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 375-12a, 2016 Sep; :1-27
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 materials, such as brick, block, mortar and concrete. Construction and manufacturing tasks that cut, break, grind, abrade, or drill those materials have been associated with overexposure to dust containing respirable crystalline silica. Stone countertop products can contain >90% crystalline silica, and working with this material during stone countertop fabrication and installation has been shown to cause excessive exposures to respirable crystalline silica. NIOSH scientists are conducting a study to develop engineering control recommendations for respirable crystalline silica from stone countertop fabrication and installation. This site visit was part of that study. Assessment: NIOSH scientists visited Stone Systems of Minnesota, Mendota Heights, Minnesota on August 25-26, 2015. During the site visit, they performed industrial hygiene sampling which measured the short term task-based exposures to respirable dust and respirable crystalline silica of six workers who used handheld tools in the stone countertop fabrication process. The evaluated work tasks predominantly included polishing (i.e. "Polishers") and grinding (i.e. "Grinders"). An engineering control measure that supplied water to the tools to suppress the dust at its source was used throughout the fabrication process. Local exhaust ventilation was also in place for the Grinders. The NIOSH scientists recorded detailed survey notes about the work process to understand the conditions that led to the measured exposures. Results: Air sampling for respirable crystalline silica showed that the short term respirable crystalline silica exposures ranged from 21.4 to 122.9 microg/m3 for the Polishers, and from 114.8 to 583.2 microg/m3 for the Grinders. The geometric mean short term respirable crystalline silica exposures were 65.7 and 223.3 microg/m3 for Polishers and Grinders, respectively. The Grinders' short term respirable crystalline silica exposures were significantly higher than the Polishers' exposure (p<0.0001). The geometric mean silica contents of the respirable dusts samples were 38.1% and 62.2% for Polishers and Grinders, respectively. The Grinders' respirable dust samples contained significantly more crystalline silica than the Polishers' respirable dust samples (P<0.0001). Conclusions and Recommendations: The results from the task-based samples in this survey revealed that wet grinding and wet polishing engineered quartz stone may still lead to overexposure to respirable crystalline silica. The exposure levels for wet grinding were especially concerning. Using a larger amount of water through a center water feed for the grinders may be the first choice for a future test of control technologies. Additional and more effective engineering control measures will be needed for these tasks to reduce the exposure to levels consistently below the NIOSH Recommended Exposure Limit (REL). In the absence of sufficient dust controls, respirators should continue to be used to reduce exposures, and the employer needs to make sure that the respiratory protection program follows the OSHA standard.
Region-5; Silica; Silica dusts; Stone processing; Quartz; Quartz dust; Construction materials; Engineering controls; Control technology; Dust control; Dust exposure; Respirable dust; Stone products; Respirators; Respiratory protective equipment; Respiratory protection; Task performance; Short term exposure; Dust suppression; Exhaust ventilation; Air sampling; Dust analysis; Dust sampling; Industrial factory workers; Employee exposure; Exposure assessment;
Author Keywords: Cut Stone and Stone Product Manufacturing; Respirable dust; Respirable crystalline silica; Stone countertop; Engineering control; Stone Systems of Minnesota