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I'm sure that many of us have heard Dan Volker from <rec.scuba> and
<techdiver> mention hyperoxic (sic) trimix as an alternative to air at
moderately deep depths.
 
Assuming an unlimited budget :-) and interest, its quite possible to dive
all sorts of stuff other than air when vacationing in the future.  Take the
following hypothetical example:
 
1st tank - some form of trimix.   Typical deep spike multilevel dive working
up the wall, etc.  Probably a bit deeper than 130fsw because the mix allows
it.
 
2nd tank - some form of EAN (36%, etc).   Typical long, shallow reef dive.
 
 
Obviously, such a morning of diving is going to be more complicated in dive
theory than the basic recreational diver doing similar profiles on air.
But with more and more advanced dive computers, its going to become easier
to do such profiles with less stringient planning (even if this isn't a
particularly wise idea, but that's another question).
 
 
Naturally, you need to track Nitrogen, O2 clock and He for the first dive.
 
But because the 2nd dive is He-free, once successfully finished the first
dive and surfaced (let alone any additional safety margin by the completion
of a reasonble Surface Interval), is whatever residual He relevant at all
for the second, Helium-free Nitrox dive?
 
Obviously, dive planning would be simpler if you could ignore the Helium at
this point.  The question is if you safely can.
 
 
Comments?
 
 
-hh