Does sprinkler protection beneath an open grated mezzanine change the ceiling level sprinkler design density?
e have a building with a storage room with a grated mezzanine at 8' AFF. Beneath the mezzanine is Class I-IV storage on shelves to the bottom of the mezzanine and on top of the mezzanine is similar storage to 10' high. NFPA 13 requires sprinkler protection for open grating over 4' in width but there is no indication on if this affects the ceiling sprinkler design as it might for in-rack sprinklers. My feeling is the system would have to be designed as if it was ~18' high storage with heads under the mezzanine that match that density, but I am not sure if this is correct or if there would be a benefit to covering the grating entirely and possibly considering it storage under 12' below and above. Thanks in advance for your take. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
6 Comments
Pete H
10/24/2023 06:56:03 am
Treat the mezzanine in this case as a separate floor.
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Pete H
10/24/2023 07:27:38 am
That said, due to the open grating, I agree that a permanent cover over the open grating would be required or at the VERY LEAST water shield heads to be used for the system under the mezzanine to establish heat collection.
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Jesse
10/24/2023 08:08:04 am
The density requirement for the ceiling doesn't change. Storage become high-piled storage at different heights for different commodities. Class I-III at 12-ft and Class-IV at 10-ft.. It sounds like the governing hazard class sin this area would be OH2. If so, you could get by with an OH2 design in this area, but I would probably design the ceiling the same throughout presuming homogenous storage, and then OH beneath the Mezz.
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Dan Wilder
10/24/2023 08:23:52 am
If it's just open metal grating, with no other horizontal barrier separation or sprinklers within a rack, no I would not apply a storage height reduction. The sprinklers are there to provide protection below the obstruction, not to protect the commodity (directly) or to be considered a horizonal barrier to lessen the storage height.
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Glenn Berger
10/24/2023 08:32:41 am
Your approach is definitely acceptable. That is based upon storage for the entire height of the facility with matching design criteria used below the mezzanine (obstruction).
Reply
Anthony
10/24/2023 08:48:53 am
Open grating is considered a full obstruction
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