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Date: Wed, 24 Jan 1996 22:55:22 -0500
To: Mike Cochran <mcochran@ne*.co*>
From: dlv@ga*.ne* (Dan Volker)
Subject: Re: Availability of Rebreathers
Cc: techdiver@terra.net
Hi Mike,
The issue was and is the production of safe units. Odyssey has already put 
them in the field, and has delivered completed units ...unfortunately for 
Odyssey at TEK and DEMA, the shipment they had been planning on using for 
display was too late out of production. 
The handouts which you must have seen clearly showed the enormous difference 
in safety margins.
 

>RBC Odyssey sign was).  At Tek and DEMA all we saw was non-functional
>Odyssey shells (we peeked inside) at a couple of booths.  At the pool
>sessions, we had three PRISM IIs and took in more divers than all the
>other guys (Drager, CisLunar, Divex, and the CCR1000) combined.  The
>Odyssey was not there.
>
>It is important to me why you say the Odyssey is the only one that is
>'SAFE'.  What is not safe about the others, including our PRISM II?
>(One can disregard the CCR1000, it's an older military unit that, I
>think, is not around any more.)

Safety is superior in the Odyssey because it does not rely on electronics 
which will potentially fail, and in so doing allow a diver to become hypoxic 
should there be a gas addition failure.

>FYI, we downloaded the Odyssey pages that you suggested and there are
>a number of statements that are incorrect.  I don't want to get into
>that here unless you insist, but if you want to EMAIL, that's great.

I insist. What statements?

>
>Regards, Mike C
>
snip-

>Dan, no one asked US if we thought the Odyssey was the safest or best,
>and not having studied or dove one, I can't say.  IMHO, however, ANY
>rebreather without a PPO2 monitor is inherently not "SAFE".  How do
>you *REALLY* know what you're breathing (blind faith)?

Mike, the "safe" method of knowing your PO2s is computing the desired mix 
based on depth, and using these mixes.  I would NEVER trust my life to 
electronics ---electronic failures are far too common, even with good dive 
computers (I'm sure you know what I mean here Mike ;)
 


  Same goes for
>a CO2 monitor.  How do you *REALLY* know the scrubber is working
>*BEFORE* you pass out (CO2 is sneaky)?
Apparently you have never simulated hypercapnea. It is VERY apparent that 
your breathing rate is sharply elevated. CO2 is not really all that 
sneaky---as a human your breathing is controlled by CO2 levels---you are the 
most dependable CO2 sensor you can ever find.

  Furthermore, without a dive
>computer, the diver is in the lap-of-the-Gods regarding deco info
>because you don't *KNOW* what gas mix you are breathing and it changes
>based on a surprising number of variables in many rebreathers.

Mike, step back and think for a second. We are having this conversation on a 
technical diving list. People here dive multiple gases on typical dives. If 
you have come up with a dive computer that senses me starting with air, 
switching to tri-mix at 130 feet, tracks my nitrogen and helium saturation 
on my 275 foot dive, figures the offgassing as I return to 150 where I 
switch back to Nitrox , begins to figure counter diffusion and offgasing 
with this switch, alows an air break at 50 feet for 15 minutes, and then 
nitrox for next few stops, followed by  pure O2 at 10 feet----If you have 
come up with a computer that will do all this, how reliable is it, and how 
many of us do you expect will trust it...The best divers I know, the guys 
who go further and deeper into caves than ANYONE else, believe the ONLY safe 
way to do technical exposures is with a pre-calculated profile and a bottom 
timer and depth gauge....They don't trust ANY computer---why do you think 
that is?   

  One
>can argue about tables and fudge-factors and preset mass-flow
>controllers, etc. all day long, but if you don't have an on-line
>computer that computes deco info from the actual depth and *ACTUAL GAS
>MIX* you are breathing, one has to assume a worst-case scenario.
>
>FYI (based on info we have, maybe not current):

>similar to the BMD which was pulled from the market.  What is the
>difference between these two units?

There are very large differences between the two, and I'd be happy to 
discuss them with you after we finish with the information we have just now 
gone over.
>
>Dan, I don't mean to start (or contribute to) a flame war.  I'm just
>asking what I think are some reasonable questions based on this
>threads posts and responses.  If you would like to take your answers
>private, let me know, no problem.
>
>Kind Regards, Mike C


Mike, I actually like what you are doing with computer technology, and I 
think some day you will have the best on the market---presently you do have 
the best features, by a good margin, and an awesome computer for advanced 
recreational divers, but for tech diving the reliability issue prevents its 
use as anything but a novelty---not to mention we may frequently use three 
or more gas mixtures on a dive, this being beyond the scope of any  dive 
computer I have heard of. 
I don't want to get in to a conversation with you that will hurt your 
marketing, but I will respond with what I believe is the safest message for 
other people to hear. 
>--
>Send mail for the `techdiver' mailing list to `techdiver@terra.net'.
>Send subscription/archive requests to `techdiver-request@terra.net'.
>
>
Dan Volker
SOUTH FLORIDA DIVE JOURNAL
"The Internet magazine for Underwater Photography and mpeg Video"
http://www.florida.net/scuba/dive
407-683-3592

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