The effect of particle size on the maximum permissible oxygen concentration to prevent dust explosions

The oxygen concentration in the gas phase at the boundary between an explosion and no explosion in a dust cloud, y_o^b, has been investigated for several particle sizes and for mixtures of coarse and fine dusts of the same material. The maximum permissible oxygen concentration, y_o^m, at which no explosion is obtained has also been determined. Measurements for several type of materials were made in the modified version of the standard small vertical tube apparatus. Nitrogen was used as the inert gas and a train of sparks as the source of ignition. The results obtained indicated that the oxygen concentration is dependent on the particle size, that is, values of y_o^m decrease with a decrease in the size of the particles. Below 100 μm, values of y_o^m become almost constant. Admixture of fine dust as low as 5% to coarse dusts is sufficient to reduce the y_o^m values severely.