With the increasing demand for petroleum products in the Asia–Pacific region, the operation of tanker vessels carrying chemicals has increased, leading to growing concerns over leakage incidents. The transportation of liquefied petroleum gas (LPG) poses a significant risk owing to its non-water-soluble nature and low lower explosive limit (LEL), making it highly susceptible to explosions. In the event of an LPG gas leakage at sea, there is a high likelihood of secondary incidents, as gases can spread from the initial accident on the vessel to nearby coastal areas. In this study, we aim to predict the dispersion range of leaked gas from a chemical tanker operating in the coastal waters near Korea Maritime and Ocean University using computational fluid dynamics (CFD) simulations, based on a hypothetical LPG gas leakage scenario. The results showed that leaked gas from tankers operating in the northern, eastern, and southeastern waters reached the coastal area in 8, 15, and 12 s, respectively, spreading over 1/4th, 1/6th , and 1/5th of the total area. Furthermore, even after the gas completely leaked from the vessel, the gas concentration within the coastal area remained within the flammable range for 15, 33, and 36 s, respectively. The analysis of the factors affecting gas dispersion revealed that the size of the leakage outlet had a greater impact than the wind speed. By applying the analytical methods used in this case study, the dispersion range of hazardous gases leaked from vessels navigating coastal routes is expected to be accurately predicted, providing foundational data to improve existing response guidelines.