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> >>>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. > Well, I think we're in agreement on that. However, I have to admit that I don't understand what the Pete is talking about. Not that I disagree - I sincerely don't understand. Pete? > 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. What it means is that the ratio of total molecules passing through channels vs. bombarding against particles should be higher at greater pressures. At a given PCO2, there will be constant number of CO2 molecules in a fixed-volume breathing loop. These molecules ought to be essentially uniformly distributed among the other gas molecules as the gas enters the canister. What I want to know is: if the total number of gas molecules is greater (i.e., the denominator is larger; FCO2 is smaller if PCO2 is constant), does this have an effect of the proportion of CO2 molecules that impact absorbent particles. Last night, my post-midnight brain said yes (due to interferrence from increased abundance of other molecules). Tonight, my post-season-premier-of-The-Simpsons brain isn't so sure. Anyone out there have a clue? > Since the total AMOUNT of CO2 in the breathing loop should not > change (FCO2) Wait, wait - the "Amount" to me means "number of molecules". This is measured as PCO2. FCO2 can change without changing the "amount" of CO2, simply by changing the number of non-CO2 molecules (i.e., the denominator) in a constant volume. In other words, the FCO2 in the loop doesn't change on ascent (unless the diver is pumping it out faster than the canister can absorb it, which would be the case if the scrubber was failing - thus leading to an ICREASE in FCO2 on ascent), but the PCO2 drops just like the partial pressure of all the other mix constituents. Well, O.K., the FCO2 could be dropping if the solenoid is firing away adding more O2, but this isn't a driect result of ascent, it's a result of the 'breather flushing the loop with O2. >, 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. I'm sure the scrubber will "eventually" pull out the CO2 - assuming your CO2 production rate drops (like if you reduce your exertion by resting, or drowning, say). A failing canister is context-senative to workload. A "failing" canister means one which does not pull out as much CO2 on a single pass as your body (via the lungs) adds on a single pass. > So it still begs the question: How come the Navy sez the scrubber does not > last as long at depth? I'm sure they have reasons - I'm hoping someone following this thread knows what those reasons are (I'm just shooting from the hip, here). > 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... I wonder who that is directed at? ;-) Rich
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