Failures without errors: quantification of context in HRA

PSA-cum-human reliability analysis (HRA) has traditionally used individual human actions, hence individual ‘human errors’, as a meaningful unit of analysis. This is inconsistent with the current understanding of accidents, which points out that the notion of ‘human error’ is ill defined and that adverse events more often are the due to the working conditions than to people. Several HRA approaches, such as ATHEANA and CREAM have recognised this conflict and proposed ways to deal with it. This paper describes an improvement of the basic screening method in CREAM, whereby a rating of the performance conditions can be used to calculate a Mean Failure Rate directly without invoking the notion of human error.