Ampac Orbis, Product Manual, Page: 5 / 22

3
MAN1509-4
ORBIS AUSTRALIAN PRODUCT GUIDE
4 Choosing a Detector: Questions and Answers
Question:
The Orbis range does not include an ionisation smoke detector. Are ionisation detectors redundant?
Answer:
Ionisation detectors have been used for many years as extremely reliable smoke detectors. They
have traditionally been recommended for use where the fire risk is likely to include very small-particle
smoke.
One reason why ionisation detectors have become less popular is that they are more sensitive to
phenomena that cause false alarms than optical detectors.
Question:
Any other reasons?
Answer:
Ionisation detectors use a tiny radioactive foil. Although they are entirely safe to use, ionisation
detectors are subject to strict regulations concerning transport, storage and disposal. Thus it is
becoming increasingly difficult to use ionisation detectors.
Question:
When would I use a MultiSensor?
Answer:
Multisensor smoke detectors have a heat sensing element which makes them more sensitive if a fire
develops heat as well as smoke. This speeds up the response of the detector in certain fires where
heat is generated rapidly, for instance in test fire TF5, which is an open, flaming liquid fire in which n-
heptane is burned.
Multisensor smoke detectors are recommended for open flaming fire risks.
If there is any doubt as to whether an optical detector or a MultiSensor smoke detector should be
used it is wise to fit a MultiSensor smoke detector.
Question:
Where would there be a need to install heat detectors?
Answer:
Heat detectors should be used if it is not possible to use smoke detectors. This will be the case
where normal industrial processes produce substances which could be mistaken for smoke by a
smoke detector, eg, flour mills, textile mills or loading bays with diesel engine vehicles.
The type of substance encountered here would cause frequent false alarms if smoke detectors were
fitted, so a heat detector is used instead.
Question:
How are heat detectors classified?
Answer:
AS7240 classifies heat detectors according to the ambient temperature in which they will be working
and ac
cording to whether they may be tested as ‘static’ detectors (changing to alarm at a preset
temperature) or ‘rate-of-rise’ (changing to alarm at a preset increase of temperature).
Heat detectors may also be marketed without either classification; but then the detection
characteristics are unknown.
All Orbis heat detectors are tested and classified as either static or rate-of-rise.