Had an engineer for a Wal-Mart project (wanting to use a
preaction system outside in their garden center to avoid the higher water demand
of a dry system) run the Fire Dynamics Simulator (FDS) fire model on a few
scenarios with differing RTI’s with a small cross wind as the worst case
scenario and
they could not prove even to themselves
(much less myself who questioned the use of a preaction system
outside where the detection system would be essentially useless thus relying on
a sprinkler to activate on dry pipe...) that the heat detectors (we eliminated
smoke detectors for obvious reasons - remember this is outside with winds...)
would open the valve in enough time to warrant eliminating the system acting
like a dry system.
They were allowed a preaction outdoors, but not
without the 30% increase as was justified in the model I made them check into
for verification. They kept the detection system for their own reasons, it just
was not recognized as a preaction system – just a dry system with fire
detection. Would probably be prudent for NFPA to consider putting some kind of
limitation on the use of preaction outdoors as I had done (i.e. outdoor
preaction system design area of operation shall be hydraulically calculated as a
dry system)… or at the very least investigate this issue ~ heck, even 120-3-3
should at least have such an amendment
