Risk Assessment of an Off-Site Hydrogen Refueling Station: A Hybrid IEC 61511-CCPS LOPA Framework

Off-site hydrogen refueling stations (HRS) handle large volumes of high-pressure hydrogen, requiring precise and systematic risk-reduction strategies. In this study, a Hazard and Operability (HAZOP) analysis was performed for an off-site HRS, and Layer of Protection Analysis (LOPA) was conducted for four risk-level-4 events using two different approaches. The Functional Safety only LOPA, based on IEC 61511, and the All Safeguards LOPA, developed according to the Center for Chemical Process Safety (CCPS) guideline, were both applied. The Functional Safety only approach, which considers only automated protection layers, required Safety Integrity Level (SIL) ratings of 1 and 2, whereas the All Safeguards approach, accounting for mechanical and procedural protection layers, achieved the Target Mitigated Event Likelihood (TMEL) in all scenarios without additional SIL requirements. Consequently, it was confirmed that the definition of protection layer scope significantly influences the required SIL, design cost, and system complexity. This study proposes a hybrid approach in which all safeguards are considered during the early design stage, while in the final design stage, protection measures are evaluated from a functional safety perspective in accordance with IEC 61511 to ensure both design efficiency and safety integrity.