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On Tuesday, December 12, 2000 10:27 AM, Hugh Huntzinger wrote:

(snip)
> FWIW, the "record" for open circuit air scuba is roughly ~525fsw by Dr.
Dan
> Manion (who later bent himself pretty good, but that's another story).
The
> ppO2 for this dive would have been ~10x the conventionally recommended
> limits (1.4 to 1.6; YMMV).

It's always seemed to me that there's no point to deep air records.  Going
deep for its own sake is a meangless exercise unless it's to push the limits
of scientific understanding or has, as its purpose, a specific
mission-oriented task.

When, in 1915, the U. S. Submarine F-4 sank off of Hawaii, in 304 feet, US
Navy Diver Frank Crilley reached the submarine in a dive that has rarely if
ever been equalled by a helmet diver breathing compressed air.  In the
'Twenties, experiments with helium showed that it was a far more beneficial
gas for diving.  It's been in regular use for nigh on seventy years in
commercial and military diving and - with reduced oxygen levels to maintain
'safe' PPO2's - helped to carry working divers deeper than air ever could.

It just seems to have taken an inordinate length of time for helium use to
percolate through to the recreational market!  :-)

(snip)
> So while I've been deeper, I personally consider ~110fsw to be my
pragmatic
> maximum operational depth on air.  This is the depth at which that I
really
> noticed that my UW camera has become noticeably "hard" to use.   That
> "hardness" really is narcosis impairment and I guess that you can say that
I
> carry a "Narcosis testing kit" with me :-)  I really do find it surprising
> just how "good" I can feel immediately prior to pulling the camera up to
> compose a shot...it really reveals just how insidious it is.

Indeed it is.  The reason for deep air diving deaths may well be oxygen
toxicity - but the chances are that it's caused by the diver's inability to
think rationally and sensibly due to an excess of nitrogen.

Strike