What Happened to Cryogenic Scuba?

[Akimbo]

There were articles on Cryogenic (liquefied air) Scuba developed by Jim Woodberry in the June (page 22) & December (page 28) 1967 issues of Skin Diver Magazine. Basically, liquid air was stored in Dewar flasks and warmed into gaseous air for breathing. Skin Diver’s editor, Paul Tzimoulis, reported diving a prototype to 100’ and the inventor diving to 200’.

The December article indicated that Mako (the air compressor manufacturer) was weeks away from finalizing the design and shipping production units. That was the last word I ever found on the subject.

So what happened? Did they discover a concept flaw, decide it wasn’t marketable, couldn’t deal with the weight change in the days before BCs, or there was not enough patent protection to justify bringing it to market?

The advantages are that the liquid to gaseous conversion is ~1:815 versus ~1:234 for a 3,442 PSI bottle and the operating pressure is below 250 PSI. Among the disadvantages is a pressure gauge would not indicate remaining air.

[emoreira]

When I was in the SSI OWD course 4 years ago, I also asked to the instructor what about a liquid air tank. He knew nothing about it, but the only point we discussed was the need of a different and very expensive production plant to fill tanks.
Another point would be the cold air that the diver should breathe.

[fdog]

I've spent quite some time inside a HazMat Level A suit using a liquid air SCBA. It was great - nice cool air to breathe, it was not a sauna inside the suit - plus your suit time became determined by your bladder and how many munchies you zipped up with.

There was a lot of infrastructure to support the system that just doesn't exist in the regular world. Plus, you couldn't "store" the SCBA in a ready to us configuration, you had to fill it right before use.

As nice as such a system would be for diving, until someone bites the bullet and has a cheap cryogen distribution system, I can't see it happening. Plus I recall the N2 % would vary a bit with boil-off, that would be an issue for deco.


...didn't really answer the question, sorry - I have NFI as to why it went nowhere.


All the best, James

[Akimbo]

Cryogenic distribution is not that big a deal. Every decent size hospital and welding operation gets LOX and a lot of industries use LN2. Mako had storage up to 6 days in 1967. The cost of infrastructure is probably less for a dive shop than an HP system. Large capacity units lose very little/day.

All that was understood when these articles were written. It would be interesting to know why such a hyped project was so silently scuttled. Attached are scans from Skin Diver's December article.

[Akimbo]

…. He knew nothing about it, but the only point we discussed was the need of a different and very expensive production plant to fill tanks...

There are plenty of industrial gas plants around the country producing LOX and LN2 now. They deliver bulk liquid to distributors who sell to hospitals and industrial consumers. These same plants produce HP oxygen, nitrogen, and argon through the same cryogenic systems that produces the LOX and LN2.

All the dive shop would have to do is rent or buy two Dewar flasks for liquid Oxygen and Nitrogen to make any Nitrox mix or pure O2. Mixing is easier than for gaseous mixes than HP.

We had 500 gallon Dewars of LN2 delivered offshore for the Helium reclaim systems. As I recall, it was much less expensive than HP Nitrogen. We used it as a refrigerant for a system that would precipitate all the other gases out leaving only pure helium (and trace amounts of hydrogen that may have entered the system). It took a lot less to train someone to safely use it than to maintain HP compressor systems.

…. Another point would be the cold air that the diver should breathe.

As I understand it, it takes very little heat exchanger area to get the gas up to the water temperature. It might even be warmer than air in an HP cylinder at water temperature and expanded at the first stage.

[Lwang]

they probably got deco sickness and didn't know why, thinking it was due to the liquid air.

[Lwang]

Ignore, duplicate post.

[altaskier]

Given that the boiling point of oxygen is 90 Kelvin and nitrogen is 77 Kelvin, I would have thought that a cryogenic mixture of 21% oxygen and 79% nitrogen would lead to the following dive: first the oxygen boils off and you convulse from oxygen toxicity and die, and then the nitrogen boils off and you would die from hypoxia. I'd rather die zero times instead of two times during a dive...

Of course this is a simplification and one would have to consider the relative vapor pressures of nitrogen and oxygen at 90 Kelvin... but air is a mixture not a compound...

[Lwang]

i thought the boiling point being different would be the case if you just let the liquid boil off and breathe it, but the gizmo drains off the liquid into a narrow tube and raises that liquid's temperature via heat transfer with the surrounding water. It will have warmed enough to the point that both oxygen and nitrogen has already evaporated and are near ambient temperature.

The gizmo was probably too complicated that was trying to look for a problem to fix when there wasn't any. There is no need for a tank to hold more air than required for a single dive and this holds up to 5 hrs of air. One will hit NDL way before air runs out.

[Sat Diver]

Given that the boiling point of oxygen is 90 Kelvin and nitrogen is 77 Kelvin, I would have thought that a cryogenic mixture of 21% oxygen and 79% nitrogen would lead to the following dive: first the oxygen boils off and you convulse from oxygen toxicity and die, and then the nitrogen boils off and you would die from hypoxia. I'd rather die zero times instead of two times during a dive...

Of course this is a simplification and one would have to consider the relative vapor pressures of nitrogen and oxygen at 90 Kelvin... but air is a mixture not a compound...

These problems are not that difficult to solve from an engineering standpoint.
As Akimbo says, I'd be curious to know why it went under.