A concept that has developed in recent years, especially in connection with toxic substances (insecticides, mercurials, carcinogens), food additives, air and water pollution, and related environmental concerns. It may be defined as a level of risk at which a seriously adverse result is highly unlikely to occur, “but at which one cannot prove whether or not there is 100% safety. It means living with reasonable assurance of safety and acceptable uncertainty.” (Schmutz, J. F., Chemical and Engineering News, Jan. 16, 1978). Examples of acceptable risk that might be cited are diagnostic X rays, fluoridation of water, and ingestion of saccharin in normal amounts. The acceptability of the risks involved in nuclear power generation is controversial. The weight of the evidence has tended to shift toward the negative side since 1975 when an official safety study estimated the risk of a serious accident to be 1 in 20,000 years of reactor operation. An investigation made by the Oak Ridge National Laboratory based on data collected from 1969 to 1979 concluded that the risk of a major accident is 1 in 1000 years of reactor operation.
