Fixed-temperature heat detectors vs rate-of-rise heat detectors: which best describes their operation and usage?

• A. Both types depend on sprinkler water flow.
• B. Fixed-temperature detectors trigger at a set ambient temperature; rate-of-rise detectors trigger on rapid temperature increase; use fixed-temperature in areas with steady heat gain, rate-of-rise where rapid heating or radiation sources exist.
• C. Fixed-temperature detectors only measure humidity.
• D. Fixed-temperature detectors are used only outdoors.

Answer: (B)

Fixed-temperature detectors and rate-of-rise detectors use two different ideas for sensing heat. A fixed-temperature detector trips when the surrounding air reaches a specific, preset temperature. It’s like waiting for the temperature to hit a fixed point, which makes it reliable in environments where heat loads are steady and predictable.

A rate-of-rise detector, on the other hand, looks at how fast the temperature is climbing. If the temperature shoots up quickly within a short time, the detector should alarm even if the absolute temperature isn’t very high yet. This is useful where there can be rapid heating or radiant heat sources that cause a quick temperature jump rather than a steady rise.

So, fixed-temperature detectors are ideal in areas with steady heat gain, while rate-of-rise detectors are better where there could be rapid heating or radiant heat sources.

The other statements aren’t accurate: heat detectors don’t rely on sprinkler water flow, fixed-temperature devices don’t measure humidity, and these detectors aren’t restricted to outdoor use.