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 GMI Engineered Products, LLC (GMI) training facility in Columbus, OH from July 09 - 10, 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 two different concrete polishers (HTC and Husqvarna units). Additionally, area samples were collected on top of the machines and at four locations around the polishing area during the completion of the task. Both polishers were outfitted with a local exhaust ventilation system consisting of two exhaust ports located on the back of the shroud that encased nine polishing tools. The exhaust from both ports was connected to a vacuum system that provided a maximum theoretical airflow of 13,479 liters per minute (L/min) or 476 cubic feet per minute (cfm) of suction. The vacuum was equipped with a pre-separator. Once through the pre-separator, the air stream was HEPA filtered and then recirculated to the room. The aim of this survey was to collect emissions data from the concrete polishers using different grits while operating the dust collection system provided with the machines. Sample times varied based on the length of time needed to polish a rectangular area of 15.8 square-meters (m2) [170 square-feet (ft2)] with a given grit and ranged between 24 and 38 minutes with an average sample time of 31 minutes. Overall, the air samples measured from 10 to 28% quartz. The mean quartz percentage for all of the air samples was 17%. Bulk samples were collected from the dust captured in the bag filters of the vacuum systems connected to the concrete polishers

it contained 19% quartz. No cristobalite or tridymite were detected in the bulk or air samples. 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 below the limit of detection (LOD) to 29 micrograms per cubic meter (microg/m3). All the recorded concentrations are below the NIOSH Recommended Exposure Limit (REL) for respirable quartz of 50 microg/m3 as a time weighted average for each of the grits evaluated during this visit. The polishing process begins with the use of coarse diamond segments bonded in a metallic matrix and then switching to a finer resin bonded grit. The metal bond grit produced, on average, about 50% less respirable dust and respirable quartz than the resin bond grits. When switching from the metal to the resin bond (Resin 50), a larger amount of respirable dust (158 microg/m3) and respirable crystalline silica (29 microg/m3) was measured in the sample results. This is due to the initial finer polishing over a coarse aggregate on the concrete pad generating finer dust than with the previous metal bond. Once the floor space was polished with Resin 50, three of the remaining resin bonds (Resins 200, 400, and 800) did not generate as much respirable dust or respirable crystalline silica as Resin 50, but still produced over twice the dust generated with the initial metal bond grit. The final resin bond (Resin 1500) produced comparable dust levels as Resin 50. Both, the HTC and Husqvarna concrete polishers evaluated in this survey were equipped with an engineering control, a local exhaust ventilation (LEV) system intended to control and remove dust particles generated during the concrete polishing process. The dust control system adequately controlled worker exposure to respirable crystalline silica during this site visit. Additional evaluation is recommended to collect repeated samples using the same equipment. Also, it would be useful to quantify the actual airflow of the vacuum system and establish a correlation between the actual and the listed airflow [13,479 L/min (476 cfm)].