6
Height
The maximum rec om mend ed installation height
is generally 25m (some local standards or codes
of practice might allow more under certain
circumstances) and the distance between the
beam and the ceiling should be within 0.3m
and 0.6m. No more than 3m of the beam path
(measured from the centre of the beam) should
be within 500mm of any wall or partitions.
If detectors are installed at a distance of more
than 600mm below ceiling level in order to
provide supplementary detection of smoke in a
building with a high ceiling, the installed height
of detectors should be in accordance with the
local code.
Pitched roofs and sloping ceilings
In buildings with pitched roofs or ceilings the
maximum distance either side of the beam in
the apex only may be increased by 1% for each
degree of ceiling pitch up to a maximum of 25%
(Fig 2).
Example: Roof pitch = 20°
Span of beam = 15m
15m + (15 x 20%) = 18m
There must be a clear line of sight between
the beam detector and refl ector at all times. If
there is any doubt about the correct mounting of
detectors in a particular installation, the position
may be de ter mined by smoke tests.
Refl ections from objects other than the prism
refl ectors may cause false alarms. Observe the
rules on minimum spacing as given on page 5. All
in stal la tions must conform to locally applicable
stand ards and codes of practice.
10˚
7.5m
7.5+8.25m
8.25+7.5m
20˚
18m max
7.5 + 7.5 + 3.m
Roof pitch = 20˚
Span of beam = 15m
15m + (15 x 20%) = 18m
Fig 2 Positioning detectors under different types of sloped or pitched roofs
