This standard applies to proportioning units intended to produce synthetic medical air and air for driving surgical tools by mixing in defined proportions oxygen and nitrogen. This standard applies to proportioning units intended to be components of a medical gas supply system for medical air which supplies a medical gas pipeline distribution system complying with ISO 7396-1. The number of proportioning units within the medical air supply system and their combination with other sources of supply (e.g. cylinder manifolds) to ensure that the supply system consists of at least three sources of supply is outside the scope of this standard. Requirements for the supply systems for medical air are given in ISO 7396-1.