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SILICA
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NIOSH: Wet Methods Not Enough to Control