Journal of Health and Safety at Work

Introduction: Due to the presence of extreme hazard sources and high intrinsic risk in refineries and process industry sectors, different layers of protection are being used to reduce the risk and avoid the hazardous events. Determining Safety Integrity Levels (SILs) in Safety Instrumented Systems (SISs) helps to ensure the safety of the whole process. Risk Graph is one of the most popular and cost effective techniques to do so. Despite Risk Graph simplicity it’s a qualitative method which is highly subjective and suffers from interpretation problems that can lead to inconsistent or conservative SILs.

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Material and Method: In this paper, Improved Risk Graph (IRG) method was presented and evaluated, and using Fuzzy Logic a novel approach namely Fuzzy Improved Risk Graph (FIRG) was suggested. In the proposed method consequence levels which were defined as qualitative terms were transformed into quantitative intervals. Having those numerical values, risk graph table was converted to a quantitative one. Finally, applying the presented approach and using three experts’ opinions and attributing weight factors, an ultimate numeric value was produced.

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Conclusion: as a result of establishing the presented method, identical levels in conventional risk graph table are replaced with different sublevels that not only increases the accuracy in determining the SIL, but also elucidates the effective factor in improving the safety level and consequently saves time and cost significantly. The proposed technique has been employed to develop the SIL of Tehran Refinery ISOMAX Center. IRG and FIRG results have been compared to clarify the efficacy and importance of the proposed method

Introduction: The purpose of this study was to compare MORT and Tripod Beta methods, using a hierarchical model, in order to choose the best technique to analyze an event in an organization.

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Material and Method: In this study, a critical event was selected and the causes of the event were identified, employing MORT and Tripod Beta capabilities. Following the identification of the event causes, the aforementioned techniques were weighted and compared considering selected criteria and AHP hierarchical method.

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Result: Relative weights of the selected criteria were calculated. The ability to identify the event causes with the weight of 0.315 had the greatest weight. The event analysis cost (0.24), required time to analyze the event (0.146), technical experts (0.125), training for implementation (0.24), and availability of the analytical software (0.07) had obtained the subsequent weights, respectively.

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Conclusion: Analytic hierarchy process is an efficient and practical method to prioritize the choices considering the study objectives and criteria. As scientific method, Analytic hierarchy process helps the experts in decision-making. Considering the selected criteria, findings in this study showed that Tripod Beta technique (with a weight of 0.563) is superior to MORT technique (with a weight of 0.437).