NFPA 13R - Garages

[dssprdesigner]

I just have a question about NFPA 13R 7.3.3.1(3)

If I were to use a quick-response dry pendent sprinkler in a 13R single dwelling unit garage, if the head is spaced at 225sq.ft and designed to operate at a 0.05gpm/sq.ft density a K5.6 sprinkler would only need 11.25USGPM @ 4.04psi. a K4.9 sprinkler would demand 11.25USGPM @ 5.27psi. (I haven't found a K-factor smaller in Dry Pendents).

Is the intent of 7.3.3.1(3) to have heads operating at less than 7psi?

 

[SprinklerDesigner2]

No, 7 psi always.

I doubt you will find any dry pendents having a k-factor much under 5.6 at all. With length perhaps you might get one at 5.4 or 5.5 but that is going to be about it.

I am not familiar with the project but I doubt a density of .05 can be used where you are not using a residentially listed sprinkler.

 

[cdafd]

Look at the manufacture sheet also to see what the minimum psi is required for the listing of the head.

Have you looked at ec sidewalks to eliminate need for dry pendant

 

[stookeyfpe]

Unless your sprinkler is listed for Residential installations, your design density is 0.10 GPM/square foot, not 0.05 GPM/square foot.

 

[dssprdesigner]

That's why I find the language of that sentence strange, why have it written that the maximum spacing is that of light hazard designed to discharge at 0.05gpm/sq.ft density.

"7.3.3.1(3) Quick-Response spray sprinkler at light hazard spacing in accordance with NFPA 13 designed to discharge at 0.05gpm/sq.ft density"

Only if you were to use a K4.2 sprinkler would you ever meet the 0.05gpm/sq.ft density and be over 7psi.

NFPA 13R addresses the minimum pressure of Residential Sprinklers (6.4.5) not Quick-Response Sprinklers, and 7.1.2, states where quick-response sprinklers are used in accordance with 6.2.1.3, the discharge and design area requirements of NFPA 13 shall apply. Garages are addressed in 7.3.

Majority of the garages in our area are unheated and we are subject to freezing temperatures (-20F today), which limits us to use dry pendents on wet systems.

I have found a listed residential dry pendent and we are going to use that but I am hoping for dialog on whether or not 7psi is required in 7.3.3.1(3).

 

[dssprdesigner]

The listing of the head nails it down.

 

[TravisMack]

7 psi is the minimum pressure for any sprinkler. So, you would have to meet that. Here in the desert southwest, we use wet systems in these areas, so we can get a 4.2 standard spray QR pendent in these areas so the 0.05 gets us closer to just 7 psi at spacing.

Travis Mack
MFP Design, LLC

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