I’m a Fire Inspector/Design Reviewer and I have a problem that I’ve been trying to tackle. NFPA 14 systems are designed for high volume low pressure firefighting tactics, but the majority of fire departments in America use high pressure low volume equipment. Here are the key points:
NFPA 14 Type 1 standpipe systems provide 250 gpm at 100 psi with 200 ft to most remote location in a sprinkled building. In the firefighting world this equates to a fire attack with 250 ft of 2.5” hose and a 1-1/8” smooth bore nozzle. The 250 ft comes from, 50 ft to stretch to the hose connection on the floor below the fire floor and 200 ft to most remote location on the fire floor. Fire ground friction loss calculations for 250 gpm through 2.5” hose is 15 psi loss per 100 ft. A smooth bore nozzle requires 50 psi to operate properly. We are stretching from the floor below so we have roughly 6 psi head loss. So the required pressure at the hose valve is 93.5 psi. You can see that the NFPA 14 design requirements are in line with the use of this higher volume lower pressure equipment.
The problem is that 2.5” hose is very heavy and requires a lot of man power. 2.5” attach lines are used by large city departments like Seattle, New York, and Chicago. Many smaller city and town departments don’t have the staffing to stretch such big lines. We may only have a couple firefighters stretching an attack line where as the big cities would have 6 or more. So we use smaller more maneuverable hose and more pressure demanding fog nozzles.
A more typical firefighting set up in the majority of fire departments would be 1.75” or 2” hose and a 75 psi or 100 psi fog nozzle flowing between 150-200 gpm. I’ll use Bozeman as an example. We use 1.75” hose, a 75 psi fog nozzle, and a target flow of 175 gpm. In our experience the pressure loss per 100-ft of 1.75” hose with 175 gpm is 50 psi. So if we need to stretch 250 ft of hose, we would need 206 psi at the hose valve on the landing below the fire floor. Add in that the tallest building we have is 11 stories, and a 25 psi pressure loss adjustment for pumping the FDC, and we are up to 285 psi required at the FDC.
There seems to be a disconnect between the design world and the firefighting world. This poses all sorts of problems such as compromising sprinkler systems and old standpipe systems since they may have components that are not rated for such high pressures. Even worse are systems with pressure reducing hose valves that wouldn’t even allow us to pump the FDC to get anywhere near the pressures we need with our equipment (see One Meridian Plaza fire in Philadelphia).
I think that Fire Departments need to communicate their design needs to designers, and Fire Departments also need to look at the equipment they use, and see how they can make changes to operate more closely to what NFPA 14 systems are designed for.
If you have any knowledge on this topic I would love to hear it, thanks in advance.
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