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Fire Side Chat PHOTO: @ISTOCKPHOTO.COM a fixed-temperature with their Response Time component. Index. RTI was added back to the requirements for Rate Compensation — heat detectors in the 2010 Tese detectors address edition. When originally thermal lag, and will trip included in NFPA 72, it when the external temcame from the requireperature reaches the rated ments for sprinklers. Te limit. Tis detector will acmethod for calculating RTI tivate quicker than a f xed for sprinklers, however, or rate-of-rise device. would not work for a heat Line Type — Te three detector. Researchers at detectors discussed above FM Global developed a are referred to as spot-type method for the calculation detectors, in which the Heat detectors, which can be deployed in cooking areas, are not listed as of RTI for heat detectors device is located in a f xed life-safety devices, as they detect a rise in heat rather than the products of and it was then placed position and will respond combustion. back in 72. RTI provides a to temperate increases method to measure the speed of a detector's response. within the listed spacing. In most cases, this is within a circular pattern, with the detector being in the center. Linear 17.6.2.3 Detectors having fxed-temperature or rate-comdetectors typically follow a cable that is installed throughout pensated elements shall be selected in accordance with Table the protected property or space. Te coverage is based from 17.6.2.1 for the maximum expected ambient ceiling temperathe position of the cable outward. Tis type of detector may ture. Te temperature rating of the detector shall be at least be installed in difcult-to-reach or -cover spaces within an 20° F (11° C) above the maximum expected temperature at the occupancy. Depending on the type being used, the cable ceiling. may be zoned so as to provide a location from which the Tis is a section that is overlooked during the design and alarm trip originated. installation of heat detectors. If installing detectors within an attic space or other area that may be subject to high heat, the detector cannot be listed for a temperature that is less DESIGN AND INSTALLATION GUIDELINES than 20° F higher than the expected maximum temperature. Te installation and spacing of heat detectors is found in For example, you would not install a 130° f xed temperature Section 17.6 of NFPA 72, 2013 edition. Tere are a number of detector in a space that may exceed 110° or 120° during the requirements the system designer and installer need to be summer. Nor would there be any cases to install a rate-ofaware of when heat detectors are used. Te following are key rise in an attic space. excerpts from Section 17.6 followed by my comments: 17.6.3.1.3.1 Unless otherwise modifed by 17.6.3.2.2, 17.6.3.3.2 or 17.6.3.7, spot-type heat-sensing fre detectors shall be 17.6.1.1 Te heat detection design documentation shall state the required performance objective of the system. Te designer located on the ceiling not less than 4 inches (100mm) from the sidewall or on the sidewalls between 4 inches and 12 inches of the system must provide a brief statement as to the ex(100-300mm) from the ceiling. pected design performance of the heat detectors that are to Tis rule has not changed in a number of editions. Do not be installed. confuse the requirements for heat detectors with smoke 17.6.2.2.2.3 Spot-type heat detectors shall also be marked detectors. Te exclusion of the 4 inches has been removed for smoke detectors, but not heat detectors. DETECTOR APPLICATIONS 17.6.3.1.3.2 Unless otherwise modifed by 17.6.3.2.2, 17.6.3.3.2 or 17.6.3.7, line-type heat detectors shall be located on the ceil• Elevator shunt trip ing or on the sidewalls not more than 20 inches (510mm) from • Shower rooms the ceiling. • Wet janitor closets Line-type or linear detectors may be installed on a side • Attics wall, but they must be at least 20 inches from the ceiling. • Warehouses, depending on the environment Spacing between links would be in accordance with the • External building areas manufacturer's published instructions and NFPA 72. • Mechanical spaces • Cooking areas • Industrial spaces • Areas of high heat 50 / SECURITYSALES.COM / SEPTEMBER 2013 I will discuss and hopefully demystify the requirements for the spacing of heat detectors in next month's column.