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Trimix Algorithms

I+ve got one major concern when it comes to table predictions and use of
trimix. What about synergism? Ideally speaking each inert gas follows its
own m-values. In practice if one gas starts to go out of solution it drags
the other one with it. It+s obvious that one can take more of a combination
of inert gases than of either gas alone. 3 bars of helium + 3 bars of
nitrogen are less prone to bubble than 6 bars of either inert gas. But, I
don+t think it+s safe to assume that no synergism exists and calculate the
two as completely independent. For short dives it should be a safe overkill
to regard all inert gas as helium; that is: include nitrogen as helium, not
skip it. I+m not sure how the various users of trimix assess appropriate
decompression profiles and would like to get some input.

The switching between nitrox mixes is not controversial since one is
basically dealing with various concentrations of one and the same inert
gas. The same goes for switching between heliox mixes. While it+s obviously
 productive to break down inert gas into two and/or to switch from one to
the other,- who can say for sure what it+s really worth? Good air and
heliox tables are available and either can be used according to the EAD /
equivalent table depth principle. If one dives a trimix and either makes
his own calculations or employs one of the computerized tables, are the two
gases assumed to be totally independent?


Hans P. Roverud

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