Notification Appliances: Audibility, Visibility, and Intelligibility
This domain tests the numbers behind occupant notification: sound pressure levels, candela selection, mounting heights, synchronization, and voice intelligibility.
Audibility
- Public mode: 15 dBA above the average ambient, with a minimum of 65 dBA.
- Private mode: 10 dBA above ambient, with a minimum of 45 dBA.
- Sleeping areas: 75 dBA at the pillow, or 15 dBA above ambient if that is higher.
- Sound levels must not exceed 110 dBA at minimum hearing distance.
- Low-frequency (520 Hz) appliances are required in sleeping areas because high-frequency horns are less effective at waking people.
Visibility
- Candela ratings are standardized (15, 30, 75, 110 cd) and coverage comes from the manufacturer's listed spacing tables for the mounting height.
- Wall-mounted visible appliances mount 80–96 in above finished floor.
- Visible appliances in the same field of view must be synchronized.
- Sleeping areas and high-ambient-light spaces need higher candela, up to 110 cd.
Voice intelligibility
Speakers must be both audible and understandable; designs commonly target STI or CIS of at least 0.45 and use the speaker's listed coverage pattern.
Worked example
A machine room measures 72 dBA average ambient. Public mode requires 72 + 15 = 87 dBA. A horn rated 90 dBA at 10 ft measures only 84 dBA at the far corner, so the design fails even though the nameplate number looks adequate. Corrective options: add appliances, use a higher-output model, or reduce the coverage area per appliance. Recheck that the result stays under 110 dBA near the appliance.
Traps that cost marks
- Applying the 65 dBA public-mode minimum without the +15 dB above ambient test.
- Using the appliance's 10 ft rating as if it were the level throughout the room.
- Mixing public and private mode criteria in the same occupancy.
- Omitting synchronization where two visible appliances are visible together.