Choking agents inflict injury mainly on the respiratory tract—that is, they irritate the nose, throat, and especially the lungs. Victims typically inhale these agents, which cause the alveoli to secrete a constant flow of fluid into the lungs, essentially drowning the victim.

Examples of choking agents include:

• chlorine (Cl)
• phosgene (PG)
• diphosgene (DP)
• and chloropicrin (PS).

Choking agents were among the first agents produced in large quantities. During World War I both sides used them extensively. Because they sink into and fill depressions, they were well suited to trench warfare. Their successful use on the battlefield led to research and development programmes to create even more toxic and effective chemical weapons.