An
asphyxiant gas is a nontoxic or minimally toxic
gas which reduces or displaces the normal
oxygen concentration in breathing
air. Breathing of oxygen-depleted air can lead to death by
asphyxiation (suffocation). Because asphyxiant gases are relatively
inert and odorless, their presence in high concentration may not be noticed, except in the case of
carbon dioxide (
hypercapnia).