A modern large electrical power plant, powered by nuclear energy, fossil fuels hydro, etc., is a complex human-machine system that controls a thermodynamic process used to produce electrical power. The machine side of the system is a sophisticated arrangement of hardware and software components that are highly reliable, redundant and have a high degree of interconnectedness. The human side of the human-machine system is really a large socio-technological organization with management, engineering, maintenance, operations, and training personnel. Operations personnel interact with the plant through a wide variety of interfaces included in the main control room and various remote monitoring and control stations. Their actions are supported by plant operating procedures and a variety of human-system interfaces (HSI) such as alarm systems, information display systems, controls, diagnostic aids, and communication systems. The safety of such a complex system is supported by extensive analysis of failure modes and mechanisms, engineered features to handle process disturbances, and preplanned human responses to analyzed failures.