Quantitative Human Error Assessment Using Engineering Approach in Permit to Work System in a Petrochemical Plant

Permit to work (P.T.W) is a formal written system to control certain types of work which are identified as potentially hazardous. Although P.T.W is a means of safety system and coordinating different work activities to avoid conflicts, it may be susceptible for human error. The purpose of this study was quantitative human error assessment using engineering approach in P.T.W in a petrochemical plant. In this cross-sectional study, P.T.W procedure was analyzed using Hierarchal Task Analysis (HTA). Then, performance shaping factors were identified and were used to estimate the probability including skill based (S.K), rule based (R.B) and knowledge based (K.B) behaviour modes. Finally, human error probability in all P.T.W tasks was estimated using engineering approach. Maximum and minimum probability of human error were for flammable gas testing (0.38) and toxic gas and oxygen testing (0.0449) respectively. Among behavioral modes, maximum and minimum probability were for K.B (0.60) and S.B (0.0714) respectively. The total human error probability for all job tasks of P.T.W, was estimated 0.1465. Engineering approach technique, as a practical method, could be applied by safety and human factor specialists for quantification of human error probability in work processes.