We are designing a project which has Ordinary Hazard with unique beam pockets.
We have ceiling pockets which are 988 cubic feet (28 m^3) and so sprinklers are provided within them. The beam depth is large at about 4-feet (1.2 m). Each beam width is about 1-foot wide (300 mm). The beam center-to-center distance is 6'-6" (2 m). Are sprinklers needing to be provided below the bottom of the beam, or not? If sprinklers need to be provided below the bottom of the beam, what is the coverage area if sprinklers are already provided in the ceiling pockets? Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
7 Comments
andrew k
4/30/2021 08:24:30 am
If you can measure from each sprinkler to the CenterLine of the adjacent beams(in both directions) and maintain proper sprinkler coverage (probably 130sqft or less) then we can consider the "beams as walls" and coverage below beams is redundant and not required.
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Franck
4/30/2021 08:39:06 am
I don't know if we can consider the beams as walls, as there might be storage, equipment, etc. undernetah that would not be properly wetted by the sprinkler system. If it was a unique beam, it could maybe considered acceptable, but with multiple occurence, you may not control the fire underneath and finally overtax you ceiling sprinkler protection by opening too many heads, as the fire couled spread in the "unwetted alleys" below the beams.
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Franck
4/30/2021 08:34:56 am
Personal interpration
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Mike
4/30/2021 08:48:38 am
No you don't. Space within the pockets. Max Deflector distance is 22".
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Dan Wilder
4/30/2021 10:03:50 am
I'm missing something I think....
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Casey Milhorn
4/30/2021 01:10:47 pm
If I am clear on the situation, you would just apply the "4' rule" as most designers call it. There isn't a diagram or drawing in NFPA 13 for this rule and you might be surprised how many designers don't know this rule, I believe mainly because it doesn't have a diagram or drawing in the book. It's in the first part of the obstruction rule section. I can't see how this wouldn't apply to this situation. As far as spacing, you are still covering floor space, so you will max out at 15' along the pockets (depending on the length of the pocket) and be 6'-6" between heads the other way. If the concrete tee rule can be applied, you might be able to skip every other bay. You could also technically use the obstructed construction rule to save a little pipe on the sprig length, but being 22" down doesn't really help anything other than that. The beam will still be an obstruction at 4' deep.
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