Hydraulic Calcs for Sprinklers above / below Cloud Cielings

[JSCFire]

Do you include every sprinklers above and below a dropped cloud cieling located in the design area in the calculation?

NFPA 13 (2007) section 22.4.4.6.3 indicates that only the above or below level is required to be included in the calc.

This does not seem conservative enough since this open floor plan has rather large spaces between cloud ceilings and many sprinklers both abaove and below.

Any advice?

 

[TravisMack]

If you were protecting under large ducts, would you include heads at both levels, or just one of the levels? I see the clouds as no different. I will calculate the heads at just one level. That is what I understand NFPA 13 to require as well. However, I could be wrong and that - and it wouldn't be the first or last time

Travis Mack
MFP Design, LLC

 

[firepe]

Just my opinion, but I do not believe that NFPA 13 has actually addressed how clouds affect the fire plume, and how activation times and discharge patterns may be affected, nor whether additional heads need to be accounted for in hydraulic calculations.

Short of any guidance from the NFPA 13 committee, the only literal way to look at it currently, is that you are first responsible for protection at the highest ceiling/deck, then, as Travis has suggested, you must add heads for any obstruction to discharge using the available rules in NFPA 13 for obstructions.

This would typically (not always) lead to adding heads into/under any "cloud" or other obstruction that is wider than 4-ft. and obstructs the heads at the higher level.

It is my personal opinion that while this position may be defendable legally, it is not necessarily supported by reality. More testing/study needs to be done to determine the effects of clouded ceilings, since it does not appear that our Architect buddies plan to stop designing them into the projects that we have to protect.