October 17, 2016
Remote Area for Unprotected Concealed Combustible Space “We have an NFPA 13 system that contains combustible concealed spaces formed by solid wood joists. Some of the spaces have been protected as a light hazard occupancy using upright, extend coverage sprinklers. Some of the concealed spaces have a ceiling attached to the joists and meets the allowance in 8.15.1.2.5. Since this is an allowed omission of protection, am I required to apply the requirement for a 3,000 sq. ft. remote area by 11.2.3.1.5? If applied, must all the allowances be applied concurrently, how is the 3,000 sq. ft. applied in conjunction with other modifiers, and what density applies to the design basis?” We have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is below. Allow me to start with the bad news. An extended coverage sprinkler cannot be used with combustible, obstructed construction as dictated by 8.4.3. Generally speaking, extended coverage can be used only with smooth ceilings unless listed otherwise and that’s limited to noncombustible, obstructed construction. There is an allowance in 8.4.3(6) for their use when installed in every bay that is then treated as a smooth ceiling between the structural members. As for the concealed spaces, all combustible concealed spaces must be protected unless they meet one of the 15 allowances identified in 8.15.1. When a concealed space is allowed to be unprotected, you then have to go to section 11.2.3.1.5 to determine whether you have to increase the size of the remote to 3,000 sq. ft. for the system adjacent to the unprotected concealed space. There are 10 allowances whereby the larger area does not apply. Allow me to emphasize that applying the 3,000 sq. ft. remote area does not allow omission for spaces not identified in 8.15.1. So returning to your particular case, 8.15.1.2.5 allows spaces with ceilings within 6 inches of wood joists to be unprotected. Another nuance is that this application of wood joists does not include composite wood joists as discussed in A.3.7.1(3) and (6). The two are treated as individual types of structural members due to how quickly the web burns through on the composite wood joists. Going to Chapter 11, you also are not required to increase the size of the remote area since 11.2.3.1.5.2(4) addresses this assembly. This section has been complicated by combining two situations into one allowance but focus on the specific statement on the ceiling attached directly to the bottom of the solid wood joist. I assume the volume of the channel is less than 160 cu. ft. (which is not a requirement for omission of protection). Also note the increased area would apply if the ceiling were up to 6 inches below the joists as allowed by 8.15.1.2.5. Although worded awkwardly, saying “unless the requirements of 11.2.3.1.5.2 are met” does not mean that all of them are applied concurrently but that any one of them applies. Otherwise, it would say must comply with all of the requirements. Additionally, if the 3,000 sq. ft. remote area is applied, it is the final area after all modifiers are applied as stated in 11.2.3.2.7.2. There is also no specified density but simply a minimum size. For instance, for a light hazard occupancy classification with no modifiers, you can apply a density of 0.07 gpm/ sq. ft. over 3,000 sq. ft. in accordance with Figure 11.2.3.1.1. ------------ Technical Update is prepared by the Technical Services Dept. of the AFSA: Roland Huggins, a PE registered in fire protection engineering, Vice President of Engineering and Technical Services; and Tom Wellen, a PE registered in fire protection engineering. This is provided with the understanding that the AFSA assumes no liability for this opinion or actions taken on it and they are not to be considered the official position of the NFPA or its technical committees. Copyright 2016, American Fire Sprinkler Association. All Rights Reserved. Ada Dickson Ada Dickson Administrative Assistant Technical Services Dept. PH: (214) 349-5965 ext. 124 Fax: (214) 343-8898 E-mail: [email protected] -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.firesprinkler.org/private.cgi/sprinklernotes-firesprinkler.org/attachments/20161017/2a43bb4b/attachment.htm>
