Richer nitrox mixes of 40 to 80 percent O2 in small pony tanks are used for safety and decompression stops. Trimix Content: Variable mixture of Oxygen (O2), Helium (He) and Nitrogen (N2).

Divers can verify the ratio of oxygen to nitrogen in their nitrox tanks with a portable analyzer, though as you might expect, they aren’t exactly cheap. But if you’re confident in your own ...