Call the last 15 minutes of water even more fluff if you want. I happen to have the opinion (and there's nothing but personal 'engineering judgment' backing it up) that option#3 [Hydraulically Calculated Demand (Demand Calc) x Time] affords the most reasonable safety factor for the tank design. But the clarification in the standard is needed especially for the lawyers.
Mark -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Thom Sent: Thursday, August 11, 2011 5:48 PM To: [email protected] Subject: RE: Water storage/NFPA 13 Proposal If your fire was not under control, and being extinguished by the FDP at 45 minutes, it won't be at 60 minutes either. The same can be said for 75 minutes vs. 90 minutes. Those last few min. of tank supply are the least important minutes. If your fire dept. doesn't have this thing out by 45 min. it's time to fall back, pull out the marsh mellows and dogs. Sprinklers work, when they control the fire early, and the FDP response times are prompt. It doesn't matter what tank sizing you used, if this thing has a fire you'll be WRONG no matter what, and there will be plenty of lawyers to say so. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Mark Sornsin Sent: Thursday, August 11, 2011 2:39 PM To: [email protected] Subject: RE: Water storage/NFPA 13 Proposal Bill: I agree #1 is the easiest; but it can also result in tank sizes considerably smaller than #3, which represents the actual design flow. Local conditions can really alter the amount of overage a system design might include - overage could range from 5% to well over 50%. Given that I am unaware of problems where the tanks were undersized, I am reluctant to believe we need the added volume required by #4. As for having to do a design ahead of time, I don't see that as a real problem. That's part of engineering (whether you're a NICET designer or a PE). The fact that tanks normally come in standard sizes usually affords some 'fluff' so that you don't necessarily have to have the exact final design of the system prior to sizing the tank. Mark A. Sornsin, PE| Fire Protection Engineer Ulteig Engineers, Inc.| Fargo, ND [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bill Brooks Sent: Thursday, August 11, 2011 7:34 AM To: [email protected] Subject: RE: Water storage/NFPA 13 Proposal I see four possible calculation approaches for the sprinkler demand part of tank sizing: 1. Minimum Density x Tabular Design Area x Time 2. Minimum Density x Actual Design Area (developed using the 1.2 rule) x Time 3. Hydraulically Calculated Demand (Demand Calc) x Time 4. Hydraulically Calculated Demand (Supply Calc) x Time I intend to submit a Comment to clarify this. #1 is the easiest for everyone, the others require the sprinkler system to be fully designed before the tank size can be confirmed. It's also evident that all of the methods other than #4 will mean draining the tank in less than the required time duration. Then of course is how to decide whether to use 60 minutes or 90 minutes or something in between for OH. Bill Brooks William N. Brooks, P.E. Brooks Fire Protection Engineering Inc. 372 Wilett Drive Severna Park, MD 21146-1904 410-544-3620 410-544-3032 FAX 412-400-6528 Cell in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
