This functional area consists of applying engineering, scientific, and analytical disciplines to ensure that design of interactive systems are safer, more secure and easier to use thereby reducing accidents due to human error, increasing system integrity and enabling more efficient process operations. This functional area also includes applying engineering, scientific, and analytical disciplines to ensure that the number, type, mix, knowledge, skills, and abilities (KSAs), aptitudes and physical characteristics of operators, maintainers and support personnel have been defined and documented early in the system design phase.