A conceptual model for the analysis of mishaps in human-operated safety-critical systems

In this paper we provide a conceptual model useful for describing the cyclic interactions of a computer system with its environment and with the humans operating it. Furthermore, it describes how undesirable events introduced at operation time and/or at design time can interact, possibly leading to catastrophic consequences. The model provides a basis for the proper design and analysis of safety-critical systems with human and computer-based components. The model is derived from the requirements engineering reference model of Zave and Jackson by the addition of behavioural dynamics, the inclusion of an operator and feedback. The model looks far beyond individual failures and considers problems not as the chaining of events but as the chaining of deviations from design, from operation and from their interaction. Our goal is a model through which analyses that transcend the traditional reductionist approach in event-chain models can be conducted.