Notification Appliances and Circuits
What this domain covers
Audibility and visibility criteria, candela selection and mounting, synchronization, the evacuation signal pattern, and voice intelligibility.
Core rules
- Public mode audibility: 15 dBA above average ambient (or 5 dBA above maximum ambient, whichever is greater) and at least 65 dBA at 10 ft. Private mode: 10 dBA above ambient, 45 dBA minimum at 10 ft. Sleep mode: 75 dBA at the pillow.
- Standard fire evacuation signal is the three-pulse temporal pattern (T3); carbon monoxide uses four pulses (T4). Do not substitute one for the other.
- Visible appliances: 15 cd minimum in public mode; mount 80 to 96 in above the floor; coverage comes from the candela table - at a 10-ft ceiling, 15 cd covers roughly 20 ft × 20 ft, and required candela climbs as spacing increases.
- Synchronization: appliances visible from one another must flash in sync.
- Voice systems must be intelligible, not merely loud; design to a recognized intelligibility target and verify in the field.
- Candela drives current draw, so higher-candela devices can blow up a marginal voltage-drop calculation.
Worked example
A 40 ft × 30 ft conference room, 10-ft ceiling, measured ambient 50 dBA. Required level is 65 dBA (15 above ambient) at 10 ft. One horn rated 80 dBA at 10 ft yields about 74 dBA at 20 ft (6 dB loss per doubling of distance), so audibility is satisfied. For visibility, split the room into two 20 ft × 30 ft zones; check the candela table and mounting height, then confirm the NAC still meets voltage drop with the selected candela.
Traps that cost marks
Mounting visible appliances at 10 ft "for visibility"; forgetting restrooms, closets, and closed doors; skipping synchronization; mixing T3 and T4; verifying audible output in an empty, quiet building rather than at design ambient.