The first interpretation but not for mere fluctuations. More that it's for mathematically degrading systems due to higher anticipated demand (new communities), or deterioration of the entire municipal system due to age (older, established communities). And my understanding is it originated with IRI and was to be applied to the water supply (downgrading the supply by 10%), not the FP systems individually. As is often the case, when the fire service gets married to an idea (like a single head in a kitchen being a system) it perpetuates itself into the lore and the origins, and concurrently, the rationale, are lost to the dim times of pre-history–don't you get it? it's turtles all the way down. Since municipal raters and underwriters could impose such a rule on a municipality, but the fire service couldn't, the fire service shifted the burden to calculations of the individual systems. Although the math for either method is a wash, how does derating the system address the water supply itself? If the purveyor derates voluntarily then the further derating of the system is overkill and expensive, and if he doesn't the system derating is valueless. I think this may be why NFPA never even mentions "safety margins" or "factors." I realize I'm pretty much alone in this interpretation, and I'm not even 100% sure of the origin of the "rule," but 10% degradation of the system hydraulics, particularly with 5 year internal inspection intervals, just makes no sense to me.
On Fri, Jun 13, 2014 at 12:22 PM, Rahe Loftin - 7PMC <[email protected]> wrote: > I have always been under the impression that the safety factor indicated in > specifications for hydraulic calculations was for water supply fluctuations > in sprinkler systems connected to public water supplies. This is also > indicated in the commentary in the NFPA 13 Handbook. > > However, recently a sprinkler contractor was contending that it was to > allow for field piping changes. > > Any opinions? > > *Thanks* > > *Rahe Loftin, PE * > _______________________________________________ > Sprinklerforum mailing list > [email protected] > > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org > -- Ron Greenman Instructor Fire Protection Engineering Technology Bates Technical College 1101 So. Yakima Ave. Tacoma, WA 98405 [email protected] http://www.bates.ctc.edu/fireprotection/ 253.680.7346 253.576.9700 (cell) Member: ASEE, SFPE, ASCET, NFPA, AFSA, NFSA, AFAA, NIBS, WSAFM, WFC, WFSC They are happy men whose natures sort with their vocations. -Francis Bacon, essayist, philosopher, and statesman (1561-1626) A problem well stated is a problem half solved. -Charles F. Kettering, inventor and engineer (1876-1958) _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
