Hiya Chris, (we'll meet face to face some day, right?) NFPA 13 is a "prescriptive standard" (for those wondering: a standard that will cover just about any situation within certain parameters, so anyone can apply it). Which means we follow the rules as written. You are doing it right when you use the full 46.5' as the basis along a branchline that crosses rooms. Our trade is based, founded, and entrenched in the ability to apply these rules in this way. The rules are DEFINITELY too conservative for many situations. But that is what makes our prescriptive methods so successful. If it is enough for tough situations and too much for others, then we are sure to have the good record that we have created. To espouse a view, as has been suggested, that says to the vast majority of contractors and designers, "Do what feels good." is NOT an appropriate answer. The purpose of the remote area being 20% longer than the square (the square root for an inscribed circular fire...) is to make it more demanding on a single branchline and therefore a more conservative prescriptive system. (See the Academy's free remote area 101 lesson.) Chris, I know you to be a fair and firm professional. There is reason here to maintain and require consistency. (Give em an inch and.....) Stick with the definitions in the IBC/Minn and the NFPA and reality will be grand. It should be recognized that the above is my opinion as a member of the NFPA, and has not been processed as a formal interpretation in accordance with the NFPA Regulations Governing Committee Projects and should therefore not be considered, nor relied upon, as the official position of the the NFPA, nor any of their technical committees.
Sincerely, Cecil Bilbo Academy of Fire Sprinkler Technology Champaign, IL 217.607.0325 www.sprinkleracademy.com [email protected] OUR STUDENTS SAVE LIVES!! > From: [email protected] > To: [email protected] > Date: Tue, 20 May 2014 19:12:41 -0500 > Subject: Area/Density Method and Walls > > 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
