Author’s note: This article is written in U.S. measurements (U.S. gallons/pounds per square inch of pressure) as that is how the nozzles and appliances are manufactured. There are often errors in conversions when liters are converted to gallons or vice versa, if imperial gallons are mistakenly used as the measurement, or when nominal measurements are converted literally. This article also discusses the application in regard to 1.75” hoselines, not 2.5”. Many benefits listed for the 1.75” apply to the 2” and 2.5” hoseline as well, with even greater benefit in some cases.
Fire departments have seen or are starting to see the reversion of the service’s tactical culture back towards engine work. Hose and nozzles, and confinement and extinguishing are attractive topics. The idea of a smooth bore paired to high quality hose intrigues firefighters and officers who envision a more effective fireground. They are looking to make things easier for their members, and to create and maintain survivable space for any possible fire victims. There is a valid case for the return to low pressure lines, but often the conveyance is where the message can be lost. Undoubtedly, whether smooth bore or a combination fog, a 50 psi nozzle flowing greater than 150 GPM being pumped correctly and placed accurately has many benefits and is the premier choice for handlines when considering effectiveness and safety.
What has the fire service been doing?
Many fire departments are using combination fog nozzles that operate at 100 PSI to flow 95-125 GPM maximum in a selectable gallonage combination nozzle. This gives a nozzle reaction (NR) force of 48 to 63 lbs. This flow rate can be effective in many applications. A room and contents fire in a dwelling is often easily managed by this flow. Once that room reaches flashover, results will diminish. Results are impeded further when the fire extends beyond the room of origin, and the structure itself becomes involved in fire. Fire departments using these nozzles will frequently find themselves fighting the fire, not simply extinguishing it.
Legacy and modern
Bear in mind, legacy often refers to furnishings of the 1970s and earlier, prior to the dominance of synthetic materials. Wood, cotton, and typical class ‘A’ materials with lower heat release rates were commonplace. Underwriter Laboratories, NIST, and others, have all released data on legacy versus modern furnishings, legacy versus modern construction materials, legacy versus modern fuel loading, and legacy versus modern building layouts. The synopsis of the research is simple: rooms are now larger, rooms hold more fuels than before, and the fuels in the rooms have a higher heat release rate during combustion. The rate of 95 to 125 GPM does not have the same extinguishing effect it used to. This is a driving influence to increasing flow rates at structure fires.
What is a reasonable flow rate to switch to?
It is commonly accepted that 150 to 175 GPM is the sweet spot for flow from a 1.75” handline. NFPA, and many subject matter experts support this target. Multiple departments have conducted thorough nozzle evaluations with findings that correlate and support the 150 GPM and higher theory.
Flow rate is not the sole solution to a better extinguishment. Manageability is as important, if not more. The accurate placement of a water stream is the only factor that determines if the volume delivered will provide extinguishment. A difficult to manage hoseline will prohibit nozzle management and water placement, making the increased volume a nil effort.
The lowest industry accepted nozzle pressure is 50 PSI and the highest accepted flow rate for a nozzle has to do with the hoseline behind it. John Freeman developed the ‘Freeman Ratio’ for smooth bore nozzles in the late 1800s. The Freeman Ratio states that the (smooth bore) nozzle outlet diameter should be half of the hose’s inside diameter. This results in a four times increase in water velocity from hose to nozzle. Half of a 1.75” hose is 7/8. A 15/16 nozzle is .9375 of an inch, and doubled is around 1.88”. The 1.88” is a common actual diameter of marketed 1.75’’ hose. The 7/8” and 15/16” smooth bores flow 160 and 185 GPM at 50 PSI respectively. When considering both the lowest operating pressure and the highest recommended flow rate for a hose size, a 15/16” at 50 PSI is at the top end for flow and manageability. The 7/8” nozzle has a nozzle reaction of 59 pounds, and the 15/16” has a reaction force of 69 pounds. One is slightly higher and one slightly lower than the 125 GPM at 100 PSI (NR of 63 lbs). This uses substantially more water, with minimal change in nozzle reaction. A 100 PSI stream will have a higher stream velocity, but maintaining the desired flow rate of 150 GPM or higher does not equate to a desirable nozzle reaction force. Selecting a nozzle and target flow rate requires additional research beyond this article. It is the opinion of myself that the 7/8” smoothbore at 50 PSI is the optimal balance of flow, impact, and nozzle reaction. The 15/16 should not be disregarded either, as the additional 25 GPM is a fair return on investment for another 10 lbs of nozzle reaction through the same size (nominal) hoseline.
