In the present research work, the effects of particle size (D-50) and size dispersity (sigma(D)) on the explosion severity of coal dust were investigated using a 20 L spherical explosion vessel. Coal dust samples with similar median diameter (D-50) and different size dispersity (sigma(D)) and similar size dispersity (sigma(D)) and different size diameter (D-50) were specially prepared by mixing original coal samples having a narrow size distribution. The explosion severity of each sample was evaluated by measuring the maximum pressure (P-max) and the maximum rate of pressure rise ((dP/dt)(max)). Interestingly, results show that almost all of the selected coal dusts present the same optimum explosion concentration of 250 g/m(3). The parameters of P-max and (dP/dt)(max) show an increasing trend in explosion severity as size dispersity (sigma(D)) and particle size (D-50) decrease, which indicate a more notable effect due to the contribution of finer coal particles on the dust cloud deflagration dynamics. The higher the volatile matter content, the more severe is the explosion. The presence of the finer particles would greatly increase the total effective specific surface area and speed up the devolatilization rate, which would cause acceleration of the dust explosion process. Furthermore, the effects of dust concentration on the explosion process were analyzed by comparing the defined time span (tau(1)) from ignition point to reach (dP/dt)(max) point and time span (tau(2)) from (dP/dt)(max) point to reach P-max point. For the coal dust with lower D-50 and lower sigma(D), tau(1) and tau(2) are always short. Under lower coal dust concentration condition (<250 g/m(3)), tau(1) and tau(2) present a stronger dependence on sigma(D) and dust concentration. However, the effect of aD and dust concentration on tau(1) and tau(2) becomes weak for the higher coal dust clouds (>250 g/m(3)). Results indicated that the evaluation of coal dust explosion hazard should be considered in terms of not only dust concentration, but also particle size (D-50) and size dispersity (sigma(D)). 2016 Elsevier B.V. All rights reserved.