Posted by MHK on November 17, 2000 at 11:14:49:
In Reply to: Re: P.S. posted by AADIVER on November 17, 2000 at 10:24:20:
Frank,
Most of the guys that I know using Heliox above 100' are using it as a decompression gas, as opposed to a primary bottom mix.
I just ran some numbers in terms of substituting a EANx 40% at 90' for a straight Heliox consisting of 40% 02 and 60% He and the results are unecessarily conservative:
90' at EANx 40% = MOD at 1.4, 83' at 1.5 91' and at 1.6 99' with an EAD of 60'.. While the MOD's are a little rich for my taste we can address that later..
90' at Heliox 40% 02 and 60% He = same MOD's as above but with a END of the surface. While this is brilliant it is also unnecessary..
A more prudent mix to the extent that you desire 90' using a 40% 02 content would be something along the line of a hyeroxic trimix of 40/30.. This provides for an END of 13' a P02 of 1.49 ( which I'll talk about later )...
I like to keep my P02's at 1.4 for the working portion of my dive so I'd go with a 38% 02, but for purposes of this analysis I kept it at 40% per your request..
Furthermore, I didn't see John's post that you were referring to but I've dove with John a lot and I know he favors a trimix something of the fashion that I just recomended so we should clarify the fact pattern..
I have been strongly advocating using a Nitrox mix for the Yukon, but I'm equally as excited about the notion of a hyperoxic trimix.. In fact the last couple of dives on the Yukon Walker, Terry and myself have used trimix and have enjoyed 60 minute BT's and have really had the opportuinty to explore the wreck and have done so with a very clear head and minimal decompression obligations such that we didn't even take deco gas and deco'd out on back gas...
Hope that clears it up a little..
Later