Rate of rise detectors are designed to initiate a signal when the rise in temperature exceeds ____ to ____ degrees F within 1 minute.

• A. 8 to 10
• B. 12 to 15
• C. 20 to 25
• D. 30 to 35

Answer: (B)

Rate-of-rise detectors trigger not by how hot it is, but by how fast the temperature climbs at a location. They are set to alarm when the temperature increases faster than a certain amount per minute, here within one minute. The usual threshold for these detectors is about 12 to 15 degrees Fahrenheit per minute, so they will signal as soon as the temperature rise exceeds that range in a minute. This lets them catch a developing fire quickly even if the absolute temperature isn’t extremely high yet.

If the threshold were as low as 8–10 °F per minute, alarms could become nuisance alarms from normal heat fluctuations. If it were much higher, like 20–25 or 30–35 °F per minute, the detector might miss rapid fires that don’t have time to push temperature that high in a single minute. That’s why 12–15 °F per minute is the best balance.