Use of Preaction outside is still a dry system!

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Use of Preaction outside is still a dry system!

Postby Blackstone on Wed Dec 10, 2008 2:18 pm

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 :roll:
We find consulations, we learn tricks with which we deceive ourselves, but the essential thing - the way - we do not find. Listen to the river.

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