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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 calibrated 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.
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 following
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 absolutely 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.
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