The flash point of compressor lubricating oil should be:

• A. Lower than the compression temperature
• B. Higher than the compression temperature
• C. Equal to the compression temperature
• D. Not related to the compression temperature

Answer: (B)

The key idea is safety margin between the oil’s flash point and the operating temperature inside the compressor. The flash point is the temperature at which oil vapors can ignite if there’s an ignition source. In a compressor, oil is heated by compression and through heat transfer, so you want the oil to stay well below its flash point during normal operation. If the oil’s flash point were not higher than the compression temperature, vapors could flash and ignite inside the compressor, creating a fire or explosion hazard. Therefore, the correct requirement is that the oil’s flash point be higher than the compression temperature, providing a safe margin. Lower than the compression temperature would be dangerous, equal would offer no margin, and not related would ignore a critical safety concern.