NFPA 72 National Fire Alarm Code
A.5.7.5.2 For the most effective detection of fire in high-rack storage areas, detectors should be located on the ceiling above each aisle and at intermediate levels in the racks. This is necessary to detect smoke that is trapped in the racks at an early stage of fire development when insufficient thermal energy is released to carry the smoke to the ceiling. Earliest detection of smoke is achieved by locating the intermediate level detectors adjacent to alternate pallet sections as shown in Figure A.5.7.5.2(a) and FigureA. 5.7.5.2(b). The detector manufacturer’s recommendations and engineering judgment should be followed for specific installations.
A projected beam–type detector can be permitted to be used in lieu of a single row of individual spot-type smoke detectors. Sampling ports of an air sampling–type detector can be permitted to be located above each aisle to provide coverage that is equivalent to the location of spot-type detectors. The manufacturer’s recommendations and engineering judgment should be followed for the specific installation.