This is a companion volume to Environmental Health Criteria 193: Phosgene. Phosgene is a colourless gas at room temperature and standard pressure. It has a suffocating odour similar to mouldy hay. Although the odour of phosgene can be perceived at 1.6 mg/m3 (0.4 ppm), after adaption recognition will be at levels >6 mg/m3 (1.5 ppm). It is slightly soluble in water and freely soluble in most liquid hydrocarbons, benzene, toluene and glacial acetic acid.