Heat detector

Heat detector

A heat detector is a device that responds to changes in ambient temperature. Typically, if the ambient temperature rises above a predetermined threshold an alarm signal is triggered. In the case of sprinkler systems, water will be released to extinguish the fire.

Heat detectors can also be further broken down into two main classifications of activation, "rate-of-rise" and "fixed." The most sophisticated units are activated by both conditions.

Rate-of-rise heat detectors

Rate-of-rise (ROR) heat detectors react to the sudden change or rise in ambient temperature from a normal baseline condition. Any sudden temperature increase that matches the predetermined alarm criteria will cause an alarm. This type of heat detector can react to a lower threshold condition than would be possible if the threshold were fixed. A typical alarm may sound when the rate of temperature rise exceeds 12° to 15°F (6.7° to 8.3°C) per minute.

Fixed temperature heat detectors

This type of detector reacts when the ambient temperature reaches a fixed point. The most common fixed temperature point is 136.4°F (58°C). Recent technological developments have enabled the perfection of detectors that activate at a temperature of 117°F (47°C), providing increased time to escape.

Heat detector selection

Heat detectors are not meant to replace smoke detectors in the bedrooms or in the hallway outside of the bedrooms. A heat detector will nonetheless notify of a fire in a kitchen or utility area (i.e., laundry room, garage, or attic), where smoke detectors should not be installed. This will allow extra time to evacuate the building or to put out the fire if possible.

Mechanical heat detectors are independent fire warning stations that - unlike smoke detectors - can be installed in any area of a home. Portability, ease of installation, and excellent performance and reliability make this a good choice for residential fire protection when combined with the required smoke detectors. Because the detectors are not interconnected, heat activation identifies the location of the fire, facilitating evacuation from the home.

Each type of heat detector has its advantages, and it cannot be said that one type of heat detector should always be used instead of another. If you were to place a rate-of-rise heat detector above a large, closed oven, then every time the door is opened a nuisance alarm could be generated due to the sudden heat transient. In this circumstance the fixed threshold detector would probably be best. If a room filled with highly combustible materials is protected with a fixed heat detector then a fast-flaming fire could exceed the alarm threshold due to thermal lag. In that case the rate-of-rise heat detector may be preferred.

ee also

* Fire alarm
* Flame detector
* Aspirated smoke detector
* Carbon monoxide detector
* Manual call point or Break glass alarm
* Fire sprinkler
* Gaseous fire suppression
* Automatic fire suppression


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