Gene Wirchenko wrote:

https://en.wikipedia.org/wiki/Gas_duster

"Air on the contrary, cannot be compressed into liquid at any
pressure since the critical temperatures of air components
(-146.9 C for nitrogen; -118.6 C for oxygen) are much beyond
normal handling temperatures.

What do divers breathe then?

[snip]

Sincerely,

Gene Wirchenko

The air in their tanks is compressed, but it is not a liquid.
As a result, the tanks don't hold very much.

If you can fill a tank with a liquid form, it can expand to
quite a few liters of gas. The critical temperature decides
whether that is possible or not. There is a table here, showing
the gases that are easy to do.

https://en.wikipedia.org/wiki/Critic...rmodynamics%29

"Cagniard showed that CO2 could be liquefied
at 31°C at a pressure of 73 atm, but not at
a slightly higher temperature, even under
pressures as high as 3,000 atm."

When divers go to more extreme depths, the tanks also
include Helium. The third link below includes quite a bit
of detail, including a list of unfortunate accidents
(people dying trying to set records).

https://en.wikipedia.org/wiki/Heliox

"Heliox is also used in saturation diving"

https://en.wikipedia.org/wiki/Saturation_diving

...the risk of decompression sickness ("the bends")

https://en.wikipedia.org/wiki/Trimix...eathing_gas%29

"The helium is included as a substitute for some of
the nitrogen, to reduce the narcotic effect of the
breathing gas at depth."

When a diver does cavern diving, they can become disoriented
and never make it back to the surface. And that's just from
breathing what is in the tank, and not the surroundings.
What can be especially bad, is if one diver freaks out
and attacks another diver trying to return him to the surface.

For some reason, the idea of diving never attracted me.
Too many stories. Too many details to remember. Diving to the
bottom of the pool at the YMCA was enough challenge for me :-)

Paul