A rate of rise heat detector will respond when the temperature rises at a rate exceeding a predetermined amount, usually about ___ degree(s) per ___.

• A. 1, second
• B. 12-15, minute
• C. 8-10, minute
• D. 5, 15 seconds

Answer: (B)

Rate-of-rise detectors trigger based on how quickly the temperature climbs, not just the absolute temperature. They’re designed to react when the temperature rises rapidly, which is characteristic of a developing fire, while avoiding alarms from slow, normal ambient changes. The typical threshold used is about 12–15 degrees per minute, which translates to roughly 6.7–8.3 degrees Celsius per minute. This range provides fast detection without being overly sensitive to normal temperature fluctuations. That’s why the option of 12–15 degrees per minute is the best match. Rates that are much faster or slower—like 1 degree per second or 5 degrees every 15 seconds—don’t align with standard practice and would either cause nuisance alarms or miss a developing fire. An 8–10 degree-per-minute rate is plausible but not the commonly cited threshold, making 12–15 per minute the typical choice.