Smoke Alarm User Manual

14
Note: This document is based on the recommendations of BS5839 Part 1: 2002. It is intended only as a guide to the application of fire detection systems.
Reference must be made to relevant national and local standards.
Application Guide
Figure 2.4.3: Detector Spacing around isolated ceiling
obstructions
2.4.4. Partitions and Racking
Where the gap between the top of a partition or section of
racking and the ceiling is greater than 300mm, it may be
ignored. If the gap is less than 300mm it should be treated as
a wall.
To maintain a free flow of smoke and heat to the detector, a
clear space should be maintained for 500mm in all directions
below the detector.
Figure 2.4.4. Partitions
2.4.5. Sloping Ceilings
Where the ceiling is pitched or sloping, the slope of the
roof tends to speed the rise of smoke or heat to the apex,
hence reducing the delay before the detectors are triggered.
For sloped roofs with a pitch height greater than 600mm
for smoke detectors, or 150mm for heat detectors, a row
of detectors should be placed within a maximum vertical
distance of 600mm or 150mm for smoke or heat detectors
respectively from the roof apex. Sloped roofs rising less than
600mm for smoke detectors or 150mm for heat detectors may
be treated as a flat ceiling.
Since the smoke or heat tends to rise faster up the slope, it is
permissible to use a greater spacing for the row of detectors
mounted in the apex of the roof: For each degree of slope
of the roof, the spacing may be increased by 1% up to a
maximum of 25%. Where, as in figure 2.4.5, the roof slopes
are unequal the spacing down the slopes can be unequal,
however along the roof apex spacing the lesser of the two
figures should be used, in this example 10.5m +18%. Where
the slope finishes within the adjusted detection radius, the
standard distance to the next row of detectors, 10.5m, should
be used. Care must be taken when placing the next row that
no gaps are left in detection coverage.
Figure 2.4.5. Spacing of Smoke Detectors under a
Pitched Roof
2.4.6. Corridors
In corridors less than 2m wide, detectors should be spaced
at a distance of 15m for smoke detectors and 10.6m for heat
detectors, with the maximum dimension to a wall at the end of
the corridor being 7.5m and 5.3m respectively.
In narrow rooms and corridors greater than 2m wide, due to
the way that the coverage radii of detectors intersect with
the walls of the corridor, the spacing between detectors
will increase. Figure 2.4.6 shows how, for a room 6m wide,
the spacing for smoke detectors can be increased from the
standard 10.5m.
Figure 2.4.6. Smoke detector spacing in corridors greater
than 2m wide
>300mm : No effect
<300mm :Treat as wall
Minimum
500mm
Clear
Pa
r
tition
Racking /
Shelving
18°
15m
Max 600mm
10.5m
12.39m
=10.5 + 18%
7.5m
8.85m
=7.5 + 18%
9.35m
= 7.5 + 25%
40°
Minimum
500mm
Minimum
500mm
Minimum 2
x
height
>250mm
<10% of Ceiling Height
>10% of Ceiling Height
Height < 250mm
Normal Detector Spacing, eg. 10.5m max
fo
r “simple” layout.
Normal Detector Spacing, eg. 10.5m max
fo
r “simple” layout.
Treat as separate room
Note: Detectors are mounted in the centre line of the room
6.88m 13.75m
7.5m
6m