Standard Respirable Dusts

"There is a considerable need for standardized respirable dusts with consistent, reproducible characteristics which simulate those of actual mine dust. The availability of such materials should be a significant factor in promoting coordinated research into dust characterization and mine monitoring, dust control, and the biomedical aspects of dust toxicology. The use of an opposed-jet, fluid-energy grinding system in closed circuit with a cross-flow, centrifugal air classifier for preparing bulk quantities of respirable-size dust has been investigated, and appropriate, standardized procedures have been established. By stage-crushing, screening, and fine-grinding with a Donaldson Acucut classifier/mini-grinder system, it is possible to produce bulk quantities of respirable dust at relatively high rates. Using minor modifications to the system, broader or narrower size distributions can be prepared within the respirable range. The system has been shown to reach steady-state with respect to product size distribution very rapidly. However, preferential grinding/classification effects appear to lead to a slow build-up of mineral matter in the circulating load with a corresponding slow change in product composition with time. In those applications where the dust composition is required to match that of the feed coal, it may be necessary to allow considerable time for a true steady-state to be established.Standard respirable dust samples have been prepared from coals representing the western (high volitile A bituminous), central (medium volatile bituminous) and eastern (anthracite) mining areas of Pennsylvania. Quartz and kaolin clay samples, representing important mineral constituents of coal dust have also been prepared. Extensive characterization studies have been performed on the samples to evaluate chemical and mineralogical composition and the distributions of particle size and specific gravity. Detailed information on the original coals is available from the Penn State Coal Data Base. The standard coal dust samples appear to simulate actual mine dust very well with respect to particle size and shape, but generally have somewhat lower ash content. Samples of these standard dusts have been made available to research groups concerned with respirable dust in mines."