Combustible dusts present an industrial hazard due to their ability to react rapidly and generate dust explosions. Studies have shown that processes utilized to inject and disperse dust particles within combustible dust testing devices result in further comminution of tested materials. Dust explosions are quantified by characteristics Pmax, (dP/dt)max, and Kst-max. This paper investigates the change in physical dust parameters of pulverized Pittsburgh coal, a certification material for ASTM E1226, after dispersion into a Siwek 20-Liter apparatus. Experiments indicate that the change in dust particle size and distribution varies with concentration. Smaller quantities of dust undergo higher levels of comminution. In the case of pulverized Pittsburgh coal all concentrations dispersed had more fines and smaller D10, D50(median), and D90 particle sizes than the pre-dispersion feedstock. Some samples had over a 50% decrease in particle size for D10, D50(median), and D90 which can affect engineering and risk assessment calculations