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Effects of spray surfactant and particle charge on respirable dust control.

Raynor PC
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-009768, 2013 Dec; :1-21
Inhalation exposures to respirable coal dust are a serious health concern for underground coal miners. One method used to limit these exposures is to spray water that contains surfactants to capture the airborne particles near the mining face. The goal of this research was to determine if surfactants that carry an electrical charge can enhance respirable particle capture through electrostatic attraction. In a laboratory setting, tests were conducted to measure the effects of particle diameter, surfactant type and concentration, and particle charge on the capture of respirable particles by surfactant-containing water spray droplets. Polystyrene latex particles with diameters of 0.6, 1.0, or 2.1 um or coal dust particles with a wide range of diameters were generated in a wind tunnel. Particles were given either an unneutralized, neutralized, net positive, or net negative charge, and then were allowed to be captured as they passed through sprays containing anionic, cationic, or nonionic surfactant, or they moved through the same spray section with the spray turned off. After passing through the spray region, the particles were sampled, charge-separated, and counted at various voltage levels. Comparisons of concentrations with the sprays on and off permitted the calculation of collection efficiency. Overall efficiencies were measured integrated across all charge levels, as well as efficiencies for particles at specific charge levels. The overall collection efficiency rose significantly with increasing particle diameter. Collection efficiencies of 22%, 59%, and 87%, on average, were observed for polystyrene latex particles 0.6, 1.0, and 2.1 um in diameter, respectively. The combination of surfactant classification and concentration significantly affected both overall spray collection efficiency and collection efficiency for particles with specific charge levels. Anionic (negatively-charged) and cationic (positively-charged) surfactant sprays had the best performance with charged particles having the opposite sign of charge and the worst performance for charged particles holding the same sign of charge. Nonionic surfactant-containing spray removed particles carrying relatively few charges more efficiently than the anionic or cationic surfactant sprays. Particle charge level impacted the spray collection efficiency as highly-charged particles were removed more efficiently than weakly-charged particles. Comparisons of measurements made with the polystyrene latex particles and the coal dust particles showed similar efficiency, indicating that the polystyrene particles are a suitable surrogate for the coal dust particles.
Surfactants; Particulates; Respiration; Electrical-charge; Sprays; Respirable-dust; Exposure-levels; Fibrosis; Risk-factors; Coal-dust; Dusts; Dust-exposure; Coal-mining; Airborne-dusts
Peter C. Raynor, Ph.D., Associate Professor, University of Minnesota, Division of Environmental Health Sciences, Mayo MC 807, 420 Delaware Street S.E., Minneapolis, MN 55455
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National Institute for Occupational Safety and Health
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University of Minnesota
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division