Lubricating oil flammability

Lubricating oils used in refrigeration and air conditioning systems can burn, so care must be taken by service technicians to prevent them from catching fire.

Prior to the phase-out of CFC refrigerants, mineral oils were the primary oils used in refrigeration and air conditioning systems. However, mineral oils are not suitable for use with new HFC and HFO refrigerants. As a result, synthetic oils such as alkyl benzene, polyol ester, polyalphaolefins and polyalkaline glycols were developed to meet the requirements.

You should use only the lubricant recommended by the compressor manufacturer. Oil producers and compressor manufacturers go to great lengths and expense to develop and test new lubricants. There are tests for viscosity, floc point, pour point, flash point, etc.

Two of the important properties of refrigerant oils are:

FLASH POINT: The flash point is the lowest temperature to which a lubricant must be heated before its vapour will ignite when mixed with air and in contact with a naked flame, but it will not continue to burn when the flame is removed. The flash point varies from 90 to 2500C.

FIRE POINT: The fire point is the temperature at which lubricant combustion will be sustained. The fire point for a lubricant is usually 8 to 10 percent above the flash point.

This means that if synthetic oils are exposed to any naked flames, while silver brazing for example, they will catch fire, burn and produce toxic and irritating fumes, CO and CO2.

For people with a stationary refrigerant handling licence this would have been covered in the relevant qualification’s unit of competency on recovering, pressure testing, evacuating, charging and leak testing of refrigerants.

Service technicians are therefore reminded of this fire hazard and the procedures to:

  • Prevent synthetic oil from catching fire, which is to ensure it is not exposed to naked flames while servicing the refrigeration/air conditioning equipment.
  • Extinguish the oil fire in the recommended manner. Generally, this means removing the naked flame and using dry chemical, foam or carbon dioxide fire extinguishers, not water.

Remember to always refer to the oil manufacturer’s Material Safety Data Sheet (MSDS) for its specific flammability, extinguishing media and hazardous combustion product details.

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