Not much help here, but I try to remember the fact that Hazard
Classifications are based on the quantity, combustibility, and heat release
rate of the CONTENTS.

I think the physical challenge of attic fires are light weight wood
construction combined with the acute slopes, fires getting through at the
eaves making them more undetectable until they are in a position to burn
fast and hot. The presence of mechanical equipment just creates more
obstructions, shielding, etc., so if I were King I would decree "Use the LH
rules except bump them up 1.5X"    :)





From: Sprinklerforum []
On Behalf Of rongreenman .
Sent: Thursday, October 13, 2016 11:50 AM
Subject: Re: Ordinary Hazard Attic Spacing


Opinion: Attics are light hazard but seem to have become something between
light and ordinary (probably a good thing). So if it's emptyish it's an LH
with the attic modifications. If there's stuff in it that makes it OH, it's
OH. Kind of like when does a platform used as a stage actually turn into a

On Thursday, October 13, 2016, James Litvak <> wrote:

This question goes past the one I just posted. This question assumes an
attic with mechanical equipment in it is OHI. 


So, in an ordinary hazard attic, does regular OH design? After all, the
increased start pressure only applies to light hazard CC spaces. There's
nothing different specified for OH. Therefore, in a LH attic spaced 15'x8'
the remote sprinkler demand is 14.8 gpm at 7 psi, with a 5.6K sprinkler.
Spaced 10'x12' the remote sprinkler demand is 25.0 gpm at 20 psi. In an OH
attic spaced at 130 sq.ft. the remote sprinkler demand is 19.6 gpm at 12.1
psi. It seems strange that a LH attic would have a higher remote sprinkler
demand than an OH attic. Am I missing something in the code that allows that
to happen? 

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