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
January 16, 2009
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"Is a single interlock preaction system considered a 'wet' type
system? As noted in 2002 Edition, it is not required to increase the
design area by 30 percent for a single interlock preaction system? If
so, can the area reduction for QR sprinkler be used?"
We have reviewed NFPA 13, 2007 Edition that you indicated as the
applicable standard. Our informal interpretation is that NO, a single
interlock preaction system is not a wet system. This is clearly stated
in Chapter 3 Definitions. As an example, 3.4.1 defines an antifreeze
system as a type of wet system. It does not do this in its definition
in 3.4.9 of preaction systems.
You are correct in that a single interlock preaction system does not
have to have its hydraulic design area increased by 30 percent, as
required in a double interlock preaction system. There is a
fundamental difference between the two types of preaction systems and
that is the double interlock system has pressurized air in it while
the single interlock normally does not. A single interlock system
admits water to sprinkler piping upon operation of detection devices.
As required by 7.9.2.8.1.1, the detection system has to be designed to
operate prior to sprinkler operation. This normally will allow a
single interlock preaction system containing no pressurized air to
respond in a time very close to a wet pipe system.
Your question of using the area reduction for the use of quick
response sprinklers allowed by section 11.2.3.2.3 is one that could be
considered. You can justify this by using Section 1.5, Equivalency.
This would have to be negotiated with the AHJ. Section 11.2.3.2.3
clearly states that the allowance applies only to wet systems and the
use of quick response sprinklers. If it can be demonstrated that the
water will discharge within the same time frame from a single
interlock preaction system as from a wet system, it would be feasible
to call it equivalent.
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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 ⌐ 2009, American Fire Sprinkler Association. All Rights
Reserved
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