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How was phosgene used during World War I?

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A labeled diagram of the chlorine element from the periodic table shows its atomic number 17, symbol Cl, electron configuration, and atomic weight range. The box is shaded green to indicate chlorine is a halogen, with icons for orthorhombic crystal structure, gas state at room temperature, and strong acidity. A key explains the icons and colors used. — chlorine Properties of chlorine.

During World War I, phosgene was employed as a lethal chemical weapon by both German and Allied forces. It was used either in its pure form or mixed with chlorine to be released as a gas cloud against enemy troops.12

As a choking agent, phosgene caused severe lung injury through inhalation, often with a delayed effect that could take several hours to manifest. It was particularly devastating, accounting for approximately 80 percent of all deaths attributed to chemical weapons during the conflict. While the initial use of gas clouds—such as the chlorine attack at Ypres—created tactical breaches, the subsequent development of gas masks and other protective measures eventually limited the strategic impact of these agents.21

The use of such indiscriminate and cruel weapons in warfare is a profound violation of fundamental ethical principles, which demand the protection of human life and the rejection of methods that cause unnecessary suffering and mass casualties.