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I was thinking about the potential for hypercapnia in a rebreather like the Odyssey and wondered what the endpoint inhaled CO2 will be in case of complete scrubber failure. Here is the simple analysis I came up with: Fi = inspired fraction of CO2. Fe = exhaled fraction of CO2 = 0.05 SEV. R = fracton exhausted with each breath at surface = 1/5 V = Volume of breath. P = Ambient preasure in atmospheres. At steady state the CO2 lost from venting must equal the CO2 added by metabolism. Fi*V*R/P = V*Fe/P From which we get: Fi = Fe/R = 0.05*5 = 0.25 What really concerns us is the inspired partial preasure of CO2 or PiCO2 which is PiCO2 = P*(0.25) So the end point PiCO2 can be quite large and likely fatal. However this analysis is missing something. The change in respiratory frequency when the PiCO2 rises. This would lead to Fe dropping and the end point PiCO2 dropping. Can anyone figure out how to factor in the effects of increased respiration? Does anyone have references to tests of this type of rebreather (the AGA ACSC should perform similarly )? Has anyone tried an Odyssey or BMD etc without loading the scrubber? Barrie Kovish Vancouver, Canada
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