In this study, we conducted a comprehensive risk assessment of gas compressors used in LNG carriers by applying two different methods: Failure Mode and Effect Analysis (FMEA) and System Theoretic Process Analysis (STPA) on model-basis. Gas compressors are critical for the operation and cargo handling of LNG carriers, and their failure could lead to significant operational disruptions. Traditional risk assessments sometimes fail to address the complexity of such systems comprising many components and subsystems and lead to unanticipated failures. To mitigate this, we modeled the hierarchical structure and functional relations between components and performed FMEA We identified 412 failure modes and classified 59 as high-risk. Additionally, we conducted STPA to analyze risks emerging from control interactions within the gas compressor control system. This method allowed us to identify 18 Unsafe Control Actions (UCAs) and 12 loss scenarios leading to these UCAs. By integrating both FMEA and STPA, we derived 13 new risk mitigation measures, which were fed back into the design and operational practices of NYK Line. Our approach demonstrates the effectiveness of model-based risk assessments in providing comprehensive and objective risk mitigation measures, particularly valuable for the safe utilization of new fuels like ammonia and hydrogen. Future work should focus on quantifying risks and verifying effectiveness of risk mitigation measures by applying physical simulations based on the models used in this study.