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The following is excerpted from a letter I received from Bret Gilliam
today:

"1. The Navy and NOAA guidelines for oxygen exposures have proven to be
excellent baselines for all diving populations over the years and
regardless of idiosyncratic exceptions, most professionals are confident
in recommending these exposures. In fact, there has never been a
documented case of an in-water oxygen toxicity hit on a sport diver (in
any application) if he was within these prescribed limits.

2. The Navy/NOAA guidelines were developed for "working divers"
specifically. As such, the breathing rate, metabolic consumption, etc.
are presumed to be well in excess of the typical sport diver who is,
essentially "at rest" for most underwater activities. Of course, some
divers such as wreck divers or heavily burdened tech divers may approach
"working diver " ranges but this is not the norm and such divers are
advised to make an individual, personal decision to adjust his exposure
either by partial pressure or time limit. But for a sport nitrox diver
under typical conditions and exertion rates, 1.6 ATA is perfectly
acceptable as a baseline recommendation.

3. There is little in life that is an exact science especially when
dealing with varying human physiological parameters for diving. In my
opinion, based upon almost thirty years of intense practical diving
experience, the Navy/NOAA exposures are suitably conservative for all
divers and particularly the general sport population. References to the
theoretical "probability" factors is fine for academic discussion but the
hard facts are that divers are not having any problems in their use of
nitrox mixtures within the limits referred.

4. Neither TDI, nor any other tech agency that I am aware of, has
recommended that reductions from 1.6 ATA are necessary for use with nitrox
within sport ranges. Reductions are noted for consideration in deeper
diving primarily with trimix or heliox where there are other factors to
consider such as the burden of the equipment package the diver carries
etc. Since the tech diver is planning to manage both oxygen and narcosis
tolerances, it is a relatively simple to make adjustments to mix as part
of the pre-dive plan."

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