oxygen ccr for deco

[jasondrake]

Thinking about decompressing on an CC oxygen rebreather. Does anyone know how much inert gas is washed out of you into the loop after a given exposure? How much N2 does the body contain (in volume corrected for 1ATM) when saturated at say 40 metres. If you catch my drift. Or how much N2 is dissolved in the body at the surface, ie 1atm? Are we talking litres, hundreds of litres? Are there tables for loop flushing? (I'm sure it could be worked out with a periodic table and a calculator but I'm bone idle.)

[peter k]

At the surface you've got about 1ltr dissolved and if my calcs are right at 40mtrs you have about 2 1/4 ltrs if your saturated. Sorry I can't answer your other questions.

Peter

[peter k]

In fact, I think I made that harder for myself there. It might just be a straight 5bar/5ltrsN2 at 40.

Peter

[jasondrake]

Seems to make sense, a linear relationship between volume absorbed and pressure. So in practical terms occasional flushing of a, say, 5 litre loop will do the job. Could calculate deco. for a 90% nitrox mix to be safe. Thanks for reply

[Mark Scott-Simons]

Its called Henry's Law and if you are diving a CCR and using a Buehlmann model then its only the ppO2 that matters not the FO2. So as long as the ppO2 is correct for the plan, then your off gassing will be as the deco tables predict.

If you can find a copy Oxygen and the Diver by Kenneth Donald it has the answer to your question. In brief one set of experiments when using O2 RB the FO2 varied from 92-97% and that was with lots of initial loop flushes.

Scotty