Ergonomics of protection and interlocks for high integrity systems

Automatic protection and key-operated interlocks are a distinguishing feature of high integrity systems. They are intended to pre-empt human error, or to mitigate its results. Alternatively, they provide automated responses where human reactions are impossible or cannot be guaranteed reliable. Their specification stems from safety analysis and generally they are designed to have very high reliability. However, they are often designed with little consideration for the human factors involved in their operation. This paper considers the author´s practical knowledge of failures of such systems that have actually arise. The factors underlying these are translated into requirements for the design of interfaces, terminology, supporting procedures and training. In particular, the paper focuses upon the factors that must be considered to ensure the end-users´ understanding of systems that are characteristically complex and often also opaque