Readers should note that the Freeman ratio can be used in application with fog nozzles as well. Take the ratioed smooth bore flow and consider that as the appropriate fog nozzle flow and pressure for that hoseline. In the case of a 7/8” smooth bore, the equivalent would be a 160 GPM at 50 PSI combination fog nozzle. Trying to get more water out of a Freeman ratioed hoseline results in substantial friction loss increases. Flowing much less only results in unneeded water weight and lower tube velocity which would otherwise help kick out kinks. If you plan on sticking with 125 GPM, stay with a 1.5” hose.
How does the lower pressure increase firefighter safety?
Fire fighting is inherently dangerous as we know, but if something as simple as a new nozzle can drastically reduce our risk, then it becomes sensible to make the switch. The U.S. Fire Administration (USFA) publishes all reported U.S. firefighter line of duty deaths (LODDs), including cause of death. At the time of writing this, the USFA LODD data includes reports for 3643 deaths from Jan. 1, 1990 to current. One thousand four hundred and sixty two (40 per cent) are declared as heart attack or heat exhaustion as the cause of death. This data does not take into account cancer related deaths.
The lower pressure with higher flow rates results in a more rapid fire suppression with less nozzle reaction. This minimizes working time overall, reduces interior temperatures much more rapidly, and reduces exertion by firefighters. There is no real data to correlate, and it is very presumptive, but one can formulate that reducing working time and working conditions will be favourable for firefighters working in the environment. It also makes the fire environment more tenable for possible victims by quickly controlling fire and reducing its effects.
Change must be system wide. Unfortunately, many view the nozzle as the sole piece of the puzzle. There is one significant downside to halving the nozzle pressure; the hose may become “whippy.” One hundred PSI maintains significant rigidity, minimizing hose whip. Flowing in the 150 or 160 GPM-plus range at 50 PSI results in lower nozzle reaction than 100 PSI, but the lowered residual pressure does not maintain hose rigidity. It is up to the construction of the hose to maintain rigidity at the lower pressure. The only real way to determine if your hose is adequate is to test it. Nearly every hose manufacturer has an ‘anti-kink’ hose construction like the Matex Cobra Combat fire hose.
It is worth noting that higher pressures in 2.5” hose actually restricts nozzle movement due to the mass of the water in the line. The 2.5” is very difficult to bend and maneuver at 100 PSI. A beneficial consequence of the mass of water in a 2.5” hoseline is that hose whip will not be induced by common 50 PSI flow rates. The hose does not require the same rigid construction features and although some hoses are better than others, nearly all common 2.5” hoses will support a 50 PSI nozzle without hose whip.
What can you do right now?
Use the 2.5” more liberally. Knock it down. If you’re not flowing enough, you’re not flowing enough, so pull the big line when you need it, reset the fire, and get to work with the 1.75”. No shame in doing the job well with what you have.
Seek out a demo. Companies like Elkhart Brass and their Canadian dealers typically offer free hands-on demos which include flow testing, trialing different hose/nozzle combinations, and getting to try out many various appliances.
Wholesale change can be expensive. Start with hose. Purchase a unique colour and use it as the nozzle section on each preconnected hose line. Once you have a stronger, kink-resistant hose on the nozzle section, you can slowly start purchasing 50 PSI nozzles. From there, replace hose on a regular basis and you can change a single apparatus up to a large fleet at whatever pace works for your budget.
The information and wisdom written above has been collected from numerous fire service mentors and instructors, whose names would generate a list to large to fit.
Joey Cherpin is the deputy fire chief in Edson, Alta., supporting the paid-on-call membership. He runs a small training company that focuses on rural operations and hosts the annual training conference Engine Company Fundamentals.
