The hybrid method combined STPA and SLIM to assess the reliability of the human interaction system to the Emergency shutdown system of LNG ship-to-ship bunkering

By introducing autonomous or software-controlled systems, human operators are increasingly required to perform cognitive-intensive tasks in addition to existing labour-intensive tasks. As a result, it will be more difficult to identify human roles in future complex systems with traditional approaches such as hierarchical task analysis used in the conventional HRA. This paper proposes a novel systematic approach for a human reliability assessment to better understand human activities in complex systems. The proposed framework is a hybrid method combining the System Theoretic Process Analysis (STPA) and the Success Likelihood Index Method (SLIM) to assess the system reliability. The STPA is adopted to analyse the interaction relationship between different system components. The primary purpose of STPA is to find and analyse human activities that affect the risk in human-machine interaction systems. Then the identified human activities are evaluated and quantified by the SLIM as a probability of human error. The system reliability block diagram represents the derived human error probabilities to assess the entire system for a probabilistic risk assessment. Furthermore, the study proposed system alternations by comparing three different system configurations. Results demonstrate the importance of human performance in a complex system where humans, machines, and software interact.