Please advise on the maximum permissible working heights for Smoke detector, Heat detector and combined smoke/heat detector as per NFPA-72.
The quick review for your question.
Smoke detector location and spacing shall be based on anticipated smoke flows due to the plume andceiling jet produced by an anticipated fire, which should take into account: 1) ceiling shape and surface,2) ceiling height, 3) configuration of contents, 4) combustion characteristics of fuel load, 5) compartmentventilation, 6) ambient pressure, pressure, altitude, and humidity. Provide document attesting that theseitems were applied, 18.104.22.168.2 AHJ may require supporting documentation.
Smoke detector spacing for smooth ceiling will use 30 ft. spacing as a guide, manufacturer’s data sheetlisting criteria shall be followed. Other spacing is permitted depending on ceiling height, etc., fordetecting flaming fires the guidelines of Annex B can be used, all points of a ceiling are within .7 (70%)of the selected spacing, 22.214.171.124.3.
If the spot smoke detectors are located above the ceiling height of the table projected beam detectors may be used. The detection system should then be engineered. Projected beam smoke detectors: stratification for a high ceiling was considered in the beam detector’s use and documentation is provided attesting that this evaluation was done, 126.96.36.199.2.
Heat detector spacing for ceilings 10 ft. to 30 ft. shall be reduced in accordance with NFPA 72 Table 188.8.131.52.1.prior to reductions for sloped, joist, or beam construction and not less than .4 (40%) of the height of theceiling, alternate designs can be in accordance with Annex B, 184.108.40.206.1.
If you use combination smoke/heat detector the most restrictive requirements of the heat or the smoke detection must be followed.
Thank you very much for your detailed response, it is very useful. May I know the edition year of NFPA-72 you are referring to please?
The references should be from the 2007 NFPA 72.
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