MAN3041-1
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7
Orbis IS Heat Detector
The Orbis IS range incorporates seven heat detector classes to suit
a wide variety of operating conditions in which smoke detectors
are unsuitable.
The European standard EN54-5:2000 classifies heat detectors
according to the highest ambient temperature in which they can
safely be used without risk of false alarm. The classes are identified
by the letters A to G. (Class A is subdivided into A1 and A2.) In
addition to the basic classification, detectors may be identified by a
suffix to show that they are rate-of-rise (suffix R) or fixed temperature (suffix S) types.
Item No
Part No
Description
201-0134
ORB-HT-51145-APO
Orbis I.S. A1R Heat Detector Rate of Rise
201-0135
ORB-HT-51157-APO
Orbis I.S. A1S Heat Detector Static
201-0601
ORB-HT-51147-APO
Orbis I.S. A2S Heat Detector Static
201-0600
ORB-HT-51149-APO
Orbis I.S. BR Heat Detector Rate of Rise
201-0607
ORB-HT-51151-APO
Orbis I.S. BS Heat Detector Static
201-0602
ORB-HT-51153-APO
Orbis I.S. CR Heat Detector Rate of Rise
201-0603
ORB-HT-51155-APO
Orbis I.S. CS Heat Detector Static
All heat detectors in the Orbis IS range are tested as static or rate-of-rise detectors and are classified as
A1R, A1S, A2S, BR, BS, CR and CS.
7.1
Where to use heat detectors:
Heat detectors are used in applications where smoke detectors are unsuitable. Smoke detectors are used
wherever possible since smoke detection provides earlier warning of fire than heat detection. There are,
however, limits to the application of smoke detectors and these are described in the section
4 ‘Choo
sing a
detector’
. Heat detectors may be used if there is a danger of nuisance alarms from smoke detectors.
7.2
Choosing the correct class of heat detector?
Heat detectors have a wide range of response characteristics and the choice of the right type for a
particular application may not always seem straightforward. It is helpful to understand the way that heat
detectors are classified as explained earlier and to memorise a simple rule: use the most sensitive heat
detector available consistent with avoiding false alarms.
In the case of heat detectors it may be necessary to take a heuristic approach, i.e. trial and error, until the
best solution for a particular site has been found. The flowchart in section 4 will assist in choosing the right
class of heat detector. If the fire detection system is being designed to comply with BS 5839
–
1: 2002 heat
detectors should be installed at heights of less than 12 metres with the exception of class A1 detectors,
which can be installed at heights up to 13.5 metres.
7.3
How does Orbis IS heat detectors work?
Orbis IS heat detectors have an open-web casing which allows air to flow freely across a thermistor which
measures the air temperature every 2 seconds. A microprocessor stores the temperatures and compares
them with pre-set values to determine whether a fixed upper limit
–
the alarm level
–
has been reached. In
