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Jason,

One thing I did not mention in my previous post -

Are you using 100% oxygen at the 20 and 10 ft stops???

There seems to be a situation where Haldanian models produce
inadequate tables when using nitrox for the shallow stops, and
produce fine tables when 100% oxygen is factored into the model
for the shallow stops. (Personal conversations with Bill Hamilton.)

Thus, using 80% oxygen at the shallower stops might be the problem.

If you are using 100% oxygen at the shallower stops, then "bumping up"
the times at those stops might make the difference.  Bill recommends
adding the 50ft stop times to the 20ft stop, and the 40ft stop times
to the 10ft stops in a way to increase the time on 100% oxygen that
will follow a predictable pattern on your dives.

If you are in a situation where you can adjust the "a" and "b"
values used by the program (if it is based on Buhlmann), then making
the values for the shorter halftime compartments more conservative will
produce deeper first stops, with very little effect on the shallower
stops.

Another way to make the profiles more conservative is to "fudge"
the inert gas values on the decom side of the program.  All the
programs that "fudge" the inert gas values only do this on the dive
side of the profile, not on the decom side.  Thus, manually entering
higher inert gas concentrations for the decom stops will more closely
approximate what the lungs see (the programs assume that when you tell
it that you have done a gas switch, that there is an instantaneous switch
at the alveolar level, which just isn't true.  Try telling the program 
that you are breathing 95% oxygen or 90% oxygen during the stops where
you are using 100% (and use 5% N2 and 5% He for the inert gas values
at those stops) will also make the profiles more conservative.

Hope this helps -

John
Submariner Research, Ltd.
(johncrea@de*.co*) 

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