According to Jamie :
CO doesn't exactly suffocate you. You make it sound like you'd need there to
be more CO than oxygen in order for it to kill you. According to this, you
body will always use CO before oxygen when both are inhaled.

And yes - it can kill you very quickly.

Very small amounts of CO can kill you quickly.

"Near zero" CO emissions from cars can kill you if you're not ventilating
well enough. Starting a car in a closed garage and sitting in the
car to read a book is about the easiest and gentlest ways to die there is.

There are no "survival instincts" triggered by CO. CO2 triggers a
physiological reaction (you _know_ you're not getting enough
to breathe, because that's part of the active feedback of how your
breathing system works).

CO does not. It has no smell. You have no way of knowing it's happening
_unless_ it's accompanied by something else (like smoke). If you're
_expecting_ the smoke ("well, gosh darn it, there is a generator running
in the bathroom!"), well...

Your blood stream simply starts carrying less and less oxygen and you fall
asleep (if you aren't already). Then die.

More people died in the great ice storm from CO than any other cause.

Many of those were inadequately ventilated generators.

CO kills by preferentially binding to the haemoglobin in your red blood
cells _instead_ of O2, but your cells aren't interested in using CO.

It binds tightly enough that you do not get rid of it very fast.

Which is why a short exposure to CO can lead to a long recovery on pure
O2.

[In severe cases, they can resort to pure O2 in hyberbaric chambers. Above
about 30PSI, you don't _need_ haemoglobin in your blood stream to carry
enough O2 to stay alive long enough for the CO to eventually go away.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.