Analysing the impact of deviations in task performance when a user error may have safety-critical consequences

Interactive safety-critical applications have specific requirements in the design cycle that cannot be completely captured by traditional techniques. In this paper we present a proposal aiming to support designers in analysing the space of design solutions and improve both usability and safety of the system considered. This is achieved by focusing the attention of designers on what can happen when abnormal interactions and behaviours occur while users carry out their activities. The result of the analysis can be contained in tables that can be useful to represent design rationale and suggestions for improvements.