As I study to get ready for the CCR class, I discovered something that may be obvious to many but was definitely not to me. “Surface intervals are not always the most efficient way to off-gas nitrogen after a dive”. Depending on the blend, there is an optimal depth at which the off-gassing is fastest and a range of depths at which it is faster than air on surface.
- As long as you have a blend with more than 21% O2, there is always a depth that gives you ppN2 lower than .79 bar and hence is more efficient that being at the surface breathing air. Some examples are 6m for EAN50, 14m for EAN67 (the most efficient nitrox mix for off gassing), 6m for O2.
- Adding He increases the optimal depth for off gassing. E.g., 8m for 21/35, 11m for 18/45, 30m for 10/70
- When not using He, the optimal depth is 11m
- When using He, the more He the deeper is the optimal depth. E.g., 17m for 21/35, 21m for 18/45, 39m for 10/70