Severity parameters are critical for safety management and risk assessment of coal dust explosions. We evaluated explosion severity parameters using a 20-L spherical vessel and numerical simulation by the program FLUENT to reveal the explosion mechanism of coal dusts. The explosion pressure and the rate of explosion pressure increased with coal dust concentration and the ignition delay up to a concentration of 250 g/m(3) coal dust and an ignition delay of 60 ms for a maximum explosion pressure of 0.67 MPa and a rate of explosion pressure rise of 68.89 MPa/s. Comparison of the numerical and experimental explosion pressure profiles showed reasonable quantitative and qualitative agreement. Additionally, the numerical simulation was used to address the technical difficulties of understanding the mechanisms of dust explosion, it suggested that the airflow of the dust explosion played a more important role in the secondary explosion of dusts in a closed chamber than in a half-closed one.