Small scale laboratory pulverizing experiments were performed on humidified coal material sieved to size 6.35 mm (0.250 in) and below to eliminate effects due to inherent planes of weakness (cleats or joints). Experimental factors studied include the coal seam proximate analysis constituents, the breakage-in-duced electrostatic field of airborne dust, and the specific airborne dust generated. Results of these pulverizing experiments show that only coals below 1-2 air dry loss (ADL) moisture content are in a higly charged state after pulverization and that the amount of charging decreases rapidly with increasing ADL up to 1-2. This appears to have a direct effect on the specific deust generation characteristics of coals. However, each coal may have its own characteristic dust charge and generation signature. Underground dust samples obtained in coal seams with inherent moisture contents ranging from 0.5 to 4.5 suggest that significant particle agglomeration exists for the 0.5 inherent moisture coal but not the coals with moisture > 1.3 inherent moisture, in agreement with the lavoratory testes.
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