I won't disagree with your statement of theory but we have a very long history of sprinkler success. The rules whether related to wetting the floor or plume dynamics are well tested. We simply don't have failures when complying with the code. The code says you don't have to space to this beam given compliance with the tables. Ok maybe there are 1 or 2 failures out there but I'll take that over 100+ years. And so what if the farther away heads go first. We calc 5 minimum and usually much more. Look at some of the testing in HPS. When ignition is between 4 sometimes all 4 don't even go off. We are aiming for control not suppression (except ESFR). In reality we actually achieve suppression a vast majority of the time.
If you want to up the stakes to suppression on the first head you sure could run CFD models but even they are not definitive. And what do we gain? And the cost of CFD modeling? And the manipulation of data and models and limitation of models for an agenda, can we say man induced global warming? We don't have enough people that can apply NFPA 13 properly now add CFD modeling? Now on to the legal matter of code enforcement, which is a criminal matter, if the legal enforcer i.e. fire marshal (vs. the generic AHJ that includes others like insurance) can't point to a section where you are not in compliance that's the end of the story. They can jump up and down and recite all the research in existence and even produce a CFD model showing failure. In the end if I've met the letter NFPA 13 I'm clear legally. True if there was ever a failure I might have a civil problem. NFPA 13 8.1.1 (3) is absolutely unenforceable in law. Now where is it defined what is satisfactory performance. We simple don't operate in a performance environment. Most likely never will. (5) implies IMHO the clearance requirements of the standard take into account satisfactory ability to control or suppress the fire. You have to have satisfactory activation to get satisfactory control. And everything in an annex is not enforceable either unless specifically adopted by the legal authority. Oh and welcome to the non-lurking club. It's a mix of friendly help, spirited discussion and the very rare argument. We can get a little friendly at times because some of us have been here for over 10 years. Many have met in person and some get together on a regular basis. While a certain person complained about the friendly nature on a professional forum we say BS it doesn't have to be all stuffy. About the only topic we avoid is the PE vs. tech debate and all PE's on the forum know when generic PE's are bashed it's those not here. Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. 763-658-4483 763-658-4921 fax Email: [email protected] Mail: P.O. Box 69 Waverly, MN 55390 Location: 4439 Hwy 12 SW Waverly, MN 55390 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Michael J. Ricks Sent: Thursday, February 11, 2010 8:04 AM To: [email protected] Subject: Beam obstruction rules It really depends on the location of the fire plume in relationship to the heads and where the jet will be directed by the roof/ceiling elements. When I said the AHJ "may" have a point. I was responding in the hypothetical. It the original post the second head would have been 10' away from the first beam and 19' away from the wall. Since fire plumes go straight up and then outward, if the fire were 11' feet away from the wall, two feet away from the first beam, chances are the first head located on the other side of the beam which is covering that part of the floor would not fuse. I assumed that there were more heads spaced along in the same beam pockets all spaced the same distance away from the wall. My guess is the row of heads 19 feet away from the wall and 8' away from the fire plume in the second beam pocket would all fuse before the head that is only six feet away. We also don't know what's past the second beam-since he said beam and not wall, what's happening past that point. I would need to see the plans to know what I really felt. My point is that just because you meet deflector distance (I do realize that his deflectors are less than 12" per the unobstructed rules) and obstruction rules, based on 8.1.1 and the fact that NFPA 13 doesn't address heads above the bottom of beams in unobstructed construction, your design may still be deficient when you look at the head layout in relation to fire sprinkler performance theory. As sprinkler designers, we often fall into the trap of thinking covering the floor area is what is most important. It is very important to look at our designs with regard to response time as well. Where will the heat go when there is a fire? Unfortunately, fires don't always start directly below our sprinkler heads. Unless there is a breeze in the building, the heat will go straight up and then outward from there. If there is nothing to cause it to collect it will follow the path of least resistance. It doesn't care if there is a sprinkler head 6 feet away on the other side of a beam. It might as well be a wall. Personally, I would ere on the side of caution and space to the beams in this case. Mike Ricks Katco Fire Sprinkler Design Interesting analysis and welcome to the jungle. However, if you read the handbook commentary it would seem that your concern about ceiling jets is addressed in the definitions of obstructed and unobstructed construction. I am far from an expert on the behavior of ceiling jets, but I would think in this situation as described, that the sprinklers as positioned, especially in a 17 ft span, would be within that jet. At 09:52 PM 2/10/2010, you wrote: >Not to be the contrarian here, this being my first post to this forum, but, >I believe the AHJ has a point. > > > >Given your beam spacing of over 7'-6" on center, you are dealing with >unobstructed construction here. NFPA 13 8.6.4.1.2, regarding placing the >deflector above the bottom of the structural member, relates to obstructed >construction. In obstructed construction, we are able to place deflectors >up to 22" below roof decks since the obstructions help collect heat to >assure prompt activation of the sprinkler head. (If you remember your older >versions of NFPA 13, we used to have to deal with the "panelized roof >limitations of 300 square feet to get the added deflector distance.) NFPA >13 doesn't specifically address the issue of placing the deflector above the >beam in unobstructed construction and although you are meeting the >obstruction requirements of 8.6.5.1.2, the issue here is response time. >8.1.1 (2) states "Sprinklers shall be positioned and located so as to >provide satisfactory performance with respect to activation time and >distribution." A8.1 also says "The installation requirements are specific >for the normal arrangement of structural members. There will be >arrangements of structural members not specifically detailed by the >requirements." Just because your head is not obstructed and you have met >the deflector distance requirements for unobstructed construction doesn't >mean it will work as intended. > > > >The theory behind automatic sprinkler performance requires that the head be >in the jet stream or in a pocket that will collect heat in a timely manner. >With limited obstructions to collect heat, that distance will be 5 to 12% of >the height of the ceiling above the fire source. This is the theory behind >the 12" deflector distance rule for unobstructed construction. Given the >language of NFPA A8.1 and 8.1.1 the AHJ is not off base in being concerned >with response times. Unless you have a 30'+ ceiling, I would have concerns >that the jet stream would be cut off by the beams and that the heat would >not collect fast enough to assure prompt activation of the head and/or >skipping would occur causing head outside of the fire area to activate prior >to heads in and around the fire area due to the jet stream being directed >away from those heads by the beams. > > > >Michael Ricks > >Katco Fire Sprinkler Design > >P.O. Box 607 > >555 South 100 East > >Salem, UT 84653 > >801-423-3096 Cell: 801-380-4651 > >mike at fire-sprinkler-design.com <http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum> > > > > > >_______________________________________________ >Sprinklerforum mailing list >Sprinklerforum at firesprinkler.org <http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum> >http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum > >For Technical Assistance, send an email to: support at firesprinkler.org <http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum> > >To Unsubscribe, send an email to:Sprinklerforum-request at firesprinkler.org <http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum> >(Put the word unsubscribe in the subject field) Todd G. Williams, PE Fire Protection Design/Consulting Stonington, Connecticut www.fpdc.com 860.535.2080 Michael Ricks Katco Fire Sprinkler Design P.O. Box 607 555 South 100 East Salem, UT 84653 801-423-3096 Cell: 801-380-4651 [email protected] _______________________________________________ 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)
