"The designed system has little to do with physics or reality." Roland, I did not want to take your statement out of context completely, because I know how much that hurts sometimes, so I did not trim this thread.
I am always trying to quantify things as best I can so here is my shot: At the time calculations were being accepted into NFPA 13 the 'reality' was that pipe scheduled systems had worked for 90 years. In order for proposed changes to be accepted (then and now I guess) an equivalency of some sort had to be shown, and that is where the 'physics' came in, along these lines: given a certain water supply, what flows will a scheduled system produce? Now, for the sake of economy, how much can we beef it up here and slim it down there and still get equivalent results; mix a little fluid mechanics theory with a lot of water flow measurements and... BOOM! the density/area curves where born. So calculated systems using the density/area curves are nothing more than reconfigured pipe scheduled systems at their roots. This is just my current understanding, and if it is mostly correct, it makes real and perfect physical sense (to me anyway) ;) Brad Casterline, SET ps- I think calcs were a quantum leap in fire sprinkler design, and I think the future WILL involve 'fire having something to do with it'. -----Original Message----- From: Brad Casterline [mailto:[email protected]] Sent: Wednesday, May 21, 2014 12:12 PM To: 'Roland Huggins'; 'SprinklerFORUM' Subject: RE: Area/Density Method and Walls Three people took NFPA 13 from pipe scheduled to calculated: Jack Wood, Lin McCool, and Hasu Doshi. The Density/Area Curves "had nothing to do with fire" according to Hasu, the only one of the three still alive. The calculations were performed to see if they could get mains from 8" to 6" by making the lines a little bigger and still get the same total flow. So Chris, if you were pipe scheduling your set-up you would ignore the walls, right? So there is your answer. When I said I would consider any barrier I mean I would see in full color 3D the flames and smoke and sprinkler spray of what I think would probably happen, but what I would calc and print and walk the 40 feet to where my supervising FPE of ~35 years, Hasu Doshi, is, I will have ignored the walls. Hope that helps Cecil. Brad Casterline Designer Member, AFSA -----Original Message----- From: Roland Huggins [mailto:[email protected]] Sent: Wednesday, May 21, 2014 10:41 AM To: SprinklerFORUM Subject: Re: Area/Density Method and Walls 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 _______________________________________________ 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
