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> Since we are concerned about exposures to elevated PO2's,
> it seems to me that we should be considering the use of "airbreaks"
> during the deep decom stops (ie, take an "air break" prior to starting
> onto nitrox during decompression).  

John,

I'm not sure what to suggest for your question, but it prompted me to post
another related question/problem.

For those of you who plan to eventually use fully-closed rebreathers, and
who intend to use high PO2 setpoints (and I consider 1.4 the highest
setpoint a reasonable person would ever want to use), you're exposed to
the setpoint PO2 for essentially the entire dive (as opposed to
open-circuit, where you experience your max PO2 only at your max depth).
With a setpoint of 1.2-1.4, you're likely to be making dives where you're
limited by your "CNS O2 clock" and OTUs.

My question is; what's the best way to optimize/maximize bottom times?  Is
it more effective to use a lower setpoint (=more decompression time) for
the entire dive, or is it better to keep a higher setpoint (1.2-1.4) and
periodically take the equivalent of "air breaks" by dropping the loop PO2
for a few minutes? It's not as simple as just working out the math, when
you take into account things like probability of O2-induced convulsion,
etc. (I don't think the math for various "oxygen clocks" has much basis in
physiological reality anyway...)

I suspect that the latter alternative would be the better approach, but
how low should the PO2 be on the "low-PO2 breaks"? O.5, as John suggests? 
How long? 5 minutes? With what frequency? 20 minutes? Should they be done
throughout the course of the dive, or only during decompression? Only
after the accumulation of XXX OTUs or whatever O2 clock you go by?

Anybody with a lot of knowledge/experience with O2 exposures have any
suggestions?

Aloha,
Rich

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