A rate-of-rise heat detector will signal an alarm only when the temperature in the monitored area reaches a predetermined threshold.

• A. True
• B. False
• C. Depends on installation
• D. Only during power failure

Answer: (B)

Rate-of-rise detectors trigger based on how quickly the temperature climbs, not on hitting a specific temperature. They monitor the change in temperature over a short interval and alarm when that rate exceeds a preset value. This means an alarm can occur even if the absolute temperature hasn’t reached any fixed threshold, as long as the rise is rapid enough. Conversely, a slow temperature increase to a high level might not trigger if the rate stays below the preset limit. Some detectors may include a separate fixed-temperature element to reduce false alarms, but the defining behavior is rate-of-change, not an absolute temperature. So the statement is false.