It requires a tight fitting respirator and is supplied by an on-line compressor or compressed air cylinder. It enters the breathing air system through the air intake, or is produced by overheating of piston type compressors. The air intake must be placed away from engine exhaust or other sources of carbon monoxide. As compressed air flows through the system, it cools, causing the vapor to condense in the facepiece or helmet. Moisture combines with oil and solid contaminants to form sludge, which can clog or damage system components.
Water also causes rust in pipelines, and can freeze in cold weather to block air flow.
In reciprocating compressors, lubricating oil applied to cylinders causes small droplets by the shearing action of the piston to enter the air system as a mist. Oil mist can cause breathing discomfort, nausea and pneumonia, and create unpleasant taste and odors. Centrifugal compressors are oiless. Solids Solids generally enter the system through the air intake. However, some materials may be introduced by the compressor itself.