Safety barrier function analysis in a process industry: A nuclear power application

Accidents in complex industrial systems often originate from interacting technical, organizational and human failures. Barrier functions protect the systems from the negative consequences of failures and errors. The purpose of the present study was to present a general model for and analyse the reliability of the existing barrier functions in the refuelling process in a nuclear power plant. A first step in the analysis was to identify the barrier functions in the refuelling process by constructing an Event and Barrier Function Model. Seventeen barrier functions were identified and classified as technical, human or human/organizational. Secondly, the reliability of the barrier functions were assessed using ratings from two personnel groups working in the process, sixteen plant operators and eleven external operators. Five performance shaping factors (PSFs) as well as six task-specific characteristics (TSCs) were also assessed. The plant operators rated the overall barrier function strength as significantly lower than the external operators. For judgments of contribution to a broken barrier function from PSFs and TSCs there were no significant difference between the two groups. Across groups, two PSFs, fatigue and night shift were rated as contributing more to the possibility of a broken barrier function. This analysis can provide a benchmark for comparison of safety in the refuelling task before and after a technical and organizational intervention.