[julie_m]

Carbon dioxide is heavier than air; so if you are standing up and aiming the extinguisher down, you won't be breathing much of it in. Even if you did, you'd be fine as soon as you brothe some "ordinary" (i.e., with 20% oxygen in it) air. Carbon monoxide is about the same density as air and also binds to haemoglobin, so your blood's oxygen-carrying capacity is reduced even after you get into fresh air -- urgent medical treatment is required in cases of heavy exposure to CO.

Carbon monoxide is also inflammable (the blue part of a carbon-based fuel flame is where the carbon atoms are acquiring their second oxygen, after picking up the first one in the redder part of the flame; soot is unreacted carbon, and serves to indicate that there is not enough oxygen even to partially oxidise all the carbon), so definitely would not be used in a fire extinguisher!