The growth of large, complex technology systems in recent decades, such as nuclear power plants, commercial aviation, the petrochemical industry, chemical process plants, and marine and rail transport, has spawned rare but often catastrophic events such as organizational or system accidents. The Three Mile Island nuclear accident, the Exxon Valdez oil spill, the Bhopal India gas leak, the Challenger disaster, and numerous airline accidents, among others, caused growing public concern over the terrible costs, loss of life, the risk to the public, and threat to the environment. In most instances, human error was cited as the cause of these incidents.