Shafts can be sunk like those of a coal mine next to shelters, where breaking through to the air within can be possible. Keeping air pressure will prevent it filling with water & enable expulsion or compression of carbon dioxide by creating a vacuum, which is also the method of using oxygen tanks.
It is also possible to pressurise the air in the shaft to make an enormous air tank.
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I am a servant of God of the whole world & I am proving that I am the only sensible choice to reign.
