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Fire Side Chat THE HEAT DETECTION IS ON by Shane Clary Shane Clary, Ph.D., has more than 37 years of security and fre alarm industry experience. He serves on a number of NFPA technical committees, and is Vice President of Codes and Standards Compliance for Pacheco, Calif.-headquartered Bay Alarm Co. smclary@bayalarm.com T he rather blazing hot summer has gotten me thinking about heat detectors, or as they are referred to within NFPA 72, Te National Fire Alarm and Signaling Code, Heat-Sensing Fire Detectors. Heat detectors, in one form or another, have been around since the frst fre alarm standard was issued in the late 1800s. While smoke detectors are the primary method of automatic detection now installed as part of an automatic fre alarm system, the heat detector still has its uses and advantages over smokes in a number of applications. Smoke detectors provide early detection of an incipient fre and are listed as life-safety devices, but they cannot be installed in all locations or environments. Tis is especially true for dusty or dirty environments or those exposed to weather or moisture. Tere are several manufacturers that produce smoke detectors that can work within a number of harsh environments, but these may not be practicable for every application. Heat detectors should be considered when providing detection in environments that may be dirty, dusty, damp or wet, external, exposed to fog or mist. Tey may also be considered for those times when the installation of smoke detectors has caused unwanted alarms. One item of note is that heat detectors are not listed as life-safety devices, as they only detect a rise in heat, not the products of combustion. 48 / SECURITYSALES.COM / SEPTEMBER 2013 PHOTO: ©ISTOCKPHOTO.COM Though early fre detection is usually associated with smoke detectors, there are applications where a heat detector further enhances the preservation of property and life safety. Learn about the different types of heat detectors, and pick up some system design and installation pointers. 4 HEAT DETECTOR TYPES EXPLAINED Tere are four primary types of heat detectors on the market today: Fixed Temperature — Generally constructed using bimetallic components, this detector activates when a preset temperature is reached. Some models may also use eutectic solders. Te most common temperature settings are 130° and 190° F. When the temperature within the detector reaches the set parameter, it will go into an alarm state. If the sensor is bimetallic, once the detector fres it will have to be changed as this component cannot be used again. Note that this type of detector reacts not to the temperature outside but the internal temperature environment. Te diference between the external and internal temperature is called thermal lag. Rate-of-Rise — These are also constructed using bimetallic components, but may also be using thermistors. These detectors look for a sudden rise in temperature, generally 10° F during a one-minute time period. For example, the temperature of the environment may be 65° and rises to 80° within one minute. In this case, the rate-of-rise component of the detector would go off, but if the cause of the temperate increase was removed the detector would restore. Thermal lag comes into play with these detectors as well. The rate-of-rise detector also has