With CO the issue is that it binds to haemoglobin and stays bound to it permanently. Only a small proportion of CO2 in the blood is bound to haemoglobin (~10% [

With CO the issue is that it binds to haemoglobin and stays bound to it permanently. Only a small proportion of CO2 in the blood is bound to haemoglobin (~10% [0]) so the real issue is that the O2 carrying capacity is reduced. As red blood cells are constantly being replaced limited exposure is not a long term issue, but this is a process that takes weeks. This means that someone with acute exposure cannot be helped with supplemental oxygen (or just being taken outside) unlike with CO2. CO2 in high concentrations causes issues through various mechanisms with a major one being that it impairs your ability to absorb O2 and other cellular disruption through increasing the pH of your blood [1]. This can cause unconsciousness in seconds at high concentrations and other potentially fatal impairments even at lower levels. So CO poisoning is worse as there's no (easy) therapy for it but it is still very possible to have fatal exposure to CO2 if you are not able to receive fresh air in a immediate time frame (minutes). There is also the general issue that confined spaces might be low on O2 as well, as described in this video on confined spaces in ships [2]. [0] https://www.ncbi.nlm.nih.gov/books/NBK532988/ https://www.ncbi.nlm.nih.gov/books/NBK532988/ [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380556/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380556/ [2] https://www.youtube.com/watch?v=uNVj_JpZia8 https://www.youtube.com/watch?v=uNVj_JpZia8