Imagine an abandoned mining base or other facility still has a breathable atmosphere in it for some reason. At what point will the air inside the base become too cold to inhale for more than a few seconds? According to a Canadian (they should know about the cold) source only emergency work should be done at temperatures of -43C (-45F) for a four hour shift. Not to say that isn't cold but it is obviously safe enough. I want it to be just cold enough not to kill them right away. I would guestimate that the real limit would be closer to -100 degrees or lower but I have failed to find any evidence of this?