Notification Appliances and Audibility/Visibility Requirements
Audibility
The evacuation signal must be distinctive and unmistakable. In public mode the sound level must be at least 15 dBA above the average ambient level, or 5 dBA above the maximum ambient lasting more than 60 seconds, whichever is greater, and never below 65 dBA. In sleeping areas the target is 75 dBA at the pillow, or 15 dBA above average ambient if that is higher. Private mode uses a lower threshold (45 dBA). Measurements are taken at the occupied level, commonly about 5 ft above the floor, not at the appliance.
The evacuation signal
The standard fire evacuation tone is temporal-three: three 0.5-second pulses separated by 0.5-second gaps, followed by a 1.5-second pause, repeated. Voice systems must deliver intelligible speech, not just loud noise.
Visibility
Visible appliances are rated in candela and spaced by rating and mounting height: on a smooth ceiling, 15 cd covers about 20 ft, 30 cd about 25 ft, and 75 cd about 30 ft in a corridor. Sleeping areas need substantially higher candela for the same distance. Appliances mount 80 to 96 in. above finished floor, and visible notification must be synchronized when multiple appliances are visible in the same area.
Worked example
A machine room measures 62 dBA ambient, with occasional peaks of 68 dBA lasting over a minute. Fifteen above 62 is 77; five above 68 is 73; the 65 dBA floor is not controlling. The design target is 77 dBA at the occupied level, so an appliance specified at 75 dBA fails.
Traps that cost marks
- Measuring at the appliance or at 10 ft instead of the occupied location.
- Forgetting the 75 dBA pillow requirement in sleeping rooms.
- Using 15 cd everywhere and ignoring ceiling height and distance.
- Mixing ambient average with ambient maximum when selecting the greater value.