<P> In October 1914, German troops fired fragmentation shells filled with a chemical irritant against British positions at Neuve Chapelle, though the concentration achieved was so small that it too was barely noticed . None of the combatants considered the use of tear gas to be in conflict with the Hague Treaty of 1899, which prohibited the launching of projectiles containing asphyxiating or poisonous gas . </P> <P> The first instance of large - scale use of gas as a weapon was on 31 January 1915, when Germany fired 18,000 artillery shells containing liquid xylyl bromide tear gas on Russian positions on the Rawka River, west of Warsaw during the Battle of Bolimov . However, instead of vaporizing, the chemical froze and failed to have the desired effect . </P> <P> The first killing agent used by the German military was chlorine . Chlorine is a powerful irritant that can inflict damage to the eyes, nose, throat and lungs . At high concentrations and prolonged exposure it can cause death by asphyxiation . German chemical companies BASF, Hoechst and Bayer (which formed the IG Farben conglomerate in 1925) had been producing chlorine as a by - product of their dye manufacturing . In cooperation with Fritz Haber of the Kaiser Wilhelm Institute for Chemistry in Berlin, they began developing methods of discharging chlorine gas against enemy trenches . </P> <P> According to the fieldpost letter of Major Karl von Zingler, the first chlorine gas attack by German forces took place before 2 January 1915: "In other war theaters it does not go better and it has been said that our Chlorine is very effective . 140 English officers have been killed . This is a horrible weapon ...". </P>

When was poison gas first used in world war 1