Numerous studies suggest that 80% of accidents in hydrocarbon processing industries are as a result of human factors (HFs). While a lot is known of human factor influence to process accident, the effects of performance influencing factors (PIFs) on human factors in process accidents is not yet well understood. This study examined HFs and PIFs which influences the propagation of undesired occurrences in hydrocarbon processing industries. An illustrative case study of the Tesoro refinery accident was analysed. To affirm consistency in judgments, Analytic Hierarchy Process AHP – a multi-criteria decision-making method was used in identifying HFs and PIFs of critical events. BPMSG AHP computer program was also used to validate results obtained from the manual calculations. Three critical events namely non-routine operations (Event 1), manual manipulation of several isolation block valves (Event 2) and automated start-up operations of Naphtha Hydro-Treating unit (Event 3) were identified. The ranking of PIFs revealed that Procedures, Level of Supervision, Task Characteristics, and Skill Level were major influencing factors to the event. Analysis of human factors revealed that Job Factors had the most significant influence (41%), while the Individual Factors and Organisational Factors had (31%) and (28%) influence respectively. The consistency index (CI) and consistency ratios (CR) of the PIFs were 0.174 and 0.193 for critical Event 1; 0.170 and 0.120 for critical Event 2; and, 0.037 and 0.033 for critical Event 3 respectively. This showed consistency in judgments of the study on PIFs selected for the critical events identified. The Tesoro refinery accident was due to latent organisational and cultural failures.

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