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• If the concentration is above the upper flammability level ( UFL ) of approximately 8.9 % there is insufficient oxygen for combustion .
• The LFL is approximately equal to 35 g / m3 of HC refrigerant in air . For safety reasons a practical limit of 8 g / m3 of HC in air should not be exceeded in a closed space .
Consider the fire triangle – oxygen , fuel and an ignition source – all three have to be present for fire to be maintained . Remove any one of the three and combustion is not possible . For combustion there must be an ignition source . The ignition source must be hotter than 460 ° C to ignite the R600a refrigerant .
The following represent potential ignition sources :
• Static electricity
• A flame , such as from a brazing torch , halide torch , match or cigarette lighter
• A spark from an electrical component such as a switch , thermostat , starting relay , overload protector or loose wiring connection show the type of refrigerant and that it is flammable . This label should not be removed .
The guidelines below are similar to the guidelines for any refrigerant cylinder :
• Do not store HCs indoors
• The valve cap should be fitted when the cylinder is not being used
• If a cylinder needs to be heated it should be placed in a container of water no hotter than 45 to 50 ° C
• The cylinder and its valve should not be modified
• The cylinder should not be re-filled unless it is designed for recovered refrigerant
DESIGN OF HC APPLIANCES HC appliances usually have electrical components that are either :
• Sealed
• Solid state
• Enclosed in a sealed box
• Located remotely from the refrigeration circuit
We need to realise that combustion will not occur inside the system as there will not be enough oxygen present . Even if a system is not evacuated before charging , there will not be enough oxygen for combustion . Combustion can occur if a leak of HC results in a flammable mixture and there is an ignition source .
Refrigerant R600a leakage can be dangerous if :
• Refrigerant leaks into a closed cabinet ( or other sealed space ) and there are electrical components inside the cabinet . Consider those custom kitchens with the fridges built in
• Refrigerant leaks into the air around the system and there are sparking electrical components on the system
• Refrigerant is lost during servicing ( for example , when venting , flushing or charging a system ), and there are sparking electrical switches and / or flames
Margaret , the flammability aspect requires some simple workplace precautions :
• Work in a well-ventilated area , or outside
• No smoking
• Demarcate the area using applicable signs
• No flames within 2m of the charging / venting area
• Do not use switches or any ignition source within 2m of the charging / venting area
• Use tools and equipment designed for use with HCs
• Have a fire extinguisher ( dry powder type ) on hand
• Use your personal protection equipment ( PPE )
• Remember that HCs can accumulate in chest cabinets and basements
HANDLING R600A CYLINDERS Cylinders containing HC refrigerants should be clearly labelled to
This avoids the risk of combustion if HC refrigerant leaks from the circuit . When replacing these components you must use the same type and fit them in the same position . If you need to open a sealed enclosure , make sure you re-seal it correctly .
SERVICING PROCEDURES WITH HC REFRIGERANTS Servicing procedures for HC refrigerants are similar to those for R134a , except for the additional precautions needed for working with flammable refrigerants .
We will look at :
• Safe venting of HC refrigerants from systems
• Removal of remaining HC refrigerant
• Replacing system components
• Pressure testing
• Leak testing
• Evacuation
• Charging
• Sealing the process tube
• Leak testing of process tube
SERVICE PRACTICE
• Remember that an HC and air are flammable and can be ignited by any ignition source .
• The HC refrigerant should be vented to an area away from ignition sources such as flames and sparks , preferably outside .
• The best tools to open the system are piercing pliers or a piercing valve , with a long hose connected and vented outside .
• Run the compressor , piercing pliers or a valve are not necessary if the process tube already has a connection on it .
www . refrigerationandaircon . co . za RACA Journal I May 2023 43