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David, I can't keep up with all of this. To me it is obvious, but to
communicate it correctly another story. I give up trying.
inal Message-----
From: David Chamberlin <dwc@na*.co*>
To: Trey <trey@ne*.co*>
Cc: Tech Diver <techdiver@aquanaut.com>
Date: Friday, June 16, 2000 11:40 AM
Subject: Re: Deco gas selection


>Trey wrote:
>>
>> What the fuck are you talking about? I never use trimix above 21% Oxygen
>> below 120 feet. It is stupid.
>
>That's what I would've thought, and that's why I asked the question.
>The person who responded in private e-mail was someone I thought was
>very knowledgeable about DIR SOP, so I wanted to go straight to the DIR
>source and find out 1) if that was in fact the recommended gas and 2)
>Why that would be selected.
>
>> The use of ONE gas for deco imples 50% - we
>> have been over this,
>
>Sorry.  I tried doing a search for this topic and the only responses I
>came up with were the ones I posted earlier which didn't really cover
>the "why's" of the choice of 50/50.  So I was attempting to get more
>information and clarification.  As I said in my earlier post, I'm not
>doubting what you are saying is correct - I just want to understand it
>better.
>
>> Everyone else has been over
>> this. Wake up.
>
>I'm sorry.  As I said before, I tried to find earlier posts on this and
>I only got some scattershot and very brief messages, which is why I
>posted the question.  So let me try an abbreviated form of my question.
>I'm going to state what I think the rationale is for using 50/50 for a
>one gas dive to depths <=50m with times <=30 min, in spite of what seems
>to be contradictory information from the Baker's Dozen.
>
>1) The 50/50 let's you open your oxygen window earlier and thus you
>clear out most of your deco earlier, so you don't have to do so much
>"damage repair" at the shallower stops.
>
>2) The benefit of clearing out your deco earlier outweighs the fact that
>deco on 50/50 will not be as beneficial at the shallower stops.  And
>since you cleared out most of your deco early, you don't need to be as
>efficient at the shallower stops.
>
>3) The Baker's Dozen is comparing 80/20 at a depth of 30FSW, to 100% at
>a depth of 20FSW. The difference in depth between these two is not
>significant enough to apply the reasoning of 1) and 2) to 80/20, and
>thus 80/20 pretty much has all the downsides and none of the upsides.
>
>And finally, I'd like to reiterate one of my questions in my previous
>post.  You had said, "Most of my ocean dives are one gas dives - I do
>not generally see the need for the oxygen at all on a short hop first
>dive, and prefer not to take the
>beating of using it for not reason."  What is the beating you are
>referring to?  Have you found that these types of short exposures to
>high (1.6) PO2s actually have longer-term effects?
>
>Thanks,
>Dave
>--
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