The problem with CO is that there actually is no safe limit and one never actually recovers from inhaling it… yes there is the ‘official’ safe limit but the reality is that the more you ingest, the more damage is done….and any damage done is permanent. So, inhale a little and do a little permanent damage, inhale a lot and do a lot of damage.
Where would it come from in a mall?
What permanent damage? CO binds permanently to hemoglobin, but as red cells are replaced, the carboxyhemoglobin is gotten rid of, so what permanent damage are you talking about?
First, there is always a "safe limit" for anything. If you don't understand that, you don't understand the "fineness" of the granularity of matter.
Second, small amounts of CO will NOT do any permanent damage to the human body. Larger amounts may. (I would call death permanent damage. Brain damage is also possible but certainly NOT inevitable.)
Third, the effects of CO are not cumulative over large spans of time. They may be cumulative over short spans of time.
Fourth, the binding of CO to hemoglobin IS a reversible reaction, but it does take a while for it to occur.
CO is very toxic. If I recall correctly, the lethal dose 50% (LD50) is 1% for one minute.