Phosgene is a highly toxic, colorless gas with a suffocating odor, primarily produced by the reaction of carbon monoxide and chlorine. Historically, it was used as a chemical weapon during World War I due to its lethal effects on the respiratory system. In modern times, phosgene is mainly used industrially in the production of plastics, pesticides, and pharmaceuticals. Exposure to phosgene can cause severe lung damage and is potentially fatal. While not a cybersecurity threat, phosgene is relevant to physical and chemical security, emphasizing the importance of proper handling, storage, and monitoring to prevent accidental or intentional release.