CO is dangerous because you <i>don&#x27;t</i> need to remove the O2 from a room to be lethal.<p>All the other gases cause asphyxiation by taking the place of oxygen in the air.  So once you leave the room, you&#x27;ll be fine.<p>CO is dangerous because it takes the place of oxygen in the blood and it has a stronger attraction to hemoglobin than oxygen.  So get enough CO in your blood and your organs suffocate, even if you are put in a pure O2 environment right away.