The application of bow-tie method in hydrogen sulfide risk management using Layer of Protection Analysis (LOPA)

Safety systems need to be used in strong and stable ways to achieve the objectives and goals of organizations. The main role of safety systems is highlighted ever than before in maintaining personnel health, environmental protection and improves the reputation of the organizations. Proper functioning of safety system depends on the reliability and the failure probability of the system, which determines the integrated system safety. In this regard, this study aimed to H₂S risk management using bow-tie model with an emphasis on Layer of Protection Analysis (LOPA). An oil processing and gas injection plant is selected as a case of study with considering the high concentration of H2S (130,000 ppm) as well as very high pressure of gas injection (410 bars). This work commences when hazardous regions is categorized according to H₂S gas leakage resources which followed by H₂S risk assessment (bow-tie model). In the following stage, intelligent safety systems were investigated as one of the LOPAs. Thus, the elements of intelligent safety systems are specified. Based upon the software-defined logic, block diagrams were determined. Then, Probability of Failure on Demand (PFD) and Safety Integrity Level (SIL) were attained. PFD of block diagrams was calculated, and corresponding SIL was obtained using Reliability Block Diagram and the relationships between PFD and reliability. As a result, each of elements or block diagrams was considered the weak points. Accordingly, solutions were proposed to reduce the adverse effects and promote SIL to improve safety performance of plant.