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Hi Dan,
As I said, I have no experience whatsoever with semi-closed rebreathers,
so most of my comments were focused on fully-closed systems. I agree that
the risk of hypoxia is probably much less of a concern on most semi-closed
designs than it is on fully-closed systems ('though I'm not yet convinced
it is a non-issue), and I am sure the risk differs from design to design.
There is still the concern of hypercapnia, which I didn't even go into,
and loop floods and so on. I realize that these problems are more
self-evident (in general) than hypoxia or oxygen toxicity, but they still
require some training time. I have to say I certainly wouldn't be
comfortable making my first rebreather dive to 90 feet, and I doubt I'd
want to do any decompression diving with a semi-closed rebreather (perhaps
I'd change my mind after I had some experience with it), but without more
knowledge and experience with these different units, I'm not really in a
position to comment either way.
> survive in a pool by themselves, and probably on an easy ocean dive. With
> the rebreather (BMD, Odyssey or other similar unit)MANY easy dives will have
> to be undertaken to develop new reflexes, just like the new scuba diver.
> Again, I think without an instructor along, a pony bottle might make a great
> safety move. With the weight and bulk of the units, the tiny bit of drag
> you'd add would be negligable. Since you could'nt pass out from hypoxia, the
> out of air failure would be simple to compensate for. And once you became
> proficient after 150 or 200 dives, you could leave behind your training
> wheels(pony).
>
> So what do you think ?
You have more experience with semi-closed diving than I do, so I'm more
interested in what your opinions are. When you refer to the pony bottle,
would this be the only means of OC bailout, or just a supplementary one? I
think you would always want an open circuit route to the surface on any
dive in the event of a non-recoverable loop flood. It seems to me that
limiting OC bailout to onboard cylinders would be dangerous if a problem
occurred near the end of the dive.
I have a question. If I understand the compound bellows principle, the
purged gas is contained within a bellows that is inside the main
counterlung, correct? If so, what happens when there is a rupture in the
inner bellows membrane? Is it possible that considerable quantities of
gas bypasses the exaust system?
Thanks for your input.
Aloha,
Rich
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