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11
3.
INSTALLATION
3.1.
Location
Gas detectors must be placed so that potential gas accumulations are detected before they create
a significant hazard. Inappropriate location of a detector can nullify the effect and the integrity of
the gas detection system.
The placement of the detectors should be determined in consultation with experts having specialist
knowledge of gas dispersion, with those who have knowledge of process plant system and equip-
ment involved, and with safety and engineering personnel. The location of every detector must be
recorded and available to the safety personnel. Should you require any further guidance or assis-
tance please contact DALEMANS or his local representative.
Consider the following points when positioning a gas detector:
▪
The detector should be readily accessible for maintenance and electrical safety inspection.
▪
It must be possible to fit all accessories or test equipment for maintenance and servicing.
▪
Hazard level and potential sources of gas leak must be taken into account.
▪
Consider the combination of sources of gas release with propagation effects.
▪
The detector should be protected against operational hazards of the plant.
▪
The detector should be protected against vibrations and mechanical impacts.
▪
The detector should never be positioned directly above or below a water point.
▪
For outdoor installation, a protection against rain and/or sun exposition shall be installed.
▪
The detector should not be mounted in air currents.
▪
Always observe the operational temperature range of the sensor
(refer to “
Specifications
”).
▪
To detect a gas which is lighter than air, place the detector at a high level.
▪
To detect a gas which is heavier than air, place the detector at a low level.
▪
If the gas density is close to air density, place the detector at breast height or one at high level
and another one at low level.
▪
Please note that gas density increases when temperature decreases.
The following table gives examples of detector locations depending on the gas to detect:
Gas *
Formula
Density
(air = 1)
Position
Ammonia
NH
3
0.59
High
Carbone monoxide
CO
0.97
Breast height
Oxygen
O
2
1.11
Chlorine
Cl
2
2.49
Low
Hydrogen sulphide
H
2
S
1.19
Sulphur dioxide
SO
2
2.26
* This list is not exhaustive
