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In-Depth Survey Report: Concrete Surface Preparation Tools Machine 1
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2015/06/01
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Description: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, grind, abrade, or drill those materials have been associated with overexposure to dust containing respirable crystalline silica. Colored, stained, and polished concrete floors are increasingly popular for use in homes, offices, retail establishments, schools, and other commercial and industrial settings. Some businesses specify integrally-colored concrete floors in new stores in place of vinyl composite tile. Polished concrete floors are durable, sanitary, and easy to maintain. NIOSH scientists are conducting a study to develop and evaluate engineering control recommendations for respirable crystalline silica from concrete polishing operations. This survey was part of that study. NIOSH staff visited the Operative Plasterers' and Cement Masons' International Association (OPCMIA) facility in New Brighton, MN from March 25 - 26, 2014. During the site visit, personal breathing zone air samples were collected to measure the respirable dust and respirable crystalline silica exposures of the operator while he used a concrete polisher (Prep-Master 2420, Substrate Technology, Inc., Morris, IL). Additionally, area samples were collected on top of the machine and at four locations around it during the polishing task. The Prep-Master 2420 floor polisher was outfitted with a local exhaust ventilation system consisting of two exhaust ports located on the back of the shroud that encased 12 polishing tools. The exhaust from both ports was connected to a vacuum system rated at approximately 10194 liters per minute (L/min) (360 cubic feet per minute (cfm)) of suction. The vacuum was equipped with a pre-separator. Once through the pre-separator, the air stream was High Efficiency Particulate Air (HEPA) filtered and then recirculated to the room. The aim of this survey was to collect emissions data from the concrete polisher using different grits while operating the dust collection system provided with the machine. Sample times varied based on the length of time needed to polish a rectangular area of 20 square-meters (m2) (216 square-feet (ft2)) with a given grit and ranged between 24 to 49 minutes with an average sample time of 31.8 minutes. Overall, the air samples ranged from 23 to 38% quartz. The mean quartz percentage for all of the air samples was 28.5%. A bulk sample was collected from the dust captured in the bag filter of the vacuum system connected to the concrete polisher
it contained 45% quartz. No cristobalite or tridymite were detected in the bulk sample. Therefore, for the purposes of this report the terms respirable crystalline silica or respirable quartz may be used interchangeably. If exposures were to continue throughout the entire workday and assuming steady, constant, and similar dust generation rates as those measured during this survey, personal breathing zone quartz concentrations using the Prep-Master 2420 concrete polisher fitted with the vacuum dust collection system described above would have ranged from 5 to 63 times the NIOSH Recommended Exposure Limit (REL) for respirable quartz of 50 micrograms per cubic meter (ug/m3) as a time weighted average, depending on the grit selected. The metal bond grits produced about 25% less respirable dust and respirable quartz than the resin bond grits when the personal operator's breathing zone samples were compared. The air sampling results were similar between the two metal bond grits used in this survey. However, when the operator switched from the metal to the resin bond grits (samples collected when using Resin 3), a large amount of respirable dust and respirable quartz was measured in the sample results. Once the floor space was polished with Resin 3, the remaining resin bonds (Resins 4, 5, and 6) did not generate as much respirable dust or respirable quartz as Resin 3, but still generated more than twice the amount of dust measured when using the initial metal bond grits. The Prep-Master 2420 concrete polisher evaluated in this survey was equipped with a local exhaust ventilation system intended to control and remove dust particles generated during the concrete polishing process. However, the dust control system needs modifications so that worker exposure to respirable crystalline silica can be reduced during concrete finishing operations.
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Pages in Document:1-20
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NIOSHTIC Number:nn:20046410
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NTIS Accession Number:PB2015-105625
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Citation: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 368-11a, 2015 Jun;:1-20;
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Federal Fiscal Year:2015
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Peer Reviewed:False
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[PDF-1.36 MB]