Chemical accidents generated during maintenance, repair, and normal operation, such as dispersion, fire, and explosions, can cause massive losses within and outside workplaces. Since a 2012 hydro fluorine leak in Gumi, South Korea, many studies have investigated mitigation systems for reducing accident impact. However, due to potential costs, and lack time and expertise, most companies have hesitated to install mitigation systems without accurate impact evaluations. Therefore, it is essential to analyze mitigation system efficacy under various possible accident scenarios. We considered a mitigation system incorporating a reserve vessel installed next to a storage vessel. When a leakage accident occurs, the chemical in the main vessel is transferred to the reserve vessel by a pump. Simulation results based on Torricellis’ theorem indicate that this mitigation system could significantly reduce leakage, and reduce leakage consequences in terms of maximum diffusion distance and hazardous gas concentrations based on consequence analysis.