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In-depth survey report: control technology for crystalline silica exposure during pavement milling using a Roadtec Milling Machine equipped with a local exhaust ventilation system.
Hammond DR; Shulman SA
Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, EPHB 282-25a, 2013 Jul; :1-19
Between September 18th and October 13th, 2012, National Institute for Occupational Safety and Health (NIOSH) researchers and the Silica/Milling-Machines Partnership coordinated by the National Asphalt Pavement Association (NAPA) conducted field testing of a local exhaust ventilation system (LEV) on a Roadtec RX600e cold milling machine. The tests included ten days of air sampling across seven different highway construction sites in Indiana. At each site, full-shift personal breathing zone samples for respirable crystalline silica were collected from the operator and ground man during the course of normal employee work activities of asphalt pavement milling. The data were analyzed two ways, assuming the data were normally distributed and that they were lognormally distributed. For each distribution a 95% upper confidence limit for the arithmetic mean respirable crystalline silica exposure for each occupation was calculated. For the normal distribution analysis, the arithmetic mean respirable crystalline silica exposure for the operator was 0.0049 mg/m3 with an upper 95% confidence limit of 0.0083 mg/m3. The arithmetic mean respirable crystalline silica exposure for the ground man was 0.011 mg/m3 with an upper 95% confidence limit of 0.018 mg/m3. For the lognormal distribution analysis, the arithmetic mean respirable crystalline silica exposure for the operator was 0.0053 mg/m3 with an upper 95% confidence limit of 0.012 mg/m3. The arithmetic mean respirable crystalline silica exposure for the ground man was 0.011 mg/m3 with an upper 95% confidence limit of 0.0246 mg/m3. All 20 full-shift personal breathing zone samples collected from the operator and ground man were below currently published regulatory and recommended occupational exposure limits for respirable crystalline silica. Based on the results of this study, NIOSH researchers recommend that Roadtec should consider refining their design to prevent clogging of the system before making the LEV system a standard feature on all Roadtec half-lane and larger milling machines. A possible solution to prevent clogging would be to further increase the open area at the intake so that the air velocity at the slots is lower without reducing the total volumetric flow-rate of air through the system. A lower intake air velocity should reduce the number of particles larger than the respirable size range of 10 microm from being drawn into the LEV system while keeping the drum housing and primary conveyor under negative pressure. With these modifications, Roadtec should then make the LEV system a standard feature on all of their half-lane and larger milling machines. NIOSH researchers also recommend that other manufacturers of half-lane and larger cold milling machines should consider implementing dust controls that include local exhaust ventilation as a control for silica exposures.
Region-5; Control-technology; Engineering-controls; Construction; Construction-equipment; Milling-industry; Machine-operation; Asphalt-industry; Equipment-design; Equipment-reliability; Performance-capability; Air-sampling; Road-construction; Road-surfacing; Air-sampling-techniques; Breathing-zone; Machine-operators; Construction-workers; Employee-exposure; Exposure-assessment; Silica-dusts; Respirable-dust; Exposure-levels; Exposure-limits; Exhaust-ventilation; Air-flow; Exhaust-systems; Dust-control; Dust-control-equipment; Author Keywords: Silica; Asphalt; Engineering Control
Field Studies; Control Technology
NTIS Accession No.
National Institute for Occupational Safety and Health
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division