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Dave,

> I have two questions:
>
> 1) in regard to the 80/20 I have been using:  I was taught that this was
the
> safer gas in our diving environment because of a fear of O2 toxicity.  My
> plan wasn't to breath it @ 30fsw; I was making my switch at 25fsw, after
> clearing my 30 ft. stop.  Rather, the idea was to avoid pure O2.  I
addition,
> the surface conditions can change rapidly in the north Pacific of Carmel,
CA,
> and a 10-15fsw deco can be difficult.  I do run all my profiles through
> calculations to watch for my CNS clock, which usually is between 23-37%.
My
> hangs above 30fsw are usually 15-25mins.
>
> Is this really an issue?  If it is an issue, at what point do I need to
> schedule a break from breathing O2?  Should I breath my 50/50 during the
O2
> break and for how long?

Do not use EAN80 for deco, read the "bakers dozen" mail from George Irvine
why. Pure O2 for your last stop at 20ft is what you want to dive. You do
breaks to your back gas (trimix) after every 20min on O2 for 5 min. Keep the
deco clock running while you are on your back gas, do not stop and resume
counting your stop time when you are back on O2. That is not neccessary.

> 2) Concerning an ascent from 200fsw after a 20 min. bottom time on 18/40
> Trimix.  Would an appropriate plan be to do short deep stops starting at
150
> fsw, up to 60fsw where the switch to 50/50 is made, until 20fsw, where O2
is
> started?  How is the ascent made from the first deep stop to the switch to
> 50/50?

If you take O2 into account for your END, you should get some more helium in
the mix. Something like 18/55 would be a real 100ft air equivalent.
FO2+FN2/.79(D+33)-33 is the formula.
I would start my deep stops even around 160ft and use EAN50 from 70ft up.
Every 10ft stops of 20-35 seconds up to your first stop works fine for me,
don't know what all others on the list are actually doing.

Regards,

THOMAS

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