What is the typical minimum activation temperature for ceiling-mounted snap-disk detectors?

• A. 90°F
• B. 100°F
• C. 110°F
• D. 120°F

Answer: (B)

Heat detectors with fixed temperature ratings trigger when ambient temperature reaches their set point. A ceiling-mounted snap-disk detector uses a disk that snaps open at a specific temperature, completing the circuit to raise an alarm. In typical applications, the lowest activation threshold used for these devices is 100°F. That rating strikes a balance: it avoids nuisance alarms in spaces that can get warm due to sunlight or heat sources, while still activating early enough to provide prompt warning for many fires.

Choosing a lower value, like 90°F, would lead to frequent false alarms in hot environments, while higher values, such as 110°F or 120°F, would delay detection until more extreme heat is present. So the standard minimum activation temperature for these ceiling-mounted snap-disk detectors is 100°F.