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>Dan, you still didn't answer my question about what is not safe about
>the "other" rebreathers, including our PRISM II.
>
>Dan Volker wrote:
>
>>Wrong Dennis!
>> The BMD had a hypoxic event, not the RBC, and the BMD had it because
>> the instructor wanted to let a student...
>
>Dan, we heard two divers went hypoxic in the Miami area on a BMD and
>that's why it was pulled from the market. You know any details?
Mike,
First, let me say once more, RBC is not BMD---they are VERY different, like
Cochran and Uwatek. I have not been following BMD training in Miami, though
I will check in to this for you. The way a BMD works, a hypoxic event would
almost have to be diver error in using air instead of nitrox as gas supply.
But without checking I can't contribute much on this.
>
>Re the RBC not having working units at Tek/DEMA, I understand and
>sympathize about the shortage of working units when you're supposed
>to be in production. As is all too frequently said, "Been there,
>done that, won't do it again."
>
>>The handouts which you must have seen clearly showed the enormous
>>difference in safety margins.
>
>Nope. Didn't get any. All I have is what was downloaded. Why don't
>you publish the handouts here? Downloaded stuff didn't show "the
>enormous difference".
Once I catch up in my work (put off through Tek and DEMA), I'll visit the
RBC guys and get more specifics coded and placed on the web site. And since
this is a freebie, it will have to wait a week or so until I can free up the
time. This thread alone is eating up my schedule, and I'm sure yours as well!
>
>>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.
>
>So does this mean that if electronics is added to the Odyssey it
>suddenly becomes unsafe? What if there existed a rebreather with
>primary electronics control, but if the electronics crashed was
>"safer" than the Odyssey?
If you created a mechanical system with the electronics as extra warnings,
that would interest me a lot. My favorite anology right now is the BC anology.
The RBC is more like a BC than the highly electronic units are. I have an
old Seaquest Explorer BC with over 10,000 dives on it. Its not even what you
would call a technical quality BC, but it's mechanical system is so simple,
it is very reliable. If I were to acquire an electronic BC, that added or
removed air bladder volume electronically, now I would have batteries to
worry about , shorts to cause failure, and electric motor failure.
Lets say it had a electronics in it to automatically detect if I was
neutral or not, and it would automatically inflate or deflate just enough to
regain neutral bouyancy. While this would be very cool if it was "failsafe",
few of us would be comfortable at the potential risk of the unit going
haywire and blowing us up to the surface, or any one of a half a dozen other
problems this new electronic BC could cause. Of course, we could add a huge
emergency dump valve (mechanical) and a secondary mechanical inflation
bladder, but the convolutions are becoming extreme. Someday, someone
probably will make one of these, and with Cochran's edge in elctronic
technology, it will probably be you guys. But today, right now, ALL
electronics used in diving is still prone to more failure than mechanical
systems.
And if we take a vote right now for the traditional mechanical BC,
or the conceptual "Electronic BC", I believe most divers on the tech list
will opt for the superior reliability of the mechanical one. But all of us
would be thrilled if some techno-breakthrough in the next few years changes
the reliability equation.
Of course I use a dive computer. But I don't rely on it. Divers need to be
computer assisted, not computer dependent. Your company may very well be
leading the way towards the perfect electronics of tomorrow, but the
electronic equipment "used" today needs to be for assistance. If dependance
is on an electronic sensor or other electrical system, I would be nervous.
Where you suggest having both mechanical control, and electronic backup, I
think you will have the ideal system.
>>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.
>
>Dan, can't believe you said that. A task-loaded diver could easily
>overlook those symptoms. Furthermore, the huffing and puffing method
>only works in shallower water.
OK Mike, you do have a good point here about tolerance to CO2/O2 at depth.
This is an area where as a diver, I know I have to swim at an even, steady
pace at 280 feet, and not exert. The times I have had to exert, I have felt
the sudden CO2 buildup, and felt the difficulty in ridding my system of it.
In the old days, when I would have been doing this on air, the threat of O2
tox was increased enormously by this large buildup of CO2, but still, I
would always feel the increased CO2 levels, even with the diminished mental
acuity that 280 ft on air brings. Now I am willing to agree with you an
extra warning system would be desirable here, particularly when running as
high a PO2 as I was when I did these 280 ft dives on air. Now that I am
"enlightened" by the tri-mix god, my PO2's on the same 280 ft profile are
low enough so that the "Real Danger" would probably not be instant blackout
without warning. With the lower PO2's of trimix for this depth, the diver
who is "forced" to exert will still build a high CO2 level, but will begin
breathing very heavily, and know it...he/she will also be aware that either
they must slow down, or if on a rebreather, and not exerting, assume a
scrubber failure. The main problem with large CO2 buildup at 280 feet is a
decreased ability by the body to remove CO2 at this depth. This is one of
the reasons that all tech divers at deeper depths should be close to elite
level aerobic athletes, to have the best internal gas exchange system
possible.{ This is ONE of MANY reasons why the WKPP divers are among the
best deep exploration divers --they make use of an optimal cardiovascular
system.} And awareness of high PO2 levels will mean the diver should pop up
about 50-80 feet (at least) higher in the water collumn if the exertion gets
to be too severe to remove a dramatically high level of CO2. Of course cave
divers will not have this option, so they need better cardiovascular
systems, and better awareness of their exertion and CO2 levels.
>
>
>That's enough for now. Got to go do some real work.
>Mike C.
ditto.
Regards,
Dan
>
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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