American Fire Sprinkler Association
12750 Merit Dr., Suite 350 Dallas TX 75251
Ph: (214) 349-5965 Fax: (214) 276-0908
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TECHNICAL UPDATE
September 5, 2007
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"I have a scenario in a 53 story high-rise building where there are
pressure reducing valves servicing zone controls, pressure regulating
valves servicing hose valves, and a high pressure pump servicing the
entire sprinkler system. Is there a visible way to determine a floor
level at which one could stop utilizing the pressure reducing and
pressure regulating valves?"
We have reviewed NFPA 13, 2002 edition and NFPA 14, 2003 edition, and
NFPA 20, 2003 edition as the applicable standards. Our informal
interpretation is that generally the upper six to ten stories will be
less than 175 psi depending on the hydraulic calculations and the
supply from the fire pump.
The requirement from NFPA 14 is that the two most remote outlets on
the standpipe must have a minimum of 100-psi outlet pressure while
flowing 500 gpm. The maximum outlet pressure from 11/2 in. hoses is
100 psi and 175 psi for other hose sizes according to section
7.8.3.2. This along with additional standpipe risers is the driver
for the remainder of the design. When determining if pressure-
reducing valves are needed, also consider the pressures created from
the pump during churn. We know that from NFPA 20 that the fire pump
should not exceed 140% of the rated pressure while at churn but this
will vary depending on the impeller used. So, if the pump must supply
at least 100 psi from the outlet while flowing 500 gpm, the pressures
created at churn can be from 120 to 140 psi. Since fire sprinkler and
fire hose components are rated at 175-psi maximum pressure, this
leaves a pressure difference of 35 to 55 psi from the churn pressure.
A calculation of these pressures to elevation (divide by 0.433 psi/
ft) shows approximately 80 ft and 127 ft. If there is 12 ft per
story, then this equates to roughly six to ten stories. The other
consideration is the pressure from the outlet of the Class I hose
connections where the NFPA 14 standard caps it at 175 psi. Be aware
that if 175 psi is provided from the hose outlet for firefighting
use, the hose will be so hard or stiff that the firefighters will not
be able to bend the hose, thus reducing the capability of the
firefighting operations. Section 5.1.2 requires that the authority
having jurisdiction shall be consulted regarding the required type of
system, class of system, and special requirements and this is an
opportunity to discuss the acceptable maximum outlet pressures from
the hose valves. This may lead to pressure reducing valves needed for
hose valves on the upper floors but not necessarily on the sprinkler
systems. In closing, there are several factors affecting where
pressure reducing valves are placed but generally the upper six to
ten stories will not require them.
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Technical Update is prepared by the Technical Services Dept. of the
AFSA: Vice President of Engineering and Technical Services Roland
Huggins, a PE registered in fire protection engineering; Phill Brown,
a NICET IV certified automatic sprinkler technician and NFPA
Certified Fire Protection Specialist (CFPS) and Tom Wellen, a degreed
fire protection engineering technologist. This is provided with the
understanding that the AFSA assumes no liability for this opinion or
actions taken on it and they are not to be considered the official
position of the NFPA or its technical committees.
Copyright (c) 2007, American Fire Sprinkler Association. All
Rights Reserved
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