Discussing the  effects of breathing CO and CO2, it was said:
>If I recall correctly, the bond is permanent," in which CO bonds and thereby
kills a hemoglobin cell.  That is correct.

But with respect to CO2 concentrations,
>CO2 doesn't harm directly as CO does, but will displace all the
>oxygen in a confined space to the point you can suffocate."

I believe CO2 concentrations do not need to displace oxygen before
we are unable to breathe.  You can have plenty of oxygen left and
still fail from CO2 concentration.  To read about this mechanism,
use a search engine to read about this effect which I have seen
discussed in Space mission environment controls, underwater
"rebreather" equipment, and survivalist literature about designing
long term temporary habitats for surviving after an ecosystem
upsetting event like an atomic war or a significant space rock
hitting earth.  They all discuss chemically removing CO2 as an
absolute necessity long before lack of oxygen is a serious concern.

Peace,
John