O2 cleaned and O2 service rated cylinders maintain their rating if filled with:

Oxygen-compatible gas maintains the rating of O2 cleaned and O2 service rated cylinders because these gases are specifically formulated to be compatible with the cleaning processes that ensure the removal of any contaminants that could ignite in the presence of oxygen. When cylinders are rated for O2 service, they are cleaned to a certain standard that makes them safe for use with high concentrations of oxygen.

Using an oxygen-compatible gas ensures that there are no residues or materials that could react negatively in a high-oxygen environment, thereby preserving the integrity and safety of the cylinder. This is important for preventing potential hazards such as combustion or explosion, which can occur if the cylinder contents are not appropriate for high oxygen environments.

Other gases, such as regular air or any gas that isn’t certified as oxygen-compatible, could contain impurities or substances that might ignite in the presence of elevated oxygen levels, thereby compromising the cylinder's rating and introducing safety risks. Therefore, only filling the cylinder with approved oxygen-compatible gas ensures that the integrity of its O2 service rating is maintained.