When does my cylinder or valve need to be Nitrox Ready?
The recreational diving industry has widely followed what is often referred to as the “40% Rule” which states the cylinder and valve must be Nitrox Ready only when they will be exposed to a gas mixture containing more than 40% oxygen. While sport diving Nitrox and technical diving Trimix don’t absolutely require that the cylinder and valve be Nitrox Ready, many fill stations blend directly in the tank by first adding 100% oxygen and then topping off with oxygen compatible air. This process, known as partial-pressure blending, requires that the cylinder and valve be Nitrox Ready. In practice, almost all Nitrox and Trimix cylinders are Nitrox Ready because partial-pressure filling is so common. You should keep in mind that not everyone agrees with the 40% rule. Luxfer has an extremely detailed statement of their position on aluminum cylinders and oxygen which argues any cylinder that contacts more than 23.5% should be oxygen clean.
