the book im reading had a cavein and the main characters decided to dig deeper for fresh air.
no, they were saved by the S-teir elemental that caused the cave-in in the first place. litRPGs doing their thing.
Well, CO is lighter than air. Not a bad idea if carbon monoxide is the immediate threat
CO is 97% the weight of typical atmospheric mix, so yes it’s lighter, but by such a small difference that it spreads and fills a space evenly over a short period of time rather then starting at the ceiling and filling in the space downward.
Basically, going down to escape won’t work, you need to get away from the area of high concentration.