Posted by MHK on March 21, 2001 at 15:37:14:
In Reply to: Re: tri mix cert. posted by AADIVER on March 21, 2001 at 14:24:52:
Frank,
I disagree that after a fill you'll be back to 79% N2..
When you and I were on the boat we discussed this issue but just so I can elaborate for the benefit of the other's.
I often use double AL 80's for any dive under 200' and will generally bring these filled with a 32% or 36%, or perhaps a mix with some He in it to start my day. And I'll note the theory behind the logic is the same irrespective if I'm diving single or double tanks. I have just simply settled in on using AL 80's for the recreational stuff to take advantage of the increased levels of F02.
My RMV is .5 and a set of double AL 80's will generall last me 2 or 3 dives of average depth 100' and average time 30 minutes and as such, to the extent that I do need to *top off* I'm starting with increased levels of F02 and unless my tank is completely empty no matter what happens I'll have added F02's and/or He..
I have always suggested Nitrox from 0' - 100' in my primary gas supply but I have never shyed away from He at those depths. My deco gas usually includes 25% He @ 70', but may be beyond the scope of this discussion.
The benefit of He in the mix and the inclusion of deep stops is that you can DRAMATICALLY increase your recreational NDL limits. If you get into tech diving it's a foregone conclusion, but I'm trying to address the average every day diver..
If you provide your avergae profile, your average fill along with your RMV I'll give you specifics of how by putting He in your tank to start will not result in your tank being at 79% after the 1st dive...
Later