13R, 3000 sq. ft and travelling up the curve

[skdesigner]

I am designing a 13R system for a 4 storey building. The floors are framed with open-web wood joists, and there will not be sprinklers in the combustible concealed space. Main floor has a large common area, which would force me to calculate 3000 sq. ft. NFPA 13-2010 11.2.3.2.7.2 prevents me from reducing the size of the area in any way, but is it possible to go up the light hazard curve and calc to a density of 0.07 instead of 0.1?

Thanks in advance!

 

[SpcFoor]

What am I missing that you would have to calculate 3000 sqft?

 

[skdesigner]

NFPA 13R 2010 7.2.1 For areas outside the dwelling unit, the design discharge and design area criteria shall comply with NFPA 13, unless permitted by 6.4.7 and 7.2.2.

7.2.2(1) limits the compartment to 500 sq. ft., which my common area exceeds (more like 6000). The pushes me to 13 for design criteria.

NFPA 13-2010 11.2.3.1.4 (3) would require me to calc 3000 as the open web wood joists do not meet one of the exceptions in (4).

Further, an earlier query submitted to the NFPA 13 technical section yielded the following:

Dear skdesigner,

Yes, the minimum 3000 ft^2 (279 m^2) design area in Section 11.2.3.1.4(3) of NFPA 13 (2010 Ed.) applies to the non-residential areas of a building that is otherwise protected in accordance with NFPA 13R (2010 Ed.).

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Fire Protection Engineer
NFPA

Important Notice: This correspondence is not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.

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Create Date: 3/16/2012
Contact: skdesigner

Subject: Design criteria outside dwelling units

Question for NFPA: We have a 3 storey combustible construction hotel that does not require sprinkler protection in the floor/ceiling spaces. Does this force us to calculate a 3,000 sq. ft. design area in an area incidental to the residential occupancy (i.e a meeting room greater than 500 sq. ft.) because it is adjacent to an unprotected combustible space?

Thank you for your time.

 

[TravisMack]

Yes, I go up the curve on those to 0.07 gpm / sq ft. I would also use 4.2k sprinklers if you can. You can cover up to 159 sq ft and still be at 7 psi with 4.2k sprinklers at that density. With 5.6k sprinklers, you are going to over discharge all heads less than 211 sq ft.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[skdesigner]

Thanks Travis, and good call on the smaller orifice sprinklers. They work like a charm with the poor water supply.