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In-depth survey report: control technology for dowel drilling in concrete.
Echt A; Mead K; Kovein R
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 347-17a, 2013 May; :1-20
Background: Workplace exposure to respirable crystalline silica can cause silicosis, a progressive lung disease marked by scarring and thickening of the lung tissue. Quartz is the most common form of crystalline silica. Crystalline silica is found in several construction materials, such as brick, block, mortar and concrete. Construction tasks that cut, break, abrade, or drill those materials have been associated with overexposure to dust containing respirable crystalline silica. Highway construction tasks that can result in respirable crystalline silica exposures include breaking pavement with jackhammers, concrete sawing, milling pavement, clean-up using compressed air, and dowel drilling. Dowel drilling machines are used to drill horizontal holes in concrete pavement so that dowels can be inserted to transfer loads across pavement joints. NIOSH scientists are conducting a study to assess the effectiveness of dust control systems sold by dowel drill manufacturers by measuring exposures to workers operating dowel drills with and without dust controls installed. This site visit was part of that study. The dust control assessed at this site consisted of a hood surrounding the drill steel at the drilling surface, flexible duct, an air cleaner, and an air mover. Assessment: NIOSH staff performed industrial hygiene sampling at the Laborer's Local 172 Safety, Education and Training Center in Folsom, New Jersey on August 7 and 8, 2012. The personal sampling measured exposures to respirable dust and crystalline silica among two laborer-instructors who took turns operating a dowel drill to drill holes in a new concrete slab. The NIOSH personnel who visited the site also monitored the weather, collected data (e.g., air flow, design) about the dust collection system and observed the work process in order to understand the conditions that led to the measured exposures. Results: The quartz content in the bulk samples ranged from 17 to 28 percent by weight, with an arithmetic mean quartz content of 22 percent. No respirable dust was detected on any of the personal samples. The minimum detectable concentration was 0.31mg/m3 in a 32 minute sample collected when 27 holes were drilled. Quartz was only detected in one air sample; 0.09 mg/m3 of quartz was found on an 8-minute sample collected during a drill maintenance task. The minimum detectable concentration for quartz in personal air samples collected while drilling was performed was 0.02 mg/m3. The average number of holes drilled during each drilling sample was 23. Over the course of the two day study, air flow measured at the dust collector fell from 2.2 m3/sec (76 cfm) to 1.8 m3/sec (62 cfm). Conclusions and Recommendations: The dust control performed well, under the conditions of this test, controlling the laborers' silica exposures to levels below the NIOSH Recommended Exposure Limit during drilling. The initial duct velocity with a clean filter was sufficient to prevent settling, but gradually fell below the recommended value to prevent dust from settling in the duct. In this site visit, the practice of raising the drill between each hole may have prevented the dust from settling in the duct. A slightly higher flow rate would prevent settling without regard to the position of the drill. The laborers who operated the drill decided to empty the dust collection bucket and clean the filter based on their observations of the dust collection system's performance. The use of gauges to measure static pressure across the filter or at the hood would be a better way to monitor the system's performance.
Region-2; Control-technology; Engineering-controls; Construction; Construction-equipment; Construction-industry; Construction-materials; Construction-workers; Machine-operation; Machine-operators; Equipment-design; Equipment-operators; Respirable-dust; Dusts; Dust-collection; Dust-collectors; Dust-control; Dust-control-equipment; Control-equipment; Control-systems; Concretes; Road-construction; Road-surfacing; Testing-equipment; Silica-dusts; Silicosis; Quartz-dust; Respiratory-system-disorders; Lung-disease; Pulmonary-system-disorders; Lung-disorders; Exposure-assessment; Air-sampling; Air-sampling-equipment; Sampling; Exposure-levels; Exposure-limits; Permissible-limits; Work-practices; Performance-capability; Air-flow; Climatic-conditions; Monitoring-systems; Employee-exposure; Jack-hammers; Drilling; Author Keywords: Silica; concrete; dust; construction; drill; quartz
National Institute for Occupational Safety and Health, Division of Applied Research and Technology, Engineering and Physical Hazards Branch, Mail Stop R-5, 4676 Columbia Parkway, Cincinnati, OH 45226-1998
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Field Studies; Control Technology
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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