Uh! Makes you think. So the idea would be to have a lower underground room which you could “pump” out the gas?

Assuming energy is an issue, a passive pump might be able to be built through usage of a copper pipe by creating a thermosiphon (the exposed copper pipe outside would heat up creating hot air which would “siphon” the bottom air).

I guess the issue with living underground sre many: moisture, possible radon, water infiltration, pest, no good way of making a fire, etc…