Marine accidents highlight the crucial need for human safety. They result in loss of life, environmental harm, and significant economic costs, emphasizing the importance of being proactive and taking precautionary steps. This study aims to identify the root causes of accidents, to develop effective strategies for preventing them. Due to the lack of accurate quantitative data or reliable probability information, we employ qualitative approaches to assess the reliability of complex systems. We collect expert judgments regarding the failure likelihood of each basic event and aggregate those opinions using the Similarity-based Aggregation Method (SAM) to form a collective assessment. In SAM, we convert expert opinions into failure probability using interval-valued triangular fuzzy numbers. Since each expert possesses different knowledge and various levels of experience, we need to assign weights to their opinions to reflect their relative expertise. We employ the Best-Worst Method (BWM) to calculate the weights of each criterion, and then use the weighting scores to determine the weights of each expert. Ranking of basic events according to their criticality is a crucial step, and in this study, we use the FVI measure to prioritize and rank these events according to their criticality level. To demonstrate the effectiveness and validity of our proposed methodology, we apply our method to two case studies: (1) chemical cargo contamination, and (2) the loss of ship steering ability. These case studies serve as examples to illustrate the practicality and utility of our approach in evaluating criticality and assessing risk in complex systems.