Posted by MHK on January 04, 2001 at 15:05:14:
In Reply to: Best Mix posted by Kevin on January 04, 2001 at 12:40:46:
Kevin,
I think part of the reason that we are *vague* ( to use Seahunt's language) with respect to the proper gas issue is that we leave open the every depth equally X mix, but we do say to keep your EAD' and END's at no deeper than 100'.
By using the 100' as a target you can easily back inot a proper mix for each depth.
I would disagree with your proposal of air in the 90' - 140' range and propose a normoxic or a hyperoxic trimix at these depths. I often say that these are the subltly narcotic depth ranges where you think you're OK but you have the fuzzy head as opposed to the clear head that you'll want should there be a problem at that depth..
You want to balance your 02 and the He content to provide a margin for error with respect to the 02 content ( ie; using a P02 of 1.4 ) and adding He to allow for a clearer head. Helium is a much friendlier gas than Nitrogen and with proper stops built into your profile you'll incur little if any added decompression obligations in the 100' - 200' range. I think we would all agree that beyond 200' anything other than trimix is a receipe for disaster..
Later