It's a sealed vessel. You don't take very much air; it's a closed loop and you use a co2 scrubber -- the air gets reused. They only had

It's not that they "run out of air" so much as they "run out of scrubber".

This is also what rebreather divers do to allow them to stay underwater for very long periods of time.

Honestly they're dead from hypothermia long before they run out of scrubber. How long can you last at 5C in your normal clothes?