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Marv writes:
>
> Is the floor on air really 185 feet [ppO2 ~ 1.4]?

It depends on what your criteria is.   From oxygen toxicity, 1.4 is pretty
safe, so the answer is basically no.  But this is very simplistic and
ignores the hazards from Nitrogen Narcosis and CO2 buildup which really are
the issues for air mixes.


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).

You can also refer to a decompression chamber mix-up that was experienced by
Richard Pyle, where he was put on pure O2 at ~8ATM (if I recall correctly)
for a relatively short duration.

What's common in both of these are events where someone survived very high
ppO2 exposures.   All that this is really telling us is that some % of a
population can survive such (short duration) exposures, By analogy, there
are people who have survived the poison of the blue ring octopus, as well as
there have been people who have survived skydiving accident falls of 5000+
ft.

Of course, there's also more people who have died from such exposures, but
that's the nature of statistics of highly hazardous environments.   But
since you can also get narc'ed at <100fsw and end up killing yourself in
what would be considered a "depth-related/contributing" incident, it again
comes back to what you are choosing as your criteria.  Risk, safety margins,
all that.


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.


-Hugh