impede flow in the bends and piping.
More important, where is the pressure sensor located on that piping? It is probably near the pump. So, all that loss in the piping is not being accounted for by the pump operator. Most likely you are under pumping your fire attack system you use most.
How To Test It
With all these variables what is a fire department to do? Simple, flow test your fire attack system. It is the only way to reliably determine what your first line is flowing. I keep referring to the first line— just repeat the process for all your attack lines.
Here is how I do it. Since water is incompressible I put a flow meter on the intake side of the engine. I put a spring loaded flow meter on the nozzle and a pressure gauge as well as a confirmation of flow meter readings. This contraption is just for testing, not for going to fires. The members establish a water supply and stretch their first attack line. I tell the pump operator to charge the line to whatever pressure he would at a fire. We then see what the gages are telling us. About 25 percent of the time the department is close to what they wanted for their target flow. The other 75 percent of the time they are discharging somewhere between 30 and 70 gpms less than they think they are.
Other tests may find a glitch in the system somewhere else. In the example listed above, the discharge valve was not opening all the way, thus limiting the flow of water to their attack system. With that fixed their system did flow what they aimed for. But, and this is a big but, they did not know it until they tested their fire attack system.
Our Most Critical Play
Delivering decisive amounts of water to the fire quickly is our most critical play. Putting out the fire reduces all other (well most) hazards on the fireground. Establishing, testing and training your members to achieve your target flow is our most critical play. We must understand it, train to it as our standard, and be able to execute it each and every time we arrive at the working fire. It is our job and there is no excuse for not doing it right. Firefighters lives depend on it. We have the best protective gear, scba and engines available on the planet. We must be sure we have designed and can use it to get the best result.