tokens: We investigated an epidemic of liver disease in nine industrial workers who had had repeated accidental exposure to a mixture of 1 , 1 - dichloro - 2 , 2 , 2 - trifluoroethane ( HCFC 123 ) and 1 - chloro - 1 , 2 , 2 , 2 - tetrafluoroethane ( HCFC 124 ) .