I had to idea how fast the O2 is depleted in some of the closed spaces (made of steel).

In closed containment, the time taken for oxygen level to fall to 19.5%, 10% and 6% at 10°C were 1.45, 18.08 and 25.3 h respectively whilst at 23°C the times were 0.3, 1.56 and 2.41 respectively.