What triggers the thermal switch to activate in a fire detection system?

The thermal switch in a fire detection system is designed to activate based on the temperature reaching a predetermined threshold. This activation occurs when the surrounding environment heats to the specific temperature for which the thermal switch is calibrated. This makes option C the correct answer, as the proper functioning of the thermal switch relies on the detection of increased temperatures associated with potential fire conditions.

The operation of the thermal switch is based on thermal expansion or conductivity changes that occur when the set temperature is reached, triggering the system to signal a fire alert. This method is commonly employed because it provides a robust and reliable means of detecting heat that may indicate the presence of a fire.

Other factors like high humidity, circuit short-circuits, or power interruptions do not directly cause the thermal switch to activate. High humidity may affect the overall environment but does not trigger the heat-sensitive mechanism of the thermal switch. Circuit short-circuits are electrical failures that could result in different issues, but they are not related to the thermal activation of the switch. Similarly, power interruptions can affect the functionality of the detection system but do not play a role in directly triggering the thermal switch.