I agree with Chris and Ralphy, in a manner of speaking. The size of any remote area is the "Feel Good" size a committee decided upon as acceptable. 3-5Psi short Is it really a problem? If your insurance underwriter had to give a value to being that much below the supply curve, would it really kick up your rate a lot? X$ per pound below the hypothetical supply.
If you've done everything pipe and orifice wise to max out your system, just for chuckles turn of one head and re-calc, or two if that's what it takes to put you back above the line. In real life if you had 17 heads in the remote area, and the fire wasn't stopped by the first 15, what are the odds that those other two were going to stop it. (Most fires are controlled with fewer than 4 sprinklers) Using the same info above , but with 5 or 10 Psi extra, if the fire opened all 17 heads what are the odds it was going to stop there, and not open another 10 or 20? I agree that we set the minimums as a way of uniformly applying the standards. But another way to think of it is this. The 500 Gpm hose allowance what good is it? If the sprinkler system controls or extinguishes the fire with the number of design heads or fewer, why would you ever need 500 GPM? And conversely if the sprinkler system failed to control or extinguish the fire with the maximum number of design sprinklers what makes you think there's still going to be an additional 500 GPM flow available with 17 or most likely more sprinklers flowing on an available supply basis? While we like to use the worst possible water supply conditions for the design of our systems, how do we ever know what the worst could be? (No water at all?) Run a Flow test at 2 am and see if you've got that 5 psi back. Would I use that data? NO but some would say if we are to design for the worst water supply conditions then every job will have pumps tanks and emergency generators. But they don't so we've already accepted some level of risk. Our standards say 1500 or 3000 SF design area will work which history supports, but in reality how many more buildings would we actually lose if we only designed to 5 heads flowing? Since statistics say that is 1 more than most fires are contained or controlled by. Thom McMahon, SET Firetech, Inc. 2560 Copper Ridge Dr P.O. Box 882136 Steamboat Springs, CO 80488 Tel: 970-879-7952 Fax: 970-879-7926 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Chris Cahill Sent: Thursday, September 24, 2009 1:13 PM To: [email protected] Subject: RE: Inadequate Water Let me rephrase for Ralphy. Last week we spoke about failure causes. What I think he is trying to convey is if the valve is open statistically nothing else matters. OK it's not that simple but 3-5 lbs under on a theoretical calc vs. a real world fire don't show up in failure data. There are many many reasons for this. Including some fudge in the HW many times, some fudge in the C factors(more so on newer systems), k factors, density actually required, and density actually delivered especially on the first couple heads that open. If the hazard and design density are in sync and the valve is open and something caused the City supply to drop 5 psi and the original RA was 0 safety and the fire starts in the RA does anyone really think the building is going to burn down? I don't. I also don't design like that, it is one link in the failure chain I can control. Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. 763-658-4483 763-658-4921 fax Email: [email protected] Mail: P.O. Box 69 Waverly, MN 55390 Location: 4439 Hwy 12 SW Waverly, MN 55390 _______________________________________________ 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) _______________________________________________ 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)
