Most everyday air compressors are lubricated with oil. The mechanical process of compression and thermal degradation of the lubricant can contaminate the air supply. For this reason, it is very unsafe to breathe from any air compressor not specifically designed for the purpose.
Any oil or water vapor in air supplied by an air compressor can result in pneumonia if the air is inhaled. Industrial respirators, or air fed masks, are typically protected by a series of progressively finer filters, protected by a water trap, to effectively remove contaminants.
Certain types of air compressor, such as those used in industrial respirators, are designed to provide a continuous supply of breathable air. They are, however, regulated by the Occupational Health & Safety Administration (OSHA) and the Compressed Air Association.
Air compressors designed for breathing must deliver air that has a minimum oxygen content of between 19.5 and 23.5 percent and a maximum carbon monoxide content of 16 parts per million. They must also include a temperature control and a carbon monoxide alarm.