Notification Appliances and Signaling
This domain covers what occupants actually hear and see, and how signals reach the people who respond.
Audible requirements
In public mode the signal must exceed the average ambient by 15 dBA, or the maximum ambient lasting at least 60 seconds by 5 dBA, whichever is greater, measured in the occupiable space. Private mode, used in staff areas, calls for 10 dBA above normal ambient. Sleeping areas add a pillow-level requirement of 75 dBA. Upper limits also exist; where levels would endanger hearing, visible notification substitutes and the AHJ is consulted.
Visible appliances
Visible appliances are rated in candela, with standard sizes including 15, 30, 75, 110, 177, and 185. Required intensity rises with the square of the distance from the strobe to the farthest point, so a 30 ft dimension needs roughly 34 cd and a 75 cd appliance is the next listed size. Appliances flash once per second and must be synchronized when in the same field of view, and they mount 80 to 96 in. above the floor.
Signal priority
Alarm outranks supervisory, which outranks trouble. Emergency voice/alarm communication systems permit manual paging but must default to the evacuation message on failure. Where permitted, off-premises transmission to a supervising station handles notification of responding forces.
Worked example
A corridor beside machinery measures 60 dBA ambient, so the minimum is 75 dBA (ambient plus 15). A horn rated 85 dBA at 10 ft located at one end loses intensity along the corridor, so the designer verifies the level at the farthest occupiable point, not at the appliance face. If the far end falls short, add an appliance rather than raising the rating.
Traps
Applying private mode levels in public spaces; forgetting the pillow-level rule in sleeping rooms; confusing candela with loudness; missing synchronization in corridors where multiple strobes are visible together.