Suggested Location Of Sampling Point - Bacharach HGM-SZ Installation & Operation Manual

Single Zone Gas Monitor
The SZ monitor is shipped with its leak, spill, and evacuate alarm levels set at 100, 300 and 500 ppm
respectively. Setting the monitor at these recommended alarm levels will satisfy the needs of most users.
However, the ppm levels generated by system leaks into the environment are greatly influenced by the
volume of air in the sampling area, air circulation, size of the leak, distance to the monitoring point, and a
host of other variables. In some cases the alarm set points may need to be adjusted either up or down to
achieve effective monitoring.

1.6.3. Suggested Location of Sampling Point

At the point of a gas leak, the gas is nearly pure. As gas is dispersed into the air, the gas molecules
diffuse, causing a dilution of the original concentration. The SZ monitor measures the gas concentration
at the point the sample is collected. Therefore, if the termination of the collection line is not at the exact
point of the gas leak, then the monitor will read a diluted mixture of gas and air.
It should be noted that when refrigerant and ammonia gases are cold, they are heaver than air and settle
below the leak point. When the gas warms to room temperature, it becomes lighter than air and tends to
collect above the leak point. Consequently, the sampling point should be located as close as possible to
the source of a potential leak. If this is impractical, then the alarm set points should be adjusted to
compensate for the dilution of the gas.
The SZ monitor should be mounted outside of the mechanical room or just inside a doorway to the room.
This is the "split architecture design" for safety of the operator. The monitor should be readily accessible
for easy visual monitoring and servicing. The total length of the sample line + exhaust line can be up to
500 ft (152.4 m). If the area around the monitor is not well ventilated, then an optional exhaust line and
purge line can be run to an outside location. The total length of the exhaust line + the purge line cannot
exceed 200 ft (61.0 m).
It may be necessary to perform a "smoke" test of the mechanical room to determine the best monitoring
point. The smoke test would provide the pattern of air currents present in the room.
The SZ monitor should be kept dry. When used in a wet or humid area, it is highly recommended to use
the optional water stop accessory to avoid internal damage.
Figure 1-1. Aerial View of Example Single Zone Leak Monitor Placement in a Mechanical Room
4 P/N: 3015-4256 Rev 13