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 UDPATE
JULY 16, 2008
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"We plan to replace six existing upright sprinklers with six pendents
on flexible hose fittings. Are hydraulic calculations required?"
We have reviewed the 2007 edition of NFPA 13 that you indicated as the
applicable Standard. Our informal interpretation is that hydraulic
calculations will be needed.
If it is not apparent that the modifications have resulted in a less
hydraulically demanding configuration, it is the AHJ's prerogative to
require hydraulic calculations for the modified area. Section
8.15.19.5 addresses the requirement when modifying (revamping) a
hydraulically calculated system. Unlike the pipe schedule system,
this requires that hydraulic calculations be performed to verify that
the design flow rate will be achieved. The sprinkler handbook confirms
that when a hydraulically designed system is modified, new
calculations must be provided. The change from standard sprinklers to
a flexible hose fitting will create a modified K-factor in the system.
As such, modifications to an existing system from standard spray
sprinklers would require new calculations just like changing from
standard to extended coverage sprinklers. In addition, when you
relocate a sprinkler in a calculated system, it has been modified and
the area of coverage of the sprinkler is likely changed. This could
change the required design flow and pressure of the sprinkler. This is
a very literal interpretation of NFPA 13. Some AHJ's require
calculations for any relocated sprinkler, while most set a threshold
of 5, 10 or 15 relocated sprinklers before they will require
calculations. I would suggest that you consult with your AHJ to see at
what point that calculations are required. The factors that may be
discussed include the equivalent feet for friction loss of the
flexible hose fitting and the safety factor between the water demand
and the available water supply. Many jurisdictions do not require
calculations because they recognize that changes to the assigned area
of coverage is typically small and the greater pressure upstream from
the end head produces a discharge greater than the required minimum.
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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) 2008, American Fire Sprinkler Association. All Rights
Reserved
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