Oil/water separators using a settling tank and a weir device are commonly used by manufacturing industries to remove oil from condensate extracted from compressed air systems, so that the bulk of the condensate can be safely put into a 'foul' drain system. Consider, however, that the settling tank contains many litres of condensate contaminated with oil and allowed to stew in a nice warm compressor house. It should not surprise anyone that after a few weeks, the settling tank is a bacteria-laden broth awaiting unsuspecting and unprotected victims.

It is very likely that both airborne and waterborne pathogenic bacteria such as Pseudomonas and Legionalla will be present in large quantities and will cause problems to even healthy people if inhaled or if brought into contact with mucous membranes or open wounds.

The necessity for the liquid to remain undisturbed in this type of machine to allow oil to settle out precludes the use of treatment such as chlorine to kill the bacteria; in practice, no one is in danger because the broth is contained in a tank and is unlikely to cause any problems while in an undisturbed state.

This type of machine, however, needs to be regularly maintained and will almost certainly need to be emptied and cleaned out at least annually and a pressure washer is usually used for this.

This maintenance and cleaning not only brings people into contact with the fluid, but can also create dangerous aerosols.