These materials include carbon monoxide and metal carbonyls that readily decompose to produce carbon monoxide (C09-A001). They are first generation warfare agents that were evaluated during World War I but largely abandoned because of the difficulty delivering an effective concentration of the agent. Between World War I and II, metal carbonyls were added to the fuelsofflameweapons (i.e., flamethrowers) asameansofproducinghigh levels of toxic carbon monoxide to augment their incendiary capabilities in situations involving soldiers occupying confined spaces such as caves and bunkers. Although this class of agents is considered obsolete on the modern battlefield, they are

still considered a significant threat as potential improvised weapons that could be utilized in urban warfare. They are commercially available but are relatively difficult to disperse over a large area.