GD1 Page 63 of 76 850-816926-EN R06
10.3. Positioning considerations
Open path detectors are more susceptible to external interference compared to point
detectors. To avoid performance reduction and downtime, the following should be taken
into consideration when choosing mounting location.
The detector should be attached to a mechanically rigid structure to help keep the unit in
alignment due to influences such as:
• Thermal movement due to the effects of the sun and temperature changes
• The effects of strong wind, vibration from equipment such as pumps, turbines and
cranes, high-pressure flushing of the detector etc.
• Other mechanical effects, particularly in high-traffic areas.
The measuring path should be horizontal to minimize environmental effects such as rain
and snow. Other factors to be taken into account could be temporary scaffolding, large
vehicles etc.
10.3.1. General positioning considerations regarding a gas cloud
The concentration of a gas cloud rapidly reduces as the distance from the leak source
increases. The detector should therefore be placed as close as possible to potential leakage
sources. Normally prevailing wind directions must be taken into account when positioning
the detector.
Positioning height of the detector should also be taken into consideration. H
2
S is heavier
than air and has a tendency to accumulate in low areas. Due to the H
2
S being heavier than
air the detector should normally be positioned at low heights.
In places where there can be thick fog or heavy snowdrifts it is recommended to keep the
measuring path as short as possible.
Even if GD1 is practically solar blind, positioning the measuring path in a North – South
direction is preferable to avoid direct sunlight.
The performance of an Open Path gas detector is influenced by:
• Distance from leak source
• Weather and environmental conditions
• Temporary or permanent path obstruction
• Leakage characteristic (pressure, size, fluid, temperature)
• Gas density (heavier or lighter than air)
• Vibration and stability of mounting structure
• Exhaust or steam discharges hitting the optics.
The detector should be placed according to a gas dispersion analysis taking into account all
the factors above.
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