| Primary value | 75 m² ((spot type, flat ceiling)) |
| Applies to | All occupancies with addressable / conventional smoke detection systems |
| Exceptions | Spot detector — flat ceiling → 75 m² per head |
| Beam smoke detector → Up to 1500 m² per pair | |
| Heat detector (rate-of-rise) → 40 m² per head | |
| Smoke detector, ceiling 9m to 11m high → 50 m² per head | |
| Heat detector, normal risk, up to 7m high → 50 m² per head | |
| Heat detector, high risk, up to 7m high → 25 m² per head | |
| Smoke detector in corridor <5m wide → Max 15m spacing between detectors | |
| Measured as | Plan area covered by one detector head, measured to the nearest wall or adjacent detector. |
| Source | NBC 2016 — IS 2189:1999, Table 2 (Smoke) & Table 1 (Heat). This standard is mandated by NBC 2016, Part 4, Annex E. ✓ Verified |
Correct spacing is critical for timely fire detection. If detectors are too far apart, a fire can grow significantly before smoke reaches a sensor, delaying alarms and evacuation. The 75 m² benchmark from IS 2189 is for flat ceilings up to 9m; this area must be reduced for higher or sloped ceilings, obstructions, or high airflow.
Designers lay out a grid ensuring no point on the ceiling is more than 7.5m from the nearest smoke detector. For large open areas like atria or warehouses, optical beam detectors are used. In spaces with high air velocity or fumes, like kitchens or generator rooms, heat detectors are specified to prevent false alarms.