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18 E L EC TR I C AL CONNEC T I ON
SUMME R 20 1 6
WHERE THERE’S SMOKE...
I
onisation alarms were introduced in
1972 and now feature in about 90% of
Australian homes.
The trouble is, they were never
intended to be smoke detectors –
they are designed to detect flame.
By installing such a unit you could be
putting your customers’ lives at risk.
When photoelectric smoke detectors
entered the market they proved to be
a capable replacement for ionisation
alarms in homes. It seemed like an easy
path ahead for photoelectrics, but that
was not to be.
WHAT’S THE DIFFERENCE?
Ionisation and photoelectric smoke
alarms are designed to detect fire, but the
different technologies mean they detect
fires at different stages.
Ionisation alarms ‘smell’ the smoke
that comes from the flames of a fire.
The ionisation chamber is charged with
electrical particles, ions, by a small amount
of radioactive material.
Unlike the photoelectric model,
ionisation alarms are sensitive to small
particles of combustion that disrupt the
balance of ions, causing the alarm to
sound. This means they are marginally
better at detecting flaming fires that
produce smaller amounts of visible smoke.
Photoelectric units ‘see’ the smoke
before it bursts into flames. The chamber
has a light source projected into it, so
when visible smoke enters the chamber
it scatters and disturbs the light. The
alarm sounds once the large smouldering
fire particles are detected by the light-
sensitive receiver.
Both types are effective in detecting
most types of fire, but photoelectric
alarms are more advanced at detecting
smouldering fires, which are most often
associated with residential fatalities.
According to the Fire Protection
Association of Australia, this is because
smouldering fires are more likely to occur
while you are sleeping and won’t have
enough time to avoid the fire’s effects.
On the other hand, ionisation alarms
are marginally faster at detecting fast
flaming fires.
Flaming fires are still a threat, but they
are most likely to occur when residents
are alert – stoves or ovens are sources
of high heat, and gas cooktops introduce
naked flame.
It’s also important to note that ionisation
models are prone to false alarms, as the
technology can be set off by high humidity
from showers, harmless cooking steam
or smoke from burning toast. This is
important. A high incidence of false alarms
leads to occupant complacency and is an
incentive to disconnect the alarm.
THE IONISATION PROBLEM
It seems simple: photoelectric models
THERE ARE TWO KINDS OF
SMOKE DETECTOR ON THE
MARKET, BUT ONE OF THEM
DOESN’T DESERVE THE NAME.
PAUL SKELTON
REPORTS.
The heat is on for ionisation alarms as units fail to activate in the event of a fire.
COVER STORY