I concur with Mark (and not just because we PE's must stick together)
The original proposal was a 12 ft deep pocket. Considering that is
basically the height of a story, the committee felt it appropriate to
assign a lower value. I would first approach allowing a small
increase in height based on the modeling (see out web site for a copy
of the report) and the very small volume.
Our position has been that ceiling pockets or even openings in a drop
ceiling that are narrow and along a wall are not a problem. We have
arbitrary picked 12 inches as a maximum width until we do some
modeling. I picked this because other than a curtain fire, the center
line of the fire plume is not directly against the wall. With it being
in the center of the fuel package, even a small chair at 2 ft wide
will be at 12 inches form the wall. AS such, a adequate amount of the
heat will be captured by the lower ceiling.
Naturally discuss this with the AHJ since it has not yet been
addressed by the 13 committee. Additionally, as a member of the
technical committee i need to say, this is not to be considered a
formal interpretation by NFPA or any of its technical committees.
Roland
On Aug 26, 2008, at 12:01 PM, Mark Sornsin wrote:
I am going to go out on a limb and say "No" this should not require
sprinklers within. Unfortunately, there is nothing absolute to back
me up, at least in NFPA 13.
I would argue that the ceiling jet from a fire is not going to
'notice' such a narrow gap. Also, whatever amount of heat manages to
'escape' into this void space will quickly fill it, due to its
miniscule volume. So I guess I would try to use reason and note that
the ceiling pocket rules of NFPA 13 allow a volume of up to 1,000
cu. ft. this volume is less than 10% of that.
But I think the small width of the gap is the bigger reason it won't
affect the activation of the ceiling sprinklers.
Those in the know may now feel free to rip apart my argument.
Mark A. Sornsin, PE
Fire Protection Engineer
Ulteig Engineers, Inc.
Fargo, ND
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