Which detector responds to rapid changes in temperature?

• A. Rate of Rise
• B. Disk-Thermostat
• C. Infrared
• D. Bimetallic

Answer: (A)

Rate-of-rise detectors are built to sense how quickly the temperature is increasing, not just how hot it gets. In a fire, heat often climbs rapidly, and this type of detector trips when the rate of temperature rise exceeds its preset threshold, even if the final temperature hasn’t reached a fixed point yet. The sensing element, often a small sealed chamber or a thin bimetallic strip connected to a switch, responds to the rapid expansion or pressure change caused by quick heating and sounds the alarm.

Disk-thermostats and many fixed-temperature devices trigger when the temperature hits a specific value, so they may not react as quickly if the heat spikes are brief or don't reach the set point. Infrared detectors look for radiant heat from a heat source rather than the rate of temperature change, and standard bimetallic detectors typically respond to reaching a temperature threshold rather than the speed of rise. That focus on how fast the temperature climbs is what makes the rate-of-rise detector the best answer.