The international standard ISO 8573-1 (2010), “Compressed air — Contaminants and purity classes,” provides a classification system for the main contaminants in compressed air systems. The standard specifies a number of purity classes for compressed air with respect to particulates, water and oil, independent of the location in the compressed air system at which the air is measured. In addition, it identifies gaseous and microbiological contaminants in a system.