Apparently 14 K cooling is not used even up to 5N or 6N purity, commercial large-scale sources use various other tricks to remove the other gases. They do cool the input gas down to liquid nitrogen temperatures as one of the first steps.

My point is that there's "maximally efficient / profitable" versus "can be made available as an emergency alternative".

Cooling to 14 K isn't the cheapest option, but it has very low complexity. You can "simply" pressurise the source gas, cool it to room temperature through an ordinary heat exchanger, then allow it to expand. The only issue is that if you do this naively, the expansion nozzle will get clogged with ice.

Obviously, this wastes a lot of Helium, but we have lots of it. If what's needed is high purity Helium, then throwing away even 90% to get 10% that's 6N pure should be no problem for an industrial nation.

Damn, that's intense:

> If the scan room door is closed when a quench occurs and helium escapes into the scan room, the depletion of oxygen causes a critical increase in pressure in the room compared with the control area. This produces high pressure in the scan room, which may prevent opening of the door. If this should happen, the glass partition between the scan and control rooms should be broken to release the pressure. The scan room door can then be opened as usual and the patient evacuated. In such a case the patient should be immediately evacuated and evaluated for asphyxia, hypothermia and ruptured eardrums.