Actually a good question. Generally speaking you ignore the walls (exception the room design of course and others like small systems where you simply add additional water to the calc). The designed system has little to do with physics or reality. I’ve yet to see a pendent sprinkler discharge water in a 10X13 rectangle, the amount of water hitting the flow is NOT equal to the assigned density (even IF it did flow uniformly throughout the pattern which it doesn’t), friction loss through fittings is not well accounted for from an academic standpoint, if you move the sprinkler an additional 6” off a wall it will greatly increase the required pressure but do you think it will really affect the performance, unbounded fires do burn in a relative circle but the design as never been based on that etc etc. The reality of the design is that it is a well defined process whereby different people get relatively similar results AND IT WORKS to control the fire.
As such, for a new design, the approach ensures that a fire located anywhere will be controlled by assigning the remote area in the most hydraulically demanding location regardless of walls. When modifying a system, you will not find anything that relaxes this conservative approach. So if you are looking for a get out of jail card, get comfortably because you're staying in jail. Now as an engineer evaluating a modification, one could challenge the conventions of the standard and I believe still have an adequate system. If one is thinking to avoid lawsuits, don’t be an engineer (or contractor for that matter). I know of a case where the building burned down and the control valve was known to be closed and RECORDED as such for 6 months before the fire.The contractor is still being sued - UFB. Somewhat what Cecil said with a touch of my opinion that is not I say not (think of the big chicken from Looney Tunes Foghorn Leghorn pronouncing that) to be considered an interpretation for NFPA 13 or any other NFPA standard (with a few less THE’s). Roland Huggins, PE - VP Engineering American Fire Sprinkler Assn. --- Fire Sprinklers Saves Lives Dallas, TX http://www.firesprinkler.org On May 20, 2014, at 5:12 PM, Cahill, Christopher <[email protected]> wrote: > I can't believe I'm asking this question after all these years. Anyway, > swallowing pride and asking. > > 2010 NFPA 13 strict Density/Area method 11.2.3.2 and 22.4.4.1.1. Great big > room being subdivided. Existing system with a new wall added between heads on > a BL. Contractor had to add a head on one side to preserve the existing > spacing (area) of the heads. Without head over 130 sq.ft. I take the 1.2 > ^.5 of the area and get 46.5' required along the BL. Original system lets > say calc'd 5 heads on the BL. But now in the same 46.5' there are 6 heads on > the BL. Do I ignore the wall and require a new calc? What if the wall is > rated 1 hour do I ignore it? > > I looked all over and can't seem to find anything definitive. Room design is > out so not a consideration. 22.4.4.1.1.1 simply says all the heads in the > 46.5'. I can't find anything that says either to count the wall as a break > so measure 46.5' from the wall in each direction and still see if there are 5 > head or ignore it and there are now 6 heads. I find 11.1.2 that clarifies to > extend the density or not. I don't think that's applicable exactly. The > question is not about whether to extend the density on either side. Let's > just say it's all OH. > > It gets a little more complex as on the one side of the wall they cut a head > in on the BL but on the other side there is a perpendicular new wall and they > come off same BL and arm over to two more head so if I ignore the walls there > are now 8 heads off the 1 BL. > > Prefer a code section or written reference 'cuz this is going to be a big > deal if we ignore the walls. Ordinarily with unrated walls they are ignored > in density/area (of course can't find that reference). I think I'm getting > tripped up with the rated portion? Or maybe I'm just tired???? > > Chris Cahill, PE* > Associate Fire Protection Engineer > Burns & McDonnell > Phone: 952.656.3652 > Fax: 952.229.2923 > [email protected]<mailto:[email protected]> > www.burnsmcd.com<http://www.burnsmcd.com/> > *Registered in: MN > > > Proud to be #14 on FORTUNE's 2014 List of 100 Best Companies to Work For > > > > > _______________________________________________ > Sprinklerforum mailing list > [email protected] > http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/listinfo.cgi/sprinklerforum-firesprinkler.org
