A Study on Vent Mast Hazardous Zone Determination Applying EI 15 under the Revised IGF Code

The revised IGF code allows the application of the fuel's 50% LFL contour to define reduced Zone 1 extent around vent mast but provides no guidance on dispersion modeling or release scenario definition. Therefore, engineers often refer to IEC 60079-10-1, which suggests a leak hole size equal to 10% of the PSV orifice area. For large LNG fueled vessel's PSV, this assumption produces unrealistically high release rate and excessively conservative hazardous zone extent. This study proposes a practical alternative approach applying the El 15 Level framework (Level I ~ III), which determines leak hole size based on Individual Risk (IR) and ignition probability. By mapping El 15 equipment type to PSV, more realistic and risk consistent leak hole size is taken while maintaining compliance with IGF code. Two-phase release simulation using DNV Phast and in:Flux CFD dispersion modeling tool were conducted to compare hazardous zone extent from IEC approach and EI 15 based leak hole size. Results show that El 15 leak hole size substantially reduce fuel's 50% LFL contour, below 3 m, while preserving alignment with accepted risk principles. The methodology clarifies scenario selection under the revised IGF code and supports more practical hazardous zone extent design for LNG fueled vessel.