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Remote Area with OH & LH sprinklers

Remote Area with OH & LH sprinklers

(OP)
I have a mixed use Retail/Residential building protected per NFPA 13. I am calcing the retail area at 0.20 gpm. The space is not large enough to get the full 1500 sq ft so I have a few heads in the adjacent corridor in the calcs to make up the difference. I have attached a screenshot for reference. Normally, I calc the OH heads at 0.20 gpm/sq ft and the LH heads at 0.10 gpm/sq ft. However, the engineer has asked me to calc the LH heads at the 0.20 gpm rate since the wall separating the two areas is not a rated wall. The problem I have with this is that the LH heads are spaced for LH occupancy so they will become the most demanding sprinklers (14 ft x 12 ft spacing = 168 sq ft x 0.20 gpm = 33.6 gpm as opposed to the OH heads at 125 sq ft x 0.20 gpm = 25 fpm). This doesn't seem right, but I cannot find a foothold in the standard to begin the "discussion". 2013 edition is the adopted standard and it reads "Each sprinkler in the design area and the remainder of the hydraulically designed system shall discharge at a flow rate at least equal to the stipulated minimum water application rate (density) multiplied by the area of sprinkler operation (23.4.4.6.1)" This seems to support his request. Any help out there?

Micah Davis
Dynamic Fire Designs
www.dynamicfiredesigns.com

RE: Remote Area with OH & LH sprinklers

I would point him to Table 8.6.2.2.1(b) where you cannot calculate a SSP for OH at 168 sq.ft.

He is correct in that the pressures must balance but wrong that a light hazard area must be calculated as ordinary hazard.

Also look at 11.1.2. It appears you have a barrier so you should be able to use the different densities as that wall should prevent heat from passing through.

RE: Remote Area with OH & LH sprinklers

(OP)
Thank you, NewtonFP. The 11.1.2 section was what I was looking for. Even though the wall is not rated, it prevents heat from the OH area from fusing the heads in the corridor.

Micah Davis
Dynamic Fire Designs
www.dynamicfiredesigns.com

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