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Kevin, On Sat, 2 Nov 1996, Mr. Dude wrote: > 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. I don't think the change in bag volume is going to have much of an effect on the CO2 concentration, other than as Rich points out that you are effectively venting/purging the bag. I'm sure he is right that the venting of the bag outweighs the any change in pCO2. *But*, there variable likely to have a profound effect on scrubber efficiency is: the deeper you are the more concentrated is the CO2 per liter flowing over the scrubber surface. If you are close to scrubber "capacity" at depth, as you rise the "dwell time" of the CO2 molecules is effectively increased on the scrubber bed. I would guess that this would be why the scrubber appears to work better ass you rise and also reduces your hypercapnic symptoms. Depending on the water temp at depth, if you went through a thermocline and your scrubber was not very insulated, I guess the increased temp might make a difference. But once the scrubber gets going, I doubt there are great swings in temp. So my *hypothesis* is that the reduction in hypercapnic symptoms noted on ascent when using a scrubber near the limit is due to (a) venting of CO2 form the bag (2) some contribution by gas concentration and flow over/through the scrubber. And that the shorter life of teh canister has something to do with the per minute capacity of the canister to absorb at depth, not its total theoretic absorbtion capacity. Which, by the way, is maybe why smaller cannisters won't work as well as you think they might. Hmmm. My 0.1c pH
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