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On Sun, 23 Nov 1997, John Dunk wrote:
> Would someone explain' the "fantasy" of holding an accelerated ppo2
> on a rebreather throughout a deco ' and why it's a fantasy?Are we
> talking tox here or what?And how does 80/20 supposedly help divers
> with poor buoyancy control? Hope I didn't come inb too late on this
> one. Also, someone mind listing the claimed benefits of 80/2?.
> Thanks
I have to agree on the point about rebreathers, particularly
closed-circuit rebreathers. If you purge a couple of times and
shut off the diluent add valve, you have a 100% o2 rebreather.
The amount of N2 that's being offgassed into the loop is
inconsequential.
80% "helps" (if such a word is appropriate) a diver with
poor bouyancy skills by not putting them in the rapid
tox zone at 25 or 30ft.
The actual benefits of 80/20 (besides the above) are nil.
The poorly thought out reasons for use are:
[1] The tox-depth relation thing, as noted. And I *do*
believe this has a place in training, as long as it
is explained as such. But if the student doesn't have
their bouyancy under control at the end of training,
the instructor has done a very bad job. Or the student
is an idiot, in which case, they shouldn't have been
certified.
[2] You run less tox risk with 80/20, as calculated by
the NOAA "CNS clock" values. This thinking simply reflects
a lack of education. As noted in previous posts, air-breaks
will extend your real tox probability by 50% or more.
-WIll
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