The SPAR-H method applied in this study could analyze and quantify the potential human errors and extract the required measures for reducing the error probabilities in PTW system. Some suggestions to reduce the likelihood of errors, especially in the field of modifying the performance shaping factors and dependencies among tasks are provided. The PTW process in the studied plant involved four operators including two site men: Site Man 1 (28 years old with 6 months working experience) and Site Man 2 (26 years old with 2 years working experience), one shift supervisor (39 years old with 12 years working experience), and one safety officer (29 years old with 5 years working experience). The PTW procedure consisted of 11 main tasks and four subtasks. Table 1 presents the level of PSFs and calculated PSFc in each task of the PTW process for all the operators involved. Table 4 presents the values of HEPD, HEPA, HEPWO/D, HEPW/D, and total HEP for each task in the PTW process. Accordingly, the mean HEP in the PTW process was 0.112. In addition, the highest probability of human error related to flammable gas testing. The comparison of HEP among different occupational groups involved in the PTW procedure has been presented in Fig. 2. According to this figure, among the individuals involved in the PTW process, site men had the highest probability of human errors. A sample of the SPAR-H worksheet used for the evaluation of PSFs and determination of dependency in the “flammable gas testing” task have been shown in Table 2, Table 3, respectively. The mean probability of human error in the PTW system was estimated to be 0.11. The highest probability of human error in the PTW process was related to flammable gas testing (50.7%). CLICK HERE to see this very interesting study!!