MGS-150 Manual
6309-9000 Rev4 13
consider ease of access for maintenance.
The size and nature of the site will help to decide which method is the
most appropriate to use. Locations requiring the most protection in a
machinery or plant room would be around compressors, pressurized
storage vessels, refrigerant cylinders or storage rooms or pipelines. The
most common leak sources are valves, gauges, flanges, joints (brazed or
mechanical), filling or draining connections, etc.
•When mechanical or natural ventilation is present, mount a sensor
in the airflow.
•In machinery rooms where there is no discernible or strong airflow
then options are:
Point Detection, where sensors are located as near as possible
to the most likely sources of leakage, such as the compressor,
expansion valves, mechanical joints or cable duct trenches.
Perimeter Detection, where sensors completely surround the
area or equipment.
•For heavier-than-air gases such as halocarbon and hydrocarbon
refrigerants such as R404A, propane, and butane sensors should be
located near ground level.
•For lighter-than-air gas (e.g., ammonia), the sensor needs to be
located above the equipment to be monitored on a bracket or high on
a wall within 12 in (300 mm) of(or on) the ceiling – provided there is
no possibility of a thermal layer trapped under the ceiling preventing
gas from reaching the sensor.
NOTE: At very low temperatures (e.g., refrigerated cold
store), ammonia gas becomes heavier than air.
•With similar density or miscible gases (e.g., CO or CO2), sensors
should be mounted about head high (about 5 ft [1.5 m]).
•Sensors should be positioned just far enough back from any high-
pressure parts to allow gas clouds to form and be detected.
Otherwise, a gas leak might pass by in a high-speed jet and not be
detected by the sensor.
•Make sure that pits, stairwells and trenches are monitored since they
may fill with stagnant pockets of gas.
•If a pressure relief vent (PRV) pipe is fitted to the system, it may be a
requirement to mount a sensor to monitor this vent pipe. It could be
positioned about 6 feet (2 m) above the PRV to allow gas clouds to
form.