Incapacitation from carbon monoxide poisoning is related to activity level at any CO conc. - time product (Ct). At acutely high CO levels, it is not so important how high the CO concentration is - if it is high enough to cause incapacitation, death will automatically follow once escape is impossible.

The first four plots are taken from - Purser, D.A., Toxicity assessment of combustion products, from: Handbook of the Society of Fire Protection Engineering, DiNenno, P.J. et al., Ed., 2nd ed., 1995.