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Date: 17 Mar 1999 14:37:14 -0500
From: Kent Lind <Kent.Lind@no*.go*>
To: cavers@cavers.com
Subject: Re: o2 for ocean deco

"Lais, Bill" wrote:
> 
> This has to be a troll, but just in case it's not:
> 
> You're probably going to be breathing the 50/50 deeper than the O2, and
> hence you'll consume more gas.  I think we learned about this concept in OW1
> if I'm not mistaken.   ;-)

> Bill

Bill, what kind of deco schedules do you run that requires more
consumption of 50/50 than O2?   Out of curiousity, I ran a sample
profile in Abyss of a square profile 20 min. dive to 200' on 19/30 with
50/50 and O2 deco gases.   Using a RMV of 0.6 cf/min Abyss
came up with deco gas usage as follows:

50/50:   22.3 cf consumed
O2:        22.8 cf consumed

On a typical deco curve, the shallow O2 stops are so much longer
than the deep 50/50 stops that you end up consuming as much or
more O2 than 50/50.  Of course, a much deeper dive profile might
produce different results.  But for ocean diving with AL40s the
above profile seems pretty realistic.

So, I think Ted's question about bottle choice is quite valid, 
especially given that it's much easier to fill 50/50 to higher
pressures and O2 is a more useful gas to have in 
reserve for surface emergencies.  I happen to use two AL 40s
for ocean deco but if I was compelled to use different
size bottles, I'd chose the larger one for my O2.  I can jam
50/50 up to 3000 psi no problem.  But I'm very hard pressed
to get more than 2000 of O2 into any bottle.

Kent Lind
Juneau, Alaska

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