Posted by MHK on March 21, 2001 at 15:47:04:
In Reply to: Rec tri mix cert. posted by Divenerd on March 21, 2001 at 12:55:25:
It all depends... More often than not the answer is no. In GENERAL ( meaning that there are exceptions to this rule) if you do a dive on air -v- a dive with a touch of He in the mix along with deep stops the NDL limits are virtually the same...
The thing to remember and I'll continue to emphasis as we keep going, is that He uptakes at 2.65 time the rate of N2 and by the same token *off-gases* 2.65% fatser. At the deeper depths ( ie; 60' - 130') you're dealing with the *fast* tissue compartments, so staying a minute or so at 45' or 30' does a few things:
1) It helps control the ascent;
2) It allows for the fast tissue compartments to clean up before you get to 15';
3) It provides long term cell rigidity benefits;
4) It's an easy breathing gas, and as such you don't need to work that hard;
5) It's more difficult to get a C02 buildup;
6) It provides for a clearer head..
The benefits of He are virtually undisputed, but basically the only drawback is the cost.
Jim Hoffman can speak better to the cost issue than I can so I'll defer to him in that regard...
Later