Editing Nitrox (section)

===United States===
[[File:Cylinder mod.jpg|thumb|right|Cylinder showing Nitrox band and sticker marked with maximum operating depth (MOD) and oxygen fraction (%O<sub>2</sub>)]]
Every nitrox cylinder should also have a sticker stating whether or not the cylinder is ''oxygen clean'' and suitable for partial pressure blending. Any oxygen-clean cylinder may have any mix up to 100% oxygen inside. If by some accident an oxygen-clean cylinder is filled at a station that does not supply gas to oxygen-clean standards it is then considered contaminated and must be re-cleaned before a gas containing more than 40% oxygen may again be added.<ref name="Butler 1992" /> Cylinders marked as 'not oxygen clean' may only be filled with oxygen-enriched air mixtures from membrane or stick blending systems where the gas is mixed before being added to the cylinder, and to an oxygen fraction not exceeding 40% by volume.