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Jody Svendsen writes:
> Dave Story writes:
> > My understanding of Buehlmann's Decompression/Decompression Illness
> > (and physics) is that the gases diffuse independently. Therefore,
> > although He enters the body 2.65 times as fast as N2, it also
> > offgasses 2.65 times as fast. With this in mind, I can't see the
> > sense in your last sentence.
>
> That is correct, He in-gasses AND offgasses at 2.65 times the rate of N2.
> The problem is that because helium ingasses more rapidly, it tends to fill
> the very slow tissues to the point where they require decompression.
> Decompresing the slow tissues takes a long time because their M-values are
> very low and it is difficult to get a good pressure gradient to push the
> gas out of the tissues, particuarly if you are not decompressing on 100%
> oxygen. As an example, using bottom gas for decompression, a dive on
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> normoxic Heliox to 200 feet for 20 mins requires 687 mins of decompression
> while a dive on Air akes only 38 mins.
Ah, I see our differences now. Why would one use trimix for
decompression? It's far too expensive! Even using nitrox or air, you
have 0% He in your decompression mix, and your offgassing ought to
progress quickly.
Given that the N2 is ongassing more slowly than the He is offgassing,
your decompression -- on a 0% He deco mix -- should be faster, no?
Cheers,
David Story NAUI AI Z9588, PADI DM 43922, EMT
story@be*.wp*.sg*.co* Better diving through inflatables.
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