On Mon, 7 Jan 2002 23:21:46 +0800, J.M. Vitoux
<[log in to unmask]> wrote:

>Steven Catron wrote:
>
>> ----- Original Message -----
>> From: "Bjorn Vang Jensen" <[log in to unmask]>
>> > > One computer sets itself to a mix that totals more than 100 ??? Why ?

In the name of protecting fools on the one hand, and at the risk of KILLING
the same fools on the other, by FOOLING around with the algorithm!


>> > > - And why is 50% oxygen more conservative ?
>> In terms of oxygen exposure, wouldn't using the highest 02 setting be
>> the most conservative?
>
>In terms of O2 Toxicity yes. In terms on nitrogen loading definitely not.

The latter leaves the door WIDE OPEN for divers to get bent doing
repetitive dives on EANx, even on EAN36.

That was the kind of stupidity by UWATEC in the prototype Aladin Nitrox
computer (leaving the O2 setting at 36 during SI of EAN36, giving divers
the erroneous impression that s/he is offgassing MUCH faster than s/he
actually is, during SI), without REALIZING the rapidly increasing risk
of betting severely bent when the computer says it's "ok".

The lame excuse by those who put up with the fake 50% O2 setting is
usually that O2 TOX can kill instantly, while getting bent may not.

A slow death of being a quadruplegic in a DCI II hit may be worse than
a quick death or just a convulsion caused by the O2 clock, IMO.  But
that's beside the point.  The point is that there is ABSOLUTELY NO REASON
for any divecomp manufacturer to tweak and fool around with a computer
by deliberating putting in inadmissible settings that fools everyone!
For one thing, the decompression models (algorithms) have NEVER been
shown to be valid when the decomposition of air can exceed 100%.


>Your remark had me re-read Lee's post under a new light. If indeed, the
>computer by default sets Oxygen = 50% to track O2 toxicity/exposure and at
>the same time Nitrogen = 79% (obviously a fictive mix) to track loading, it
>results in the most conservative model (assuming that 50% is the maximum
>setting).
>
>Jean-Marc

The "most conservative" would be setting O2 at 100%.  Any manufacturer
stupid enough to allow a total "percent" setting to exceed 100% is smart
enough (takes about 2 brain cells) to allow a 100% O2 setting.

It's the LEAST conservative if you want to avoid getting BENT.

Even the UWATEC algorithm (which had since been declared "defective")
of leaving the O2 setting as set (rather than automatically changing it
to 21% during SI) was bad enough!  I had the DATA (both under lab
conditions and during an actual liveaboard on the CAIV) to prove in
court how DANGEROUS that was, for Uwatec not to have recalled those
early models (pre-1996) or admitted them being defective (by notifying
dive shops that well UWATEC Aladin Nitrox computers) until circa 2000.


It's FOOLISH for any computer manufacturer to deviate from the REAL
setting, in the name of "protecting fools".

It's FOOLISH for any computer user to use such a product not realizing
how DANGEROUS it is at the other end of the spectrum, N2 overload by
using fake and wrong ACCELERATED offgassing rate.  If you want to be
aggressive or conservative, use the computer between your ears to do
the tweaking!

Just use the Uwatec Nitrox Pro like Bjorn, myself, and many other divers
who don't NEED to treated as fools.  You set your EANx.  At surface
interval, it automatically resets to 21% (air), and reverts back to
EANx unless you re-set it for the next dive.  SIMPLE.  NO FOOLING.

As the old saying goes, "nothing is foolproof".  The fools will always
find a way.

No follow-up by me on this subject any time in the near future.  Old
stuff.  Been there many times before.

BTW, you don't have to be a FOOL to be CRAZY.  :-)  I highly recommend
it to anyone to see the film or read the book "A Beautiful Mind".   :-)

-- Bob.