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Ian,

If tracking the uptake and elimination of 2 inert gases is "dodgy", then
it really does not matter wheither you dive with Trimix or with Heliox,
as in each case we have to track 2 inert gases as to uptake and elimination.

In the trimix case, we are tracking helium and nitrogen uptake and
elimination both due to the breathing gas, and due to the tissue
staturation with nitrogen at approx. 0.75bar.  Thus, some compartments
will be taking up both nitrogen and helium during the dive, some will
be taking up helium and eliminating nitrogen during various phases of
the dive, etc.

With a heliox dive, we must track the elimination of nitrogen during
the dive (again, we start the dive out with all compartments staturated
with 0.75bar nitrogen when we leave the surface), as well having to track
helium uptake and elimination.

As to trimix and DCS, the major projects (ie, Wakulla Springs; Sullivan
Sink/Emerald Sink; Eagles Nest; and DiPolder II) have had exemplary
safety records, with NO DCS reported.

However, trying to compare these safety records to the vast majority
of technical divers is more difficult, as we have a large number
of different tables in use, with different safety factors figured into
the tables.  Technical divers have developed DCS, but we have no
central clearing house to allow anykind of estimation of risk or 
incidence.

Hope this helps -

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

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