The 2004 US FDA “Guidance for Industry Sterile Drug Products Produced by Aseptic Processing – Current Good Manufacturing Practice” 2004 [30] provides the following nonbinding recommendation regarding the filtration of compressed air and other process gases:“A compressed gas should be of appropriate purity (e.g., free from oil) and it’s microbiological and particle quality after filtration should be equal to or better than that of the air in the environment into which the gas is introduced. Compressed gases such as air, nitrogen, and carbon dioxide are often used in cleanrooms and are frequently employed in purging or overlaying.”ISO 8573 [31] is a universal standard that applies to all industrial uses and provides some information that is applicable to the pharmaceutical industry.