Much to my chagrin, I humbly stand corrected on my prior statement concerning the relative weights of air and carbon monoxide (CO)!  CO is lighter than air, ie rises.  (Pets everywhere can breathe a collective sigh of relief) ... CO is a by-product of incomplete combustion, however, carbon dioxide (CO2) is also a by-product ... and CO2 is heavier than air (Pets everywhere pay attention now).  And unless you're a plant or alien, breathing too much CO2 is definitely not a healthy thing to do.

Egg wiping complete, face still a bit sticky...

Ken Hartz