Its high toxicity arises by the action of the phosgene on the proteins in the pulmonary alveoli which are the site of gas exchange: their damage disrupts the blood-air barrier causing suffocation.
Its high toxicity arises, not from hydrogen chloride released by hydrolysis, but by the action of the phosgene on the proteins in the pulmonary alveoli. The alveoli are the site of gas exchange, and their damage disrupts the blood-air barrier, causing suffocation.