A little off the rebreather topic, but.....
Just got a neat box in the mail. It's a cryogenic (liquid
air) SCUBA. Ought to be good for many hours and it's smaller than a
rebreather (and less complex to use, as it's really just an open circuit
system fed by the gaseous boil-off of liquid air). I'm planning on mixing my
own "air" from LOX (liquid
oxygen) and liquid nitrogen. This was I can make nitrox in
any percent desired. Liquid air turns richer in 02 as it boils off over
time, as the temperature for boil-off is lower for 02 than nitrogen.
The genesis of the system is that in the 1960's Jim
Woodberry, who was working for NASA, built a spin-of system from the system
he was engineering for Apollo and this system was marketed by Jordan Klein
as the "Mako" cryogenic diving system. It was reviewed in Skin Diver (I have
the original articles). Just after that was announced, the Russians copied
it almost exactly as the "Kryolung". They only built a few, and it's one of
these that I managed to obtain.
Interestingly, Jim Woodberry was Diving Officer at the
Florida Institute of Technology when I took my degree there. I remember
talking to him about the cryogenic systems, ad he taught my hyperbaric
physiology courses. Small world!