either of two isomeric colourless, nonflammable liquids belonging to the family of halogenated hydrocarbons.

One isomer, 1,1,1-trichloroethane, was used as a solvent for cleaning and degreasing metal and electronic machinery. It was also used as a coolant and in the manufacture of other chemicals and products, including insecticides and household cleaners. It was produced by the reaction of 1,1-dichloroethylene and hydrogen chloride.

A small amount of 1,1,1,-trichloroethane is converted to chlorine in the atmosphere, which can cause harmful damage to the ozone layer. As a result, the production of 1,1,1-trichloroethane was banned by the Montreal Protocol in 1996 and has since been slowly phased out of use in countries around the world.

While 1,1,1-trichloroethane is moderately toxic to humans, causing dizziness, loss of coordination, and arrhythmia (irregular heartbeat) only at high levels of exposure, the other isomer, 1,1,2-trichloroethane, is very toxic and may be mutagenic and carcinogenic in humans subject to chronic exposure. The isomer 1,1,2-trichloroethane is made from acetylene, hydrogen chloride, and chlorine, or from ethylene and chlorine. Its principal use is in the manufacture of 1,1-dichloroethylene (vinylidene chloride).