International law has recorded a prohibition on the use of asphyxiating, poisonous or other gases in armed conflict since 1899, with the adoption of the Hague Declaration concerning asphyxiating gases. The treaty of Versailles, adopted at the end of the First World War, also contained a similar prohibition, as did the Geneva Protocol of 1925, which extended the prohibition to include bacteriological agents. The prohibition against the use of asphyxiating, poisonous or other gases in warfare is also reflected in the 1993 Chemical Weapons Convention (which prohibits all weapons which injure through the use of the asphyxiating, toxic, irritant, paralysing, growth-regulating, anti-lubricating or catalytic properties of a chemical, whether in its solid, liquid or gaseous state).
See also: Means of warfare; Weapons; Conventional weapons; Conduct of hostilities; Biological or bacteriological weapons; Chemical Weapons;