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This is what Pete Heseltine had to say about CO2.  Kinda interesting:

>>>Re the CO2 thing. CO2 goes in and out of solution very easily. So the
atmospheric pressure is less important than the concentration to which you
are exposed, i.e., the total molecules, regardless of the volume they
occupy. The range of tolerance is so small, you are really huffing at a
pCO2 of 0.06 ATA, that for practical purposes you have no margin, like you
do with O2 toxicity (say 0.12 ATA to 1.6 ATA). So as you rise the issue is
whether the nitrogen (approx 60% of the bag's volume) expands and
"prevents" and inflow of O2, in a volume dependent system. The CO2
expansion is not likely to "displace" the other gasses, because it will
kill you long before it will displace enough O2 to make you hypoxic.<<<

So that would seem to indicate that I was somewhat right about pCO2 having
an effect on a diver at depth, since the pCO2 would drop upon ascent, the
symptoms of hypercapnia should reduce.

Rich, part of me sees the logic in your "higher pressures means the CO2 can
pass through the channels easier" but I don't know if that is exactly the
case.  Since the total AMOUNT of CO2 in the breathing loop should not
change (FCO2), the ability of the scrubber to EVENTUALLY remove all those
molecules shouldn't either.  Notice the "eventually" since I'll grant that
maybe higher pressures allow some CO2 molecules to pass the scrubber at
least once without banging into a sofnolime pellet.

So it still begs the question:  How come the Navy sez the scrubber does not
last as long at depth?

I know all this is a bit academic, but its nice to explore the physics and
physiology of these systems, rather than rag on who has the best
rebreather, or who pumps iron at 5:30 in the morning when he's supposed to
be reviewing Outlines that I stayed up 'till 1 AM writing...

Later,

Kevin.
HeyyDude

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