Notification Appliance Design — Audibility and Candela Ratings
Notification design has two independent jobs — be heard everywhere and be seen everywhere — each with its own set of rules.
Audible coverage
- Provide at least 15 dBA above average ambient, or 5 dBA above the maximum sound lasting 60 seconds, whichever is greater, throughout occupiable areas.
- Minimum 75 dBA at the pillow in sleeping rooms (with the door closed), using a 520 Hz low-frequency signal for new sleeping-area systems.
- Maximum 110 dBA at the minimum hearing distance.
Visible (strobe) coverage
Strobe candela (cd) is selected from tables by room size for a wall-mounted device on one wall:
| Square room | Min candela (1 strobe, centred wall) |
|---|---|
| 6.1 × 6.1 m | 15 cd |
| 9.1 × 9.1 m | 30 cd |
| 12.2 × 12.2 m | 60 cd |
| 15.2 × 15.2 m | 95 cd |
Large rooms use multiple strobes; corridors use spacing tables (e.g. 15 cd every 30 m, first within 4.6 m of the end).
Synchronization
Where more than two strobes are visible from any point, they must flash in synchronization (photosensitive-epilepsy safety). This needs sync modules or sync-capable circuits — a BOM and circuit-design item.
Load on the NAC
Total the current draw of all appliances on each Notification Appliance Circuit, add voltage-drop margin to the end of line, and confirm the panel/booster NAC rating covers it.
EngEst Pro’s FDAS Calculator selects strobe candela by room size, spaces horns and strobes to the audibility and visibility rules, totals the NAC load, and lists notification devices and circuit wiring in the BOM.
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