Although phosgene has not been deployed as a chemical weapon since 1918, its continued use in common industrial processes, such as dye or plastic manufacturing, makes it a potential industrial hazard today. Phosgene gas has the appearance of a white cloud and the characteristic odor of newly mown hay. Odor alone is insufficient for the detection of phosgene exposure, since toxic exposures may occur at concentrations below the olfactory threshold. Although phosgene is one of the most volatile chemical warfare agents, its density is greater than air, and it tends to accumulate in low areas. Phosgene exerts a direct toxic effect on the respiratory tract, causing extensive cellular damage to the alveolar-capillary membrane.
Phosgene reacts with intraalveolar water to form hydrochloric acid, which injures the alveoli.
The clinical effects of phosgene are dose dependent. At low concentrations, victims may complain only of a mild cough, dyspnea, and chest discomfort. At moderate concentrations, they also may complain of tearing. At high concentrations, victims rapidly develop noncardiogenic pulmonary edema within 2-6 hours of exposure, producing a clinical picture similar to adult respiratory distress syndrome. Laryngospasm also occurs at higher concentrations, which in turn may cause sudden death.