Vortex
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Mounting of oxygen detectors requires knowledge of the gas displacing the oxygen.
For example, carbon dioxide is heavier than air and displaces oxygen at a low height.
Under these circumstances oxygen detectors should be placed near ground level.
When locating detectors, consider the possible damage caused by natural events such
as rain or flooding. For detectors mounted outdoors, Crowcon recommends the use of
weatherproof caps or spray deflectors.
Consider ease of access for functional testing and servicing.
Consider how the escaping gas may behave due to natural or forced air currents.
Mount detectors in ventilation ducts if appropriate.
FIELD DEVICES
Consider the process conditions. Gases that are normally heavier than air, but are
released from a process line that is at a high temperature and/or under pressure, may
rise rather than fall.
The placement of the sensors should be decided following the advice of experts with
specialist knowledge of gas dispersion, experts with knowledge of the process plant
system and equipment involved, and safety and engineering personnel. The agreement
reached on the locations of sensors should be recorded.
5.3 Fire detectors
Only one fire loop may be fitted to each Quad Channel Input Module, and this can only be
connected to the first input channel. Up to 20 detectors, for example, Apollo Series 65 or
Orbis, may be used on the same loop at any time. The fire loop can also support other
switched devices such as manual call points.
Devices on the loop may be mixed provided electrical characteristics are compatible and fire
regulations allow.
All fire loops require a 1.8Kohm end-of-line resistor to be fitted (Rt in Figure 13). Simple
switch devices such as manual call points require a 470ohm series resistor (Rm.in Figure 13).
A fire detector circuit can be represented by an equivalent circuit of a switch operating in
series with a sensor resistor (Rs in Figure 13).
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