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> I have not been able to find in the IANTD materials statements
> regarding how the depths of repetitive dives should be ordered when
> nitrox is used on one or more of the dives.

I can't find that specific issue addressed anywhere in the IANTD
materials, either in the Nitrox Instructor's manual, or in the
Student Workbook. Most of the examples in the workbook tend to order the
dives according to decreasing EAD, though.

In particular, the new (1994) edition of the Student Workbook has a
sample problem in the "dive tables" section in which repetitive dives
are done to 90 FSW, on Air, EAN 32, and EAN 36 (in that order). This
seems to reinforce the idea of ordering the dives by decreasing EAD.

When I teach Nitrox, I normally take a rather conservative approach
on dive planning. I try to emphasize the physiological advantages of
Nitrox over the extended bottom time, and reinforce the following
rules for dive planning:

    1. Dive Nitrox as though it were air.
    2. Plan dives so that the deepest actual dive is first
       (i.e. use normal dive planning rules).
    3. In addition, plan dives so that the deepest EAD dives
       are first.

In most cases, this results in air dives being done ahead of mix
dives, especially on repetitive dives to the same or similar depths.

Some of you may not agree with this, but that's how I'm most
comfortable teaching the material (most of my students are purely
recreational divers, and have no interest in more technical
pursuits). I feel that this approach is safest, and is most
consistent with what they have already learned in their OW training
courses.

> The kicker comes in when the O2 CNS clock is added.  Now there is a
> balancing act between N2 loading and O2 CNS clock.

In most cases, for most divers doing recreational type no-stop dives,
the CNS clock is not that big of a concern. That doesn't mean that it
can be ignored of course, just that few recreational divers get into
situations where exposure is a problem. Under those conditions, I
think the N2 loading is the more important thing to worry about.

-JimG

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