Illustration of a soldier with asphyxia, two days after being gassed with phosgene. The patient died two hours after. Phosgene is a toxic, colourless, chlorine containing gas that disrupts gas exchange in the lungs, causing death from asphyxia. The gas was first used in battle by German forces at Ypres, Belgium in December 1915. used Published in An Atlas of Gas Poisoning, 1918.