FIRERAY PRODUCT GUIDE
Page 12
4.4.3 Stratification
Stratification occurs when smoke is heated by smouldering of burning materials and becomes less
dense than surrounding cooler air.
The smoke rises until there is no longer a difference between the smoke and the surrounding air.
Therefore, stratification may occur in areas where the air temperature may be elevated at the ceiling
level, but especially where there is a lack of ventilation.
On smooth ceilings, Optical Beam Smoke Detectors should generally be mounted 0.3 metres to 0.6
metres from the ceiling.
In many cases, however, the location and sensitivity of the detectors shall be the result of an
engineering evaluation that includes the following
Structural features
Size and shape of the room and bays
Occupancy and uses of the area
Ceiling height and shape
Surface and obstructions
Ventilation
Ambient environment
Burning characteristics of the combustible materials present
Configuration of the contents in the area protected
The results of an engineering evaluation may require an installation at a reduced height to defeat the
effects of stratification or other obstructions.
(A) This plume is narrow at the ground level and expands at higher levels; it can be detected readily
at these levels. (B) This fire is slow to develop; the temperature of the plume cools around 10 metres
to 15 Metres causing it to stratify at this level. (C) This plume develops at lower levels and doesn’t
cool until it reaches higher elevations. Due to the high temperature, its size is equal from floor to
ceiling.
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