Detector Spacing Guide
Smoke and heat detector spacing, coverage areas, and mounting heights per BS 5839
Point Detector Coverage
BS 5839-1 specifies maximum coverage areas for point-type smoke and heat detectors based on ceiling height and detector type.
Maximum coverage per point detector (flat ceiling)
BS 5839-1, Table 4| Detector Type | Max Area (m²) | Max Radius (m) | Max Corridor Spacing (m) |
|---|---|---|---|
| Optical smoke | 100 | 7.5 | 15 |
| Heat (fixed temp) | 50 | 5.3 | 10.6 |
| Heat (rate of rise) | 50 | 5.3 | 10.6 |
| Multi-sensor | 100 | 7.5 | 15 |
Coverage assumes a flat ceiling up to 10.5 m height. Reduced coverage applies to higher ceilings.
Corridor Rule
Ceiling Height Effects
As ceiling height increases, detector coverage areas are reduced because smoke cools and disperses before reaching the detector.
Coverage adjustment for ceiling height
BS 5839-1, Table 4| Ceiling Height | Smoke Detector Area (m²) | Heat Detector Area (m²) |
|---|---|---|
| Up to 6 m | 100 | 50 |
| 6 m to 7.5 m | 90 | 40 |
| 7.5 m to 9 m | 80 | 30 |
| 9 m to 10.5 m | 80 | 30 |
| 10.5 m to 12 m | Not recommended | Not recommended |
For ceilings above 10.5 m, consider beam detectors or aspirating systems.
Beam Detectors and Aspirating Systems
Beam detectors project an infrared beam across a room to a reflector. They are suited to large open areas with high ceilings such as warehouses and sports halls. Each beam detector can cover up to 100 m beam length. The beam should be positioned between 500 mm and 600 mm below the ceiling to avoid the dead air layer.
Max beam length = 100 m, max lateral coverage = 15 m (7.5 m each side)- 100 m
- = Maximum beam path length
- 7.5 m
- = Maximum offset from beam to nearest wall
BS 5839-1, Section 22
Aspirating Detection
Positioning Rules
Mount detectors on the ceiling where possible. Maintain at least 500 mm from any wall, beam, or obstruction. Keep detectors away from air vents and HVAC diffusers — a minimum clearance of 1 m is recommended to prevent airflow from deflecting smoke away from the detector.
Pitched and Sloped Ceilings