Horizontal Combustible Concealed Space
“The concealed space sprinklers per 8.15.1.6 indicates that concealed spaces less than 3 ft shall be protected using listed sprinklers. We have an open wood truss construction that is tapered with the above portion being 5 ft and the lower being 2 ft. Concealed space sprinklers have specific requirements one of which is they are not listed in spaces greater than 3 ft. Q1) Should truss spaces be protected by standard spray sprinklers throughout? Q2) Should the space be protected by concealed space sprinklers throughout? Q3) Should the space be protected by a combination of standard spray and concealed space sprinklers? If so, which design strategy is applied (area/density or concealed space strategy?” We have reviewed NFPA 13, 2016 edition as the applicable standard. Our informal interpretation is that there are several approaches that can be used for this application. The wording in the standard may not be the best, but this section is requiring the use of sprinklers listed for applications for horizontal combustible concealed spaces less than 36 in. deep. As noted in the Handbook commentary, listed standard spray sprinklers were ineffective for fire control since the shallow space inhibits the discharge pattern development. When the space is greater than 36 in., standard spray sprinklers can be used. The sprinklers listed for horizontal combustible concealed spaces have better fire control since they provide a flatter pattern of spray. Additionally, the space must be horizontal (slope no greater than 2 in 12), the upper deck must be combustible, and there must be structural members that channel the heat (even as small as top chords on joists). A concealed space that does not contain all these conditions in NFPA 13 does not require the specifically listed sprinklers and as such, standard spray sprinklers can be used when steel pipe is used. There are listing requirements for CPVC piping located in protected horizontal concealed combustible spaces. The manufacturer of the plastic piping has additional requirements to follow. The manufacturer’s data sheet may indicate a minimum depth of 12 in. is needed in the concealed space to apply the specially listed sprinkler. Section 8.15.1.6.1 does allow the specially listed sprinklers to be used where the space is less than 12 in. from deck to deck in accordance with Section 8.3.1.2. The requirements of listings in Section 8.3.1.1 shall not apply where construction features or other special situations require unusual water distribution, and listed sprinklers shall be permitted to be installed in positions other than anticipated by their listing to achieve specific results. It is worth noting that 8.15.1.6 (and the sprinkler cut sheet) indicate these sprinklers shall only be used in spaces less than 36 in. The question does come up as what to do when the 2 in 12 slope with a long run creates a portion of the concealed space that is greater than 36 in. Section 8.15.1.6.2 indicates that sprinklers specifically listed to provide protection of combustible concealed spaces described in 8.15.1.6 shall be permitted to be used in accordance with 8.3.1.2 throughout the area when a portion of the area exceeds a depth of 36 in. As such, you have a choice to continue the concealed space sprinklers into spaces exceeding 36 in. On that note, Tyco has a CC3 sprinkler listed for horizontal concealed spaces up to 60 in. The other option is to transition to standard spray quick-response sprinklers when the space is greater than 36 in. Regarding the remote areas, there will be at least two different remote areas required. The minimum size of the remote area for standard spray sprinklers in this space would be 900 sq. ft. If there is insufficient area, the smaller actual size of the remote area can be applied, but additional water flow may have to be added as dictated by 23.4.4.2.4. Note there is an example on how this is applied in the annex. The other calculation would be the concealed space sprinklers having a minimum remote area size of 1,000 sq. ft. There is no guidance on how to address smaller remote areas that aren’t the entire compartment since the prior criteria apply only to the density/area method. There is no requirement to separate the two types of sprinklers. The exception is the draft curtains required by the manufacturer’s data sheets for the listed concealed space sprinklers. Refer to the sprinkler’s data sheets for the specifics on the draft curtains. It’s much cleaner if you simply use the listed sprinklers throughout the space. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.firesprinkler.org/private.cgi/sprinklernotes-firesprinkler.org/attachments/20170216/75eb32fd/attachment.htm>
