The Bureau of Mines conducted experimental work on comminuting coal. The size distributions of coarse fragments and fine particles were obtained under different modes of energy application--drop, impact crushing, wedge impact, compression, and shear tests. Four levels of energy application were used in the impact crushing and wedge impact tests. Airborne dust and respirable airborne dust distributions were obtained for the impact crushing and wedge impact tests. Analyses of nonairborne dust and coarse fragment-fine particle distributions were carried out on impact, wedge, compression, and shear tests. The experimental size data on nonairborne dust were fitted to normal, log-normal, power law, weibull, log-weibull, and exponential distribution functions. Both the nonairborne dust and the coarse fragment-fine particle size distributions are best described by weibull distributions. For the impact crushing tests, mean product size was found to be inversely related to specific crushing energy. The particle counts in a given size range of airborne and nonairborne dust were found to increase with increased input energy and specific crushing energy. However, in another sense, the particle distributions were independent of energy level; that is, the percentages in a given size range were approximately constant regardless of energy level. Respirable airborne dust was related to respirable-size nonairborne dust by a power law.