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Mike, Interesting you would choose to go to Open Circuit to relieve your symptoms. My suggestion would be to do what Leon trained me (us?) to do in that situation, which is to go semi-closed on the rig itself. You get the benefit of the higher ppO2 in the loop, maintained by the unit, and are able to flush the system of CO2 as you go along. I still practice purging my loop, every now and again. Leon suggested a full purge every 3 minutes if you feel the symptoms of hypercapnia. You also avoid having to remove the CCR mouthpiece underwater (unless you're on the AGA with the DSV able to switch between OC and CC). Opening and closing of the valve on the mouthpiece keeps water from flooding the loop, but some water is introduced when going back and forth. The absorbent pad should take care of most of it, but I'm in the "I-don't-want-any-extra-water-in-my-loop" mode anyway, so would elect to go semi-closed before bailing on the mouthpiece and going to OC. When I had my little "experience" - I went to semi-closed AND open circuit intermittently to continue through deco, but I had the AGA with the DSV, so it was merely a flip of the switch to go between CC and OC. An interesting question that I'd like Rich and Rod to answer is this: If you have elevated CO2 at 140, like you reported, and you ascend, does the concentration dose of the CO2 lower as well, or is it independent of depth? If it is the former, rather than the latter, would this explain the lessening of perceived hypercapnia symptoms? I think I know the answer already - that is that the CO2 concentration would be lowered as you ascend and the gas expands, but am not completely sure. One thing that the Rod-man suggested to me, which I have practiced a lot in my last few dives, was to use the hydrostatic pressure differential found in our units to your advantage in situations where you feel that you can't catch your breath, or are getting a headache: (Rich can ignore this, since the Cis Lunar explodes when CO2 levels raise above spec). He told me that I should lean backwards, with the cannister lower than my head, and take full breaths with the unit positively pressuring my lungs. I tell you, it works fantastic. On my last dive, I swam like a dog against the current, just to get myself huffing and puffing like hell - I then stopped (I was in 50 fsw) leaned back and took some deep breaths. Damn. Felt goooood. I thanked ol' Rod there and then for that tip. Got my breathing rate down within seconds. Now, as for what I would do, iffin' I were you... I'd just change scrubber more often. The stuff is cheap when compared to the other things we have to buy for these rigs, so maybe a Hoover like you should change it more often, or reduce your intake of Pop Tarts, which is known to increase vascular CO2 levels when fed in mass doses to laboratory rats... Also, storing your sofnolime in an open bucket next to Kimo's '56 Chevy exhaust in the garage isn't a good idea. Just my thoughts. Kevin HeyyDude
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