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11.Leak detection methods
The following leak detection methods are deemed acceptable for systems
containing flammable refrigerants. Electronic leak detectors shall be used
to detect flammable refrigerants, but the sensitivity may not be adequate,
or may need re-calibration. (Detection equipment shall be calibrated in a
refrigerant-free area.) Ensure that the detector is not a potential source of
ignition and is suitable for the refrigerant used. Leak detection equipment
shall be set at a percentage of the LFL of the refrigerant and shall be ca-
librated to the refrigerant employed and the appropriate percentage of gas
(25 % maximum) is confirmed. Leak detection fluids are suitable for use
with most refrigerants but the use of detergents containing chlorine shall
be avoided as the chlorine may react with the refrigerant and corrode the
copper pipe-work. If a leak is suspected, all naked flames shall be removed/
extinguished. If a leakage of refrigerant is found which requires brazing, all
of the refrigerant shall be recovered from the system, or isolated (by means
of shut off valves) in a part of the system remote from the leak. Oxygen free
nitrogen (OFN) shall then be purged through the system both before and
during the brazing process.
12.Removal and evacuation
When breaking into the refrigerant circuit to make repairs or for any other
purpose conventional procedures shall be used. However, it is important
that best practice is followed since flammability is a consideration. The fol-
lowing procedure shall be adhered to:
Remove refrigerant; Purge the circuit with inert gas; Evacuate; Purge again
with inert gas; Open the circuit by cutting or brazing.
The refrigerant charge shall be recovered into the correct recovery cylinders.
The system shall be flushed with OFN to render the unit safe. This process
may need to be repeated several times. Compressed air or oxygen shall not
be used for this task. Flushing shall be achieved by breaking the vacuum
in the system with OFN and continuing to fill until the working pressure is
achieved, then venting to atmosphere, and finally pulling down to a vacuum.
This process shall be repeated until no refrigerant is within the system.
When the final OFN charge is used, the system shall be vented down to
atmospheric pressure to enable work to take place. This operation is abso-
lutely vital if brazing operations on the pipe-work are to take place. Ensure
that the outlet for the vacuum pump is not close to any ignition sources and
there is ventilation available.
13.Charging procedures
In addition to conventional charging procedures, the following requirements
shall be followed. Ensure that contamination of different refrigerants does
not occur when using charging equipment. Hoses or lines shall be as short
as possible to minimise the amount of refrigerant contained in them.
Cylinders shall be kept upright.
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