As a follow up, here is an informal interpretation from NFSA on this type of issue from the March 13th E-Tech Alert.
Question 3 - Beam and Girder Pocket Limitations for Obstructed Construction In NFPA 13 (annex section A.3.7.1(1) in the 2002 edition), the definition of beam and girder construction as a type of Obstructed Construction calls for "beams spaced 3 ft to 7-½ ft on center". However the definition does not provide a maximum square footage for the beam and girder pocket. We have a building that has steel I-beams spaced 7'-6" apart but these beams sit on larger trusses, thus creating an air gap above the two ends above the truss. This being said, can we consider this Obstructed Construction? Answer: Yes. As described, the trusses are perpendicular to the beams and provide their support. If the tops of the beams are at the ceiling and the trusses are below then the beams should be considered the primary ceiling structure. The sprinklers' ability to collect heat and distribute a spray pattern is going to be affected most by the structural members directly below the ceiling. As you have noted, beam type construction spaced 3 to 7.5 feet on center is obstructed construction. There is no requirement that the beams frame into the trusses or that a maximum size of pocket be provided. The location of the trusses with regard to sprinkler spacing must be considered so that they do not create obstructions to sprinkler discharge patterns. In older editions of NFPA 13, beams that framed into other beams to form pockets less than 300 sq. ft. were given special consideration as "panel construction". Sprinklers were permitted to be placed further below the ceiling due to the greater capacity of panel construction to bank heat. While this type of construction is still defined in annex section A.3.7.1(4), there is no allowance for greater sprinkler deflector distances below the ceiling. This annex section can be used, however, to justify obstructed construct ion deflector distances even where members are spaced more than 7.5 ft on center provided the ceiling pocket criteria is met. This can be useful in situations where there are multiple adjacent ceiling pockets. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ray Vance Sent: Thursday, October 18, 2007 3:50 PM To: [email protected] Subject: RE: purlins To All: The proper definition, in my humble opinion is still beam and girder construction, therefore obstructed contruction. Girder, by definition, is "a strong horizontal beam used as a main support inside a building" ie, the support beam system (girder) on which the purlins sit. There are no length nor volume limitations imposed by NFPA on this type of construction, nor does it classify any type of "panel" configuration be maintained. The determining factor is that the SPACING between the purlins "framed into or on" the girder must be between 3 ft to 7 1/2 ft on center. If the beam/purlin spacing exceeds 7 1/2 ft on center, then you can still classify it as PANEL construction, provided the 300 sq.ft. "panel" limitation is met. With typical purlin depths of 8" to 10", the following scenarios tend to play out: (1) If you classify it as unobstructed, your deflector distance will be 1" to 12" below the deck or insulation (with standard spray sprinklers). (2) If the purlins are 12" in depth, you can still install the sprinklers with the deflectors even with the bottom of the purlin and meet the deflector and obstruction rules. (3) If you classify it as obstructed, your deflector will be 1" to 6" below the purlins not to exceed 22" below the deck or insulation. (4) Or you can install the sprinklers with the deflector even with the bottom of the purlins and meet the deflector and obstruction rules. (5) If ESFR sprinklers are considered, then your main concern is if the purlins are more than 12" deep, you must install ESFR's in every bay formed by the purlins. As to the "open space" formed by the purlins sitting on the girder, the volume of opening created at each end of the span will not typically create a large enough concern to warrant a change in the construction definiton, in my opinion. I would think that NFPA would have given direction on this if it was of a major concern. Thanks, Ray Vance Chief Engineering Tech. Wayne Automatic Fire Sprinklers, Inc. www.waynefire.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Greg McGahan Sent: Thursday, October 18, 2007 3:07 PM To: [email protected] Subject: RE: purlins Based on what? It clearly does not fall into panel construction due to the space above the beam. They are not girders. I am not fighting for or against, I just would like a conclusive answer. Is there not a manufacturer or committee member there that could enlighten us? I would think that the tests run on these storage heads and such would have forced a definition for the manufacturers. Greg Living Water Fire Protection, LLC 1160 McKenzie Road Cantonment, FL 32533 850-937-1850 Fax: 850-937-1852 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Todd Williams - FPDC Sent: Thursday, October 18, 2007 1:59 PM To: [email protected] Subject: RE: purlins Up here, it usually goes beams, purlins above (on) the beams, steel deck on the purlins. The insulation goes in between the purlins. Is the insulation going on the metal deck roof?If the insulation comes to the bottom of the purlin, it will create a fairly flat ceiling and I would consider it unobstructed. If there is no insulation, I would think it would be considered obstructed. At 02:51 PM 10/18/2007, you wrote: >No, above them. A typical warehouse. > >Living Water Fire Protection, LLC >1160 McKenzie Road >Cantonment, FL 32533 >850-937-1850 >Fax: 850-937-1852 > > >-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Todd Williams >- FPDC >Sent: Thursday, October 18, 2007 1:50 PM >To: [email protected] >Subject: Re: purlins > >Is there insulation between the purlins? > > >At 02:45 PM 10/18/2007, you wrote: > >Poll: > > > >Are typical 8" and 10" purlins spaced 4-5' apart with open space > >above the beams where the purlins rest considered OBstructed or > >Unobstructed construction? > > > > > > > >Living Water Fire Protection, LLC > > > >1160 McKenzie Road > > > >Cantonment, FL 32533 > > > >850-937-1850 > > > >Fax: 850-937-1852 > > > > > > > >_______________________________________________ > >Sprinklerforum mailing list > >[email protected] > >http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum > > > >To Unsubscribe, send an email > >to:[EMAIL PROTECTED] > >(Put the word unsubscribe in the subject field) > >Todd G. Williams, PE >Fire Protection Design/Consulting >Stonington, Connecticut >www.fpdc.com >860.535.2080 >_______________________________________________ >Sprinklerforum mailing list >[email protected] >http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum > >To Unsubscribe, send an email >to:[EMAIL PROTECTED] >(Put the word unsubscribe in the subject field) > >_______________________________________________ >Sprinklerforum mailing list >[email protected] >http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum > >To Unsubscribe, send an email >to:[EMAIL PROTECTED] >(Put the word unsubscribe in the subject field) Todd G. Williams, PE Fire Protection Design/Consulting Stonington, Connecticut www.fpdc.com 860.535.2080 _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list [email protected] http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum To Unsubscribe, send an email to:[EMAIL PROTECTED] (Put the word unsubscribe in the subject field) Wayne Automatic Fire Sprinklers, Inc. 2006 Inductee into "The Players Hall of Fame" at The Great Games of Business Wayne Automatic Fire Sprinklers, Inc. 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