Explosion hazard analysis of LNG tank trucks passing through cross sea bridges after unloading

A small amount of liquefied natural gas (LNG) often remains inside tank trucks after unloading. This paper investigates the safety of LNG tank trucks traversing cross-sea bridges post-unloading. Using the process hazard analysis software tool PHAST, the study calculates methane leakage and dispersion from holes in pipelines connected to LNG tanks, as well as the explosion consequences of methane-air mixtures. An explosion overpressure value of 0.10 MPa is used as the hazard evaluation criterion. The results indicate that even with only 0.10% to 0.50% of the rated filling capacity of the LNG tanks remaining after unloading, if the leakage breach diameters exceed 25 mm, the resulting maximum explosion overpressure may surpass 0.10 MPa. This level of overpressure could cause permanent damage to the reinforced concrete structures of cross-sea bridges. Therefore, to ensure the safety of cross-sea bridges, it is not advisable to allow unloaded LNG tank trucks to pass through these structures.