In the European Union, The Rules Governing Medicinal Products in the European Union, (Vol. IV: Goodmanufacturing practice for medicinal products) includean air classification system in Annex 1 under the heading “Manufacture of Sterile Medicinal Products.” Airquality is classified alphabetically as Grade(s) A throughD, with Grade A being the cleanest. Associated witheach respective grade is the maximum allowable number of particles per cubic meter