Heat detectors operate on one of two principles. Which are they?

• A. Fixed Temperature
• B. Rate of Rise
• C. Fixed Temperature and Rate of Rise
• D. Humidity Sensing

Answer: (C)

Heat detectors rely on two sensing strategies. One uses a fixed temperature threshold: when the ambient temperature reaches the preset point, the detector trips. This is straightforward and reliable in steady conditions, but it can be slow if the fire heats the area gradually. The other is rate-of-rise: if the temperature increases rapidly, the detector triggers even if the overall temperature isn’t very high yet. This catches fast-moving fires earlier in spaces where the heat buildup is quick. Some detectors combine both methods in a single unit to improve reliability. Humidity sensing isn’t part of heat detection; it’s a different monitoring approach altogether. So heat detectors operate on fixed temperature and rate of rise.