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[–] lemon11 0 points 2 points (+2|-0) ago  (edited ago)

http://infogalactic.com/info/Carbon_dioxide#Toxicity

CO2 is an asphyxiant gas and not classified as toxic or harmful [...]. In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy and give the lungs a stuffy feeling. Concentrations of 7% to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour. [...]

Because it is heavier than air, in locations where the gas seeps from the ground (due to sub-surface volcanic or geothermal activity) in relatively high concentrations, without the dispersing effects of wind, it can collect in sheltered/pocketed locations below average ground level, causing animals located therein to be suffocated.

Summary: yes, especially for the short.

Edit: By the way, this is why you don't want those "Climate Change" CO2 sequestration tanks anywhere, especially on land in cities like they have been suggested. They are deadly.

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[–] KingChem 0 points 2 points (+2|-0) ago 

Because CO2 is has a higher density a 10% by mass would likely be enough to be a simple asphyxiant. Fortunately we measure CO2 in ppb.