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Rich responded to my note on O2 tox.  I in turn agree with what he pointed
out, but would like to add some info.

Rich mentioned that the guy who died recently on the Doria, presumably from O2
tox, was in the middle of his dive.  Here's what I have heard about this dive.
This is admittedly second hand, but I heard it from three separate guys who were
all on the boat, so I hope there is some grain of truth in it.  Apparently, the
two divers involved were after 2nd class china, and were working on air at
around 220-230 fsw (1.67 ATAs PO2, so already into exceptional O2 exposure).  
They got lost and silted out, blew their planned bottom time of 15 minutes,
and exited the wreck at 30 min. with empty tanks. Unless they were superhuman
divers, I bet they were breathing like jet engines at this point and probably
had really healthy PCO2s in their blood (predisposes to O2 tox, as Rich noted).

They blasted up the line to surface-fed O2 at 20 fsw (1.6 ATA PO2), and breathed
that for 45 min,  emerging from the water without symptoms.  Their CNS O2
clocks, by the way,  should have been well beyond NOAA limits by this point. 
They then waited 4 hours on the surface, and did essentially the same thing
(went to 230, got lost, blew their bottom time).  Only this time, one of the
divers siezed and didn't make it out. 

Now as I recall, your CNS clock is assumed to back off by 50% for every 4 hours
of normoxic exposure (I'd have to check this to be sure), so they should have 
been at somewhere more than 50%, but less than 100%, of their CNS O2 limit
at the beginning of their second dive.  

John

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