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In-depth survey report: evaluation of a Volvo milling machine equipped with a wet drum designed to reduce respirable crystalline silica exposure during pavement milling.

Hammond DR; Kovein R; 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 282-24a, 2013 May; :1-16
From August 17-18, 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 Volvo MT-2000 cold milling machine equipped with a wet drum designed to reduce respirable crystalline silica concentrations. The wet drum design uses gravity to release water from inside the drum through nozzles to the cutting surface to suppress dust. The effectiveness of the dust controls examined in this study was evaluated by measuring the reduction in the respirable dust and respirable quartz concentrations in area samples collected during a typical milling job. The test consisted of replicate short-term milling trials (nominally about 10 minutes each in duration). During a trial, the milling machine removed approximately 2-inches of depth of the asphalt surface while operating either its existing production water-spray system (the "baseline configuration"), or its wet drum configuration. Respirable-dust concentrations were measured at ten selected locations around the milling machine using continuous real-time data-logging dust monitors. The results from six key monitoring locations (from among the ten) together are considered to best represent dust-emission rates, because they surround the low-to-the-ground dust-generating areas of the machine where the modified emission controls are located. Trial-mean concentrations from these "lower-six" locations were averaged together to obtain a single lower-six-location average for that trial. Average dust-emission reductions, along with their statistical confidence intervals, were computed for the wet drum configuration versus the baseline. In addition, average dust-emission reductions were also computed for the operator bridge and conveyor top. Full-shift personal breathing zone sampling for respirable dust and respirable crystalline silica was also conducted for the operator and groundman each day. The personal breathing zone samples collected during this study do not provide a direct measure of the control efficiency since the samples include periods of operation of both control configurations. A total of 19 short-term trials were conducted to compare reductions in respirable dust concentrations between the wet drum and baseline water configurations on a Volvo MT-2000 cold milling machine. The results showed a geometric mean reduction in respirable dust concentrations of 37% at the lower-six source locations and 27% at the operator locations. However, these results were not statistically significant at the 95% confidence level. The personal breathing zone sampling results for respirable crystalline silica for the operator were 0.085 mg/m3 on day 1 and 0.028 mg/m3 on day 2. The personal breathing zone sampling results for respirable crystalline silica for the ground man were 0.040 mg/m3 on day 1 and 0.043 mg/m3 on day 2. The results of this study showed that while the wet drum provided an increased level of control over the baseline configuration, there was no statistically significant difference between the two designs. In addition, the magnitude of the exposure reduction does not appear to be sufficient to protect workers from excessive crystalline silica exposures. Based on the results of this study and previous studies, NIOSH researchers recommend that manufacturers of half-lane and larger cold milling machines use local exhaust ventilation as a control for silica exposures.
Region-5; Control-technology; Engineering-controls; Construction; Construction-equipment; Construction-workers; Milling-industry; Machine-operation; Machine-operators; Equipment-design; Equipment-reliability; Performance-capability; Sampling; Road-construction; Road-surfacing; Sampling-methods; Employee-exposure; Exposure-assessment; Silica-dusts; Respirable-dust; Exposure-levels; Dust-control; Dust-control-equipment; Gravitational-forces; Cutting-tools; Quartz-dust; Surface-properties; Dust-samplers; Monitors; Breathing-zone; Emission-sources; Concretes; Testing-equipment; Measurement-equipment; Statistical-analysis; Sampling-equipment; Exhaust-ventilation; Author Keywords: Silica; Asphalt; Engineering Control
7631-86-9; 14808-60-7
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Field Studies; Control Technology
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EPHB-282-24a; M102013
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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