I would think you'd want to discourage QR in dry systems since the water delay in conjunction with rapidly opening heads would increase the number of open heads by the time water got to the fire (remember using 256 heads in dry systems anticipating hot vertical fires to keep the number of rings opening to "over the fire." Giving a bonus to using QR might increase using QR where you don't want them. Perhaps the concept is that because you have heat traveling differently along slopes than flats you'll have a different number of heads on average (more as Ron F. said) than the number that typically open under flat ceilings. Same issue with dry pipes. I think this is where NFPA builds in the "cushion" AHJs are always trying to impose by requiring higher than necessary pressures. If only 2 or 3 heads opening control most fires then it stands to reason that calculating for 8, 10, 15 or 18 heads in the very most difficult place to get water to those heads results in a cushion in itself. If the area is increased (i.e.: more heads are in the calculated area) when it is likely that more heads may open then these cumulative increases in area compensate for that and maintain the cushion. I really think that if we are expected to believe that every fire forms a rectangle on a 1:1.2 ratio, unless the building on fire is insured by FM and then it forms one with a 1:1.4 aspect, and that the entire area is on fire with the maximum number of sprinklers flowing at all times then the AHJs might be justified and the committee members ought to be, at least, castigated for pushing everything too close to the bone.
On Mon, Feb 7, 2011 at 1:55 PM, Mark Sornsin <[email protected]> wrote: > Not sure I'm following the logic, but I'll give it a shot: > > First, just because there is an adjustment in sprinkler spacing for the 4:12 > slope doesn't mean that adjustment has necessarily negated the effects of the > slope in operating the right sprinklers. So both wet and dry sprinkler > systems are 'charged' a 30% increase for large sloping ceilings. Now discard > the slope issue. > > Apparently, the committee feels it is warranted to 'charge' a dry system > design an additional 30% in area (as compared to wet systems) because of the > delay in getting water to the open sprinklers in dry systems. Makes sense to > me. So whatever you came up with for a wet system design area, if you have a > dry system, add 30% to the area. E.g.: if your wet system area happens to be > 1,950 (perhaps because you have a steep slope) then add 30% to that number to > get the dry system area. > > You seem to be uncomfortable with the lack of QR reduction allowed for a dry > attic system under a steep slope. 200% area increase from a wet system (with > QR reduction benefits) to a dry system (that doesn't get the QR reduction). > Maybe you have a point- maybe the QR heads would open more quickly and > contribute to fire control faster than standard link heads. OR... > > Maybe we have a situation similar to high-piled storage: in that situation we > don't allow QR because we're afraid too many heads will open duet o the high > heat release rate. But you notice we don't offer a larger design area as an > option. Similarly, maybe the issue of heat by-passing sprinklers as it climbs > the slope of the attic ceiling may lead to too many QR heads operating away > from the fire. So the committee prefers that we ignore the QR reduction in > this case. > > Another way to look at it is that the QR reduction is a little 'scandalous.' > Not everyone agrees it is a good idea, even on wet systems (e.g. FM Global). > So for the committee to allow it on dry systems may be considered 'going too > far.' They'd rather have what amounts to be a 200% area increase in a fire > scenario (steeply sloped attics) that has proven to be a challenge for > standard system layouts to control. > > Or maybe it just hasn't been considered in detail. Maybe some fire testing is > in order to prove your point that the design area discrepancy seems excessive. > > Anyone got some money to sponsor a fire test? > > 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 Brad Casterline > Sent: Monday, February 07, 2011 11:51 AM > To: [email protected] > Subject: a glaring inequality in 13? > > I would appreciate thoughts and comments from all willing to take the time: > > Combustible attic, 4/12 slope, 10' to peak. 1500*1.3=1950 for slope exceeds > 2/12. Light Hazard, so QR heads required. If DRY, 1950*1.3=2535. If WET, > 1950*.6=1170. (QR Reduction). Doesn't this mean the area has to be increased > over 200% for DRY, not 30%? For 20' to the peak, 1950*.75=1463~~ 170% > increase for DRY. Using SSU, the increase would be for the exact same spacing > and height in both cases. BB and SD Attic heads 'increase' the area 30% for > DRY (from 5 to 7 heads), but without regard to height, and the slope MUST be > minimum 4/12. They must be within 6" each side of the peak, at 6' > max. SSU also have to be within 6" each side, and 8' max is cheaper than a > pump. I know this has not come up in the 16 months since I discovered the > Forum. If it did before that, I would appreciate being pointed to the > location of all discussion about it. > > > Many thanks, > > Brad > > _______________________________________________ > 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) > -- 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 They are happy men whose natures sort with their vocations. -Francis Bacon, essayist, philosopher, and statesman (1561-1626) _______________________________________________ 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)
