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In-Depth Survey Report: Concrete Surface Preparation Tools Machine 4
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2016/01/01
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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, Minnesota on July 16, 2014. During the site visit, personal breathing zone (PBZ) 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, Illinois). Additionally, area samples were collected on top of the machine and at four locations around the polishing area during the completion of the 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 twelve 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 passed through a High Efficiency Particulate Air (HEPA) filter 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 11 to 43 minutes with an average sample time of 31 minutes. Overall, the air samples measured from 18 to 36% quartz. The mean quartz percentage for all of the air samples was 30%. A bulk sample was collected from the dust captured in the bag filter of the vacuum system connected to the concrete polisher
it contained 48% 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 as measured throughout the entire workday and assuming constant dust generation rates, PBZ quartz concentrations with the local exhaust ventilation operating would range in concentrations from 3 to 103 times the NIOSH Recommended Exposure Limit (REL) for respirable quartz of 50 micrograms per cubic meter (microg/m3) as a time weighted average, depending on the grit selected. The metal bond grit produced about 90% less respirable dust and respirable quartz than the resin bond grits when the personal operator's breathing zone samples were compared. When switching from the metal to the resin bond grits (Resin 3), a large amount of respirable dust and respirable quartz was measured in the operator 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 over ten times the amount of dust measured when using the initial metal bond grit. The Prep-Master 2420 concrete polisher evaluated in this survey was equipped with a local exhaust ventilation (LEV) 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:20047539
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NTIS Accession Number:PB2016-102602
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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 368-13a, 2016 Jan;:1-20;
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Federal Fiscal Year:2016
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Peer Reviewed:False
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[PDF-1.26 MB]