Bosch D296 Application Manual page 9

Projected-beam Smoke Detectors
Use normal spacing when the projected beams are running in the direction parallel to the run
of the beams or solid joists. Use half spacing when the projected beams are running at right
angles to the run of the beams or solid joists. A joist is a support that is 4 in. (100 mm) or
more in depth and 3 ft (0.9 m) or less in spacing . A beam is a support that is 4 in. (100 mm)
or more in depth and 3 ft (0.9 m) or more in spacing . See the following figure:
Figure 3.5: Flat Ceiling - Example A
Place the detectors in every ceiling beam pocket when the ceiling beams (joists) exceed 1 ft
(0.3 m), the spacing between the beams exceeds 8 ft (2.4 m), or the ceiling height exceeds
12 ft (3.6 m).
If you expect the fire size to exceed 1 MW (1000 kW), the ceiling height can be up to 28 ft
(8.5 m) before each beam pocket must be treated separately. Review Annex B‑2 Performance-
Based Approach to Designing and Analyzing Fire Detection Systems in NFPA 72 to determine the
potential fire size at the location. See the following figure:
Bosch Security System, Inc.
1 Transmitters (5)
2 Receivers (5)
3 Ceiling beams/joists (2)
S Selected detector spacing
Application Guide
Document Introduction | en
2013.02 | 02 | F.01U.500.951
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