Heat detector

A heat detector is a device that detects heat. Heat detectors are often used as initiating devices on fire alarm systems.

Operation

Conventional Heat Detectors are often a mixture of fixed temperature and rate-of-rise. Fixed detectors work like pull stations. When they reach a certain temperature, a link in the device melts away, and a spring causes the short. Many fixed heat detectors cannot be re-used, and must be replaced if tripped. Some newer detectors use a thermistor which when cooled, allows the device to be reset.

Rate of Rise, however, will use power of the IDC to activate. When the temperature increases at a specific rate, the device will go into an active state. These can be reset and reused when they cool down.

Most common, modern conventional heat detectors are a combination of both fixed and rate of rise. If the rate of rise portion activates, it can be re-used. However, if the fixed portion activates, the device will need to be replaced.

Heat detectors in the intelligent sense are really just heat sensors. Upon a certain temperature, or rate of rise in temperature, the detector will let the panel know that things are getting warm, and the panel will activate.

Though this isn't what we are seeing in the industry yet, it is not far fetched that a heat detector might be able to be used in any application, and a setting be made in the panel for the temperature it activates, rather than the detector.

Open area protection

NFPA 72 section 17.6.3 includes requirements for heat detector placement when heat detectors are used to provide open area protection.

NFPA 101 requires heat detection in a few situations. Note that section 9.7.1.4 allows sprinklers to be used in place of heat detectors, and section 9.8.2.3 allows water mist systems to be used in place of heat detectors.

• Sections 14.3.4.2.3.1 and 15.3.4.2.3.1 allow pull stations to be omitted from educational occupancies under certain conditions, including the presence of heat detection or approved alternatives in all assembly areas and shops/laboratories.
• Section 31.3.4.4.2 requires existing apartment buildings utilizing "Option 2" to provide open area heat detection inside living areas.
• Section 32.2.3.5.7.2 includes alternatives that allow sprinklers to be omitted from attics of new residential board and care occupancies with 16 or fewer residents that would otherwise be required to have sprinklers, one of which is the presence of heat detection. Sections 33.2.3.5.7.2 and 33.3.3.5.4.2 include similar options for existing occupancies, without the size restriction, and allow heat alarms to be used as an alternative to heat detectors in small occupancies.

IBC/IFC also require open area heat detection in a few situations.

• Section 903.3.1.2.3 allows Group R-4 Condition 2 occupancies to omit sprinklers that would otherwise be required if one of several alternatives is provided, and one alternative is the presence of heat detection in the attic
• Section 907.2.3 allows pull stations to be omitted from educational occupancies under certain conditions, including the presence of heat detection or approved alternatives in all assembly areas and shops/laboratories.
• Section 907.4.3 requires heat detection in all areas that would otherwise require smoke detection but are unsuitable for smoke detectors. Note that for this specific requirement, sprinklers may be used as an alternative unless the detection system is required for a delayed/controlled egress lock or elevator recall.
• Section 1010.2.12 requires a sprinkler system, smoke detection system, or heat detection system in any building with delayed egress locks.

Other detector locations

Elevators

Heat detectors are often installed in elevator shafts and machine rooms for power shutdown before an adjacent sprinkler activates, if such sprinkler operation would be dangerous with a running elevator. Additionally, heat detectors are often used in place of smoke detectors for elevator recall when conditions are not suitable for smoke detectors.

Fire alarm system protection

NFPA 72 section 10.4.5 and IBC/IFC section 907.4.1 require a smoke detector to be installed above every FACP, power supply, and communicator located in an area not continuously occupied, but if ambient conditions are not suitable for a smoke detector, a heat detector is permitted to be used instead.