By BRIAN BRUSH
“Arguments for and against the use of various nozzle designs often become nullified on the fire ground as crews find they cannot safely operate lines which exhibit high nozzle reaction forces.”—Captain David P. Fornell
NOZZLE OPERATING PRESSURE
The smooth bore nozzle may be viewed by some as “dated,” but if you take a little deeper look at history, you can see some very sound reasoning in the smooth bore nozzle. The operating pressure of the smooth bore is a range from 40 to 60 pounds per square inch (psi), with 50 psi as optimal. This was important to our forefathers in the fire service, as early pump systems were primarily lower pressure and could see significant fluctuations with more than one line being supported simultaneously. The solid stream and long tip provided accurate delivery of the fire stream at a great distance for firefighters with limited personal protective equipment.
As technology advanced, our pumps were able to provide higher and more consistent pressures. Lloyd Layman and various others brought the fog nozzle into the American fire service, vendors started to develop automatic nozzles, and before we knew it there was a shift from a 50-psi fire service to 100 psi.
Over the past 15 to 20 years, an increasing number of firefighters and departments are beginning to question what has been gained by doubling our nozzle operating pressures. In many cases, it is being discovered that, for the most part, the only true gain has been nozzle reaction, which simply equates to more work on the nozzle firefighter.
There have been several studies done over the past 20 years into nozzle reaction and how it affects hoseline operations. The goal of these studies has been to identify how much nozzle reaction firefighters can comfortably handle while still being able to effectively advance and manage a hoseline. A study by Paul Grimwood outlined three working limits: one firefighter [60 pound-force (lbf)], two firefighters (75 lbf), and three firefighters (95 lbf). I have been fortunate enough to work with firefighters across the country on hoseline operations, and I can tell you that with good technique, practice, improved fitness, and continued work, firefighters can easily operate lines with nozzle reaction forces beyond the above working limits. However, these working limits are very accurate for the majority of firefighters and the median level of training.
Nozzle reaction is the resultant lbf of pushback from the combined volume and pressure leaving the nozzle. The only way to alter nozzle reaction is to alter the volume [gallons per minute (gpm)] or the pressure (psi). Many people have used a variety of methods to demonstrate nozzle reaction like fish scales and rope, but the actual force is calculated using the nozzle reaction charts. As a rough rule of thumb, the lbf of nozzle reaction for a 100-psi nozzle is half of the gpm.
On the nozzle reaction charts, you can see the amount of nozzle reaction associated with four very common 1¾-inch nozzles. You can also see the side-by-side comparison of a 150-gpm-at-50-psi fog nozzle with a 100-psi automatic fog nozzle. Flowing the same gpm, there is a nozzle reaction difference of 21 pounds at 100 psi; at 150 gpm, the nozzle reaction of 76 pounds is at the working limit of two firefighters. Here is where you need to question if your department sees this as necessary or unnecessary pressure.
With good practices and techniques, firefighters can work beyond the outlined nozzle rea