Phosgene is the chemical compound with the formula COCl2. A colorless gas, in low concentrations its odor resembles freshly cut hay or grass. Phosgene is a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. It gained infamy as a chemical weapon during World War I where it was responsible for about 85% of the 100,000 deaths caused by chemical weapons. In addition to its industrial production, small amounts occur from the breakdown and the combustion of organochlorine compounds, such as those used in refrigeration systems. The chemical was named by combining the Greek words "phos" (meaning light) and "genesis" (birth); it does not mean it contains any phosphorus (cf. phosphine).