What is the primary characteristic Rate of Rise detectors monitor, and how fast must the rise be to trigger activation?

• A. Expansion characteristics of heat; activation at 12-15 degrees per minute.
• B. Expansion characteristics of heat; activation at 20 degrees per minute.
• C. Ambient humidity levels; activation at 12-15 degrees per minute.
• D. Air flow rate; activation at 12-15 degrees per minute.

Answer: (A)

Rate of Rise detectors respond to how quickly heat is increasing, using the expansion of a heat-sensitive element to sense a rapid temperature rise. They trigger when the temperature climbs at a rate of about 12–15 degrees per minute, rather than requiring a high absolute temperature. This makes them effective for detecting fast-developing fires where heat spikes occur quickly but may not reach a very high final temperature right away. Humidity and air flow aren’t what these detectors use to decide activation; those factors affect other sensor types, while the rate of rise is all about the speed of temperature increase.