Brad, Here is my explanation of the 100-psi requirement, and I apologize to any one that I might offend with such a long opinionated response. This is my pet peeve, and I have tried my best to educate the fire service as to what they could expect during a high-rise fire condition.
The old standpipe pressure requirement was 65-psi. This changed in the late 1980's or early 1990's after the One Merridian Place fire where two firefighters died whiile they were searching several floors above the fire. The lack of pressure avaiable in the standpipe allowed the fire to grow and extend to their search area. The standpipe system had PRV hose valves installed which were improperly adjusted to a pressure too low for fire operations. The NFPA-14 committee decided that since the automatic nozzles in use at that time required an optimum 100-psi nozzle pressure, that this magic number (100-psi) would be a good starting point. There was a long discussion with numerous tests of various nozzles and hoses. Too little pressure did not provided enough water and too much pressure made it very difficult to manuver the hose around corners. The minimum 100-psi at the hose valve was a "reasonable" pressure to allow "adequate" pressure to the nozzle while flowing a "sufficient" quantity of water taking into account different friction losses for different lengths and diameters of hose that the different fire departments would use. The maximum 175-pis was used to match the existing maximum pressure for the sprinkler systems connected to the standpipe, and also allow a range for minimum and maximum pressures that the PRV's could satisfy. Since then, numerous changes have been made in fire department operations. There are now low pressure automatic nozzles, low friction loss hoses, and many departments just use a non-automatic adjustable nozzle in their high-rise packs. Since the older buildings may only have 50 to 65-psi at the hose valve while the newer buildings have 100-psi, the manufacturers also have produced an in-line pressure gauge that can be installed at the hose valve so the firefighter can see the pressure available from the hose valve and make adjustments accordingly. Presently, it's really up to each AHJ to decide on an SOP for high-rise fires in their jurisdication knowing that the standpipe systems have pressures that can vary from 50 to 100-psi and may be equipped with pressure-restricting or pressure-reducing valves which may or may not be properly set. They need to pre-fire plan the buildings to learn how each building standpipe system was designed. rick matsuda city of dallas -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Brad Casterline Sent: Wednesday, February 19, 2014 8:51 AM To: [email protected] Subject: 100 PSI requirement at top of Standpipe Does anyone know why the technical committee settled on 100 PSI minimum at the 2.5" hose valve? It used to be 75 PSI, and for High Rise retrofit I have seen AHJs accept 75. I am just curious because I think with about 60 PSI at the 2.5" connection to the standpipe we could get about 250 GPM at the nozzle, figuring the Pf for the T, 2.5x0-6 nip, hose valve, and 100 feet of 2.5" hose. A 15 psi safety factor seems reasonable, but 40 psi??? I know the F.D. might want to use a 2.5x1.5 reducer and 1.5" hose, but with 150 GPM flowing through 100 feet of 1.5" hose the Pf in the hose alone is about 162 PSI! So, I don't get it, but I am likely missing some simple explanation, so I'm asking. thanks, Brad Casterline, NICET IV Fire Protection Division FSC, Inc. P: 913-722-3473 [email protected] www.fsc-inc.com _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
