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David Giddy wrote,
>
> >From: Jason Rogers <gasdive@sy*.DI*.oz*.au*>
> >
> >
> >I buy "Medical Grade" He,  There is also available "Diving Grade" which
> >contains 2% O2.  (Because of safety, In a commercial heliox diving situation
> >having "pure" gas onsite is dangerous.  If it is switched to the diver by
> >mistake then he would die before you had time to correct the situation.
> >2% means that the O2 level will support life at most of the depths that
> >heliox is used).  There is also "Laser Grade" which is fantasticly pure.
> >(and fantasticly expensive)  99.999% He or better.
>
> Last Friday, I went on a one day intro course on the Prism rebreather given
> by Peter Redey (He's touring Australia with it at present). During the
> course he mentioned the problems with pure He.
>
> According to him, the reason that diving He contains a small quantity of
> O2 is not so much to keep someone alive on, but to ensure that if they do
> breathe pure He by accident, then thay can be resucitated. Apparently pure
> He does something to the brain which prevents resucitation even if you get
> to them quickly with pure O2. However, with as little as 2% O2 in the
> mixture, the chances of resucitation are much better.
>
> Jason, does this tally with your knowledge of the commercial industry ?
>

Yes Exactly.  After you have fed the diver a pure inert gas he stops
being quite as entertaining over the comms.  The pure gas washes out
all the O2 from the blood, and when this near zero oxygen blood hits
the brain the diver dies.  This makes him *very* dead indeed, and
just about impossible to restart.  It isn't the He, it's that when
there is *no* O2, the lungs *remove* O2 from the blood.

Jason :)

Wellington St. Deep Diving Team

"Since then I never pay any attention to anything by 'experts'.  I
calculate everything myself."
                       Richard P. Feynman

"WHATEVER happens to you when you willingly go underwater is
COMPLETELY and ENTIRELY your own responsibility! If you cannot
accept this responsibility, stay out of the water!"

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