My point is that there are already so many factors of safety built into the design of a system that one more is overkill upon overkill. 95% of fires are controlled with one sprinkler operating, 98% of fires are controlled with five or less operating, yet we calculate 1,500 square feet (or 3,000 square feet for military projects), them we overestimate the friction loss in pipe and fittings, underestimate the water supply, them worry about adding an additional cushion.
Please, no "what about the other 2%" comments. Paul J. Pinigis, P.E. Chief Life Safety Engineer -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of George Church Sent: Friday, March 16, 2007 9:56 AM To: [email protected] Subject: RE: Minimum Supply Pressure Well, there ARE a few more considerations. Was the supply adjusted for lowest tank gradient? What confidence level do you have in the accuracy of the test data ? What confidence level do you have that NO additional 90's will be added? What is the Owner's tolerance for risk? NFPA #13 does NOT require a cushion. Good trade practice, flexibility of installation changes, common sense, and protection of your boss's retirement assets require a cushion of some sort. So may the various AHJs you face- water co, fire and code officials, insurance carrier, etc. So you could be right and fine with .0001 cushion- but in so doing, you may find yourself in a box scratching for 2.7 PSi in a .0001 margin when a duct doesn't go in as planned, some cable bracing is discovered, ANYTHING. We deal with a water company that applies a .8 coefficient to all hydrant test. If your test was from a .7 hydrant, the supply is overstated and your system, upon correction, would be 5 or 6 PSI shy. Or if the tank level was 3' above lowest tank gradient, your system won't work in August. Or 4 heads could control the fire and everyone smiles. We just don't know EVERYTHING and we can't look into the future. I have trouble sleeping when we don't have 10%, and prefer 15 PSI+ on prelims on bid day. We just analyzed a new site for a customer wanting to use K25s without a pump- would you tell him, based on 3.6 PSI cushion and ignorant of bar joist spacing, that it would? We're proceeding with a pump, and if things turn out better we can omit it, give him a credit for the pump, take some back with the $^ of k25's, but at least the money's in the job to start with. When I was assetless and worked for others, I'd consider installing what you have. Now, not without everyone involved knowing it, and not if I was on the hook for the pump or larger piping replacement, or dual feed mains, or whatever was needed to fix whatever changed and bumped us up. Imagine going to an owner with a $50,000 adder and explaining it with "we had to add a 6" 90 at the top of the riser." Not a situation I'd look forward to ! glc -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Pinigis Sent: Friday, March 16, 2007 9:31 AM To: [email protected] Subject: RE: Minimum Supply Pressure If you can achieve 10% without spending your client's money (or your own) great, but it is not necessary. Paul J. Pinigis, P.E. Chief Life Safety Engineer -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Brian Harris Sent: Friday, March 16, 2007 9:29 AM To: [email protected] Subject: RE: Minimum Supply Pressure 10% is what we go by, based on your numbers your only at around 2% :( Regards, Brian Harris First Defense Fire Protection Design Engineer [EMAIL PROTECTED] 704.948.3506 phone 704.948.3507 fax -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Charles Thurston Sent: Friday, March 16, 2007 10:19 AM To: [email protected] Subject: Mininum Supply Pressure Hello All, Let me be the one to start things today. What is the minimum safety pressure allowed ? I have looked in 13 and did not find it.... I have a situation where the safety pressure is 0.913 psi. Basis is: Hose 250 Static 67.00 Residual 38.00 @ 920.00 Available 40.128 @ demand of 882.87 Requires 39.215 psi Leaving a safety of 0.913 psi -- Best regards, Charles mailto:[EMAIL PROTECTED] Coastal Fire Protection _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum
