What is the purpose of bi-metallic heat detectors in fire alarm systems?

Bi-metallic heat detectors play a crucial role in fire alarm systems by detecting changes in heat levels. These devices are constructed from two different metals that expand at different rates when exposed to heat. As the temperature rises due to a fire or other heat source, the differing expansion rates cause the bi-metallic strip to bend. This bending activates a switch in the detection circuit, triggering the fire alarm.

This mechanism allows bi-metallic heat detectors to respond to significant increases in temperature, making them effective for identifying fire conditions before smoke or flames are visible. Their design ensures that they are reliable in situations where heat is the primary indicator of a potential fire hazard, effectively enhancing the overall safety of the environment they protect.

Understanding that the main focus of bi-metallic heat detectors is on temperature change clarifies why the other choices are not applicable. For instance, they do not detect smoke particles, control airflow, or measure humidity levels, which are functions associated with other types of sensors and systems.