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13. OPERATING PRINCIPLES OF SMOKE ALARMS
IONISATION CHAMBER:
A man-made radio-active element, Americium 241 is used in this design. This element
ionises the air round it and as a result, excellent conductivity is possible refer to illus-
tration showing ‘Clear Air’). Current supplied by either the mains power (where appli-
cable), or the battery would pass through the gap with ease without causing any alarm.
However, in the event of particles arising from combustion or dust particles (refer il-
lustration showing ‘Smoke’) entering the Sensing Chamber, it encapsulates the ionised
air. This interaction causes an increased resistance to conductivity. When this occurs,
the alarm is activated.
Ionisation type smoke alarm is best for detecting flaming fires.
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