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Rich Pyle wrote
  If you 
>suggest that a canister will give you more hours in shallow water than in 
>deep water, I would be skeptical.  I have no doubt that absorbent 
>efficiency is affected by pressure, but I do doubt that the difference in 
>efficiency at depth vs. shallow is enough to significantly affect the 
>operational time of the rebreather, if you're only considering the short 
>period of time you're on OC

Hi 

Well from what I have read you are right and wrong.  

The USN recommendation for the MK16 cannister duration during cold water
dives do show a dramatic reduction in time for deep dives.  At 30 to 40
degrees using nitrogen oxygen mixes the rated life falls from 300 minutes to
only 100 minutes when you dive deeper than 50', however when the water is
warmer than 70 degrees there was not reduction in rated scubber duration
with depth.

I will look around to see if I can find the original NEDU work this
recommendation is drawn from and post it .

My own experience in cold Canadian conditions support those recommendations.
I exhausted the cannister on one of Barrie and my homebuilt units at 145' (
I had been doing a bunch or short field tests and had been sloppy with
recording how long I had spent on the cannister ( don't bother to call me a
dumb shit I already know!))  Using a combination of dumping the last third
of each exhalation and slowing my breathing rate to increase scrubber
residence time I was able get the co2 levels down to a tolerable level.
When I returned to the shallows the scrubber seemed to work much better.
Like Mike the sorb was totally violet  but unlike Mike my exertion levels on
the bottom were quite low.

I have also run the cannister to near exhaustion on purpose in the shallows
and noticed  the co2 absorbtion seemed to slowly be reduced whereas the
scrubber seemed to run out much more abruptly at depth.

Rich when you say that the indicator is unreliable what do you mean and how
did you arrive at this conclusion?  BTW the manufacturers say the same thing
but I am interested how you determined this.

Bill

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