Oil mist refers to oil droplets suspended in the air in the size range 1~10 μm.

Formation of Oil Mist

Oil mist may form when high pressure fuel oil, lubricating oil, hydraulic oil, or other oil is sprayed through a narrow crack, or when leaked oil connects with a high temperature surface, vaporizes, and comes in contact with low air temperature.

This happens while the fluids interact with the moving parts during machining.^[1]

Smaller oil droplets than oil mist are difficult to generate under normal circumstances.

Bigger oil droplets than oil mist remain in spray form; this has the advantage of a higher ignition temperature. It sinks easily, reducing fire hazard. Oil mist inside the crankcase can cause a bigger problem.

Risks

When the concentration of oil mist increases and reaches the lower explosion limit (LEL; 50 mg/ℓ, as defined by the IACS), explosion may occur when the mist contacts surfaces of over 200 °C (392 °F) or a spark.

The International Association of Classification Societies (IACS) mandates that all ships with a cylinder diameter greater than 300mm or engine power over 2,250 kW must be equipped with either bearing temperature detectors or oil mist detectors.^[2]

In regards to occupational exposures, the Occupational Safety and Health Administration and the National Institute for Occupational Safety and Health have set occupational exposure limits at 5 ppm over an eight-hour time-weighted average, with a short-term exposure limit at 10 ppm.^[3]

Related accidents

• 2010 Puebla oil pipeline explosion : The 2010 Puebla oil pipeline explosion was a large oil pipeline explosion in Mexico. In the central part of Mexico, 28 people were killed by the explosion.^[4]