Vinyl Chloride, gas with the chemical composition CHClCH2, which when polymerized produces polyvinyl chloride, or vinyl plastic. The gas, formed by reacting ethylene or acetylene with hydrochloric acid, was once also used as a propellant in aerosols but was banned from that application in 1974 when found to be a carcinogen. The concentrations of vinyl chloride in the workplace are now carefully regulated.