Don’t be Overwhelmed by the Pressure
By David E. Mohr, P.E.
About the author: Dave Mohr is a registered Fire Protection Engineer and a 20+ year veteran of the New Durham Fire Department. He also served with two other departments previously, dating back to 1959; and he is a member of three NFPA committees, including 1001, Firefighter Professional Qualifications.
You will sometimes hear an off-handed remark, which upon reflection, becomes significant. I remember a post-incident conversation when the pump operator was recalling his initial charging of the line and its effect upon the nozzle crew. "I guess they (the hose crew) weren't ready for it (the water). I applied standard pressure to the line and it almost lifted her (the nozzle person) off her feet." Laughs ensued. We can discuss in another article the importance of notifying the hose crew of when water is coming. For the present, I'd like to draw attention to fallacy using "standard pressure" when operating the pump.
The implication behind "standard pressure" is that, at least early at a scene, the operator has a pre-established pressure at which to set the pump. In this particular case, the "standard" was 150 psi. "I pulled up to the scene; hose was pulled off and I ran up the pump to show 150 psi." Let’s look at this mentality of standardizing pressures a little closer to see if it is practical. Most will agree that prearranged operations are vital to safety and effectiveness in the turmoil of the fire ground, but we must always examine the implications and consequences of such operations.
In order to have a "standard" for pressure, every element affecting the pressure has to be standard as well. Hose length, nozzle type, elevation changes, physical location of crew - on a ladder or stair well, on a ice-laden driveway, etc. - and the demands of the fire itself, all have their direct effect upon pressure selection. For example, use your imagination to construct how many different attack-line configurations are possible just within your own department. Then calculate how much water will flow when the standard 150 psi is applied to each configuration. The results range between too little and too much water. So you must somehow standardize all these other factors before you can standardize the resultant, the pressure. No matter how hard we try, even if we think only of our main attack piece, standardizing just the hose-line length is impractical. We may want to be able to grab the 150-foot cross lay as our primary attack line, but this is only practical most of the time. Safety and effectiveness have to be considered ALL of the time. What about the other pumpers in your bays; what about mutual aid responses where you hook up to lines already laid by some other department? Do you react with a "standard pressure" under these conditions? Not on my watch!
What automation can we employ to help satisfy the needs of standardization and to quell that commotion of arriving first on the scene? You can standardize on that element that reflects the dynamics of the fire ground. It is water flow that puts out fire and it is the water flow that can be standardized, to some extent and, at least, initially. Suppose we will initially flow 150 gallons per minute (gpm) when we arrive at a scene until further instructions are issued. 150 gpm will produce a predictable suppression capability. (See other articles in this series for estimating just how much suppression any given flow can produce.) By focusing on the gpm, the pump operator must first account for each of factors above. Ultimately, this is the essence of being a pump operator. Thus, the nozzle crew will know what to expect for nozzle reaction and suppression capability.
This latter expectation is not to be regarded lightly. Not much experience is needed from working a line at 150 gpm to recognize a blaze so developed that there is insufficient water to undertake an attack safely. Hence, the standardization based on gpm requirements forces the pump operator to consider particulars of the hose lay. Requiring gpm also gives the people on the other end of the hose the assurance of having a predetermined level of effectiveness to bring to bear against the fire.
Yet the crucial point remains in that using a prearranged gpm is still second best. The best situation is when the Fire Officer (FO) makes an assessment of volume of fire. Then the FO translates that into an order directly to the pump operator to supply the volume of water appropriate to that particular fire. The pump operator sets the pump’s pressure to the standard of flow ordered by the FO. Therefore, the standard should be that the FO investigates and then instigates the proper gpm. However, if the department insists on having a fall-back position for cases when no FO is immediately available, it must first analyze its own incident reports. This will give insight into the appropriate gpm to have as an operating guideline for pump operator and hose crew to react to in a "standard" way.