T.J.

On Wed, 26 Jun 1996 tjm@ea*.ne* wrote:

> Besides, I will have to modify mine for tech-stuff -
> computer, O.C. bailout, gas switches, etc...  Will drive the cost up
> considerably.

The issue of a computer is an interesting one. All the computers, that
this slack-jawed "prosumer" has seen, use variations of the standard
algorithms where the inspired concentration of gas is constant and the
partial pressure of the gas varies. To get the max out of your CCR, you
need a computer that takes into account the variation throughout the
dive of your FiN2 as well as depth.

Now the Pg = Fg x depth equation would indicate that all you need to do is
substitute the computer algorithm. But the laws of physics, while constant
sometimes have hidden variables in physiologic systems. What if the
absorption of nitrogen is dependent not only on the FiN2, but also on the
ratio of FiN2/FiO2? As the CCR varies the FiO2, this ratio will change.
e.g., you want to keep your pPO2 at about 1.2 At 50 fsw your
FiO2:FiN2 is 48:52, at 100 fsw the ratio is 30:70, about half. Why do I
think this might make a difference? Murphy's Law of Medicine and the fact
that the solubilities of the two gasses (O2 and N2) are not the same.
Basically I'm asking if all that matters is the pPN2 or if the relative
concentrations of other gasses, have an effect on the absorption of
nitrogen (..like the oxygen window effect).

> Let's do get a couple (of CCRs) and go diving!

Absolutely, but before I plunge to depths where time at decompression
stops is important, I would like to be sure that the assumptions I make
about nitrogen absorption when the FiN2 is constant remain true when it
varies.

I'm hoping that some of the mavens on the net can show this bu(r)bbling
diver the light.

Peter

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