. Our computers can be set to 21% Oxygen and the regs, BCs and guages are only 1 year old and can be used with EAN.
BEM, why would you set your computer to 21% oxygen?
The concern with NITROX is tank and valve cleanliness. This is related to the practice of partial pressure filling where the tank is prefilled with a certain pressure, usually around 400 psi, of pure O2 and then topped off with compressed air. Most new tanks and valves are usually clean enough from the factory to tolerate O2. However, there is a great deal of conservatism and black magic surrounding this subject. It involves special O ring materials and routine cleaning with special chemicals or detergents, and unique NITROX certification and stick on labels.
Filling a NITROX clean tank with a standard compressor of modern design will not have any appreciable effect on tank cleanliness. However, after many such fills it is theoretically possible to deposit enough hydrocarbon film in the valve or tank to cause a mini O2 combustion resulting in some fumes inside the tank. Actually finding a case where this has happened is difficult. When actual problems have been documented they almost always involve a tank valve or regulator which has been heavily lubed with silicone grease. That stuff, in visible quantities, is combustible in high pressure O2.
There are alternate methods of filling called membrane separation, decanting and mixing, and/or continuous blending which do not inject pure O2 into the tank, and cleanliness is less of a concern to the industry. Still, individual shops may impose their own rules or requirements. They own the equipment and the gas and they do the filling.
One note about aluminum. Aluminum, although a metal, is combustible. The source of combustion can be small metal chips, oil or grit inside the tank. Also, older tanks are sometimes subject to stress cracking. For these reasons, it is a good idea to keep NITROX tanks made from this metal as clean as possible of oils and grit. Not to scare anyone unnecessarily as this is more of a curiosity at recommended O2 fill rates and pressures. However, hot filling an aluminum tank with pure O2 to 3000 psi would raise such concerns to a serious level. Therefore, cleanliness is doubly important in such cases.
