Keith Hughes writes:

When you do the math, it just isn't a problem when using any reasonable
amounts, and with only normal ventilation (which should *always* be
ensured under *any* use conditions).

Quite so.

A restaurant soda fountain typically has multiple 20 lb CO2 tanks sitting
around. If these were to leak out rapidly from a burst hose, which happens
frequently, there is no hazard to personnel.

A 20 lb CO2 fire extinguisher discharged indoors does not present an
asphyxiation hazard.