Note: BS 5446: Part 1 covers smoke alarms based on
ionization chamber smoke detectors and optical (photo-electric)
The different types of detector respond differently to smouldering
and fast flaming fires. Either type of detector is generally
However, the choice of detector type should, if possible,
take into account the type of fire that might be expected
and the need to avoid false alarms.
Optical detectors tend to be less affected by low levels of
invisible smoke that often cause false alarms.
BS 5839: Part 6 suggests that, in general,
optical smoke alarms should be installed in circulation
spaces such as hallways and landings, and
ionization chamber based smoke alarms may be the more
appropriate type in rooms, such as the living room or dining
room where a fast burning fire may present a greater danger
to occupants than a smouldering fire.