Re-entrainment of Fine Particulates in Mine Airways

"Re-entrainment refers to dislodgement of particles deposited by both atmospheric and nonatmospheric processes and their subsequent insertion into a flowing field. Formation of sand dunes, snow drifts, soil erosion and fugitive dust emissions are a few examples of the natural occurrence of re-entrainment. Re-entrainment studies have been done for the estimation of potential hazards from nuclear fallouts. The phenomenon of re-entrainment has been utilized for the cleaning of wafers and filters. Re-entrainment is associated with both surface and underground mining activities. However, studies on dust re-entrainment in mine atmospheres are limited. Understanding the re-entrainment phenomenon is important because dust particles lying seemingly harmless on the ground and adhering to numerous surfaces can get re-entrained and become a health and safety hazard.There are significant differences in the kind of re-entrainment encountered in underground mines and those in other fields of interest. These major differences are air velocity, direction of air flow, particle size, amount of particles, and time of exposure. While numerous studies have been done in other fields to identify the role of interacting variables and their contribution to the mechanisms of re-entrainment, no similar reported work is available for dust in mine atmospheres.In this paper, recent research efforts on re-entrainment are reviewed. The most suitable form of representing re-entrainment in underground coal mine atmosphere is presented. Various approaches to studying re-entrainment phenomenon in mines are also outlined.In the mineral industries, formation of dust particles of widely varying sizes is a natural outcome of the fragmentation required in mining the solid resources. Fine particles in mine atmospheres, particularly in the respirable size range, are a threat to the health and safety of the miners when present in high concentrations. In 1980 the National Academy of Sciences (NAS) Committee on the Measurement and Control of Respirable Dust in Mines recommended that the spatial and temporal characteristics (of fragments produced in coal mining) need to be understood so that the exposure of workers to the dust can be controlled. Recently several studies have been performed to understand the fundamental behavior of the airborne respirable dust in mine airways (Bhaskar, 1987; Qin, 1988; Polat, 1989; Bode, 1990)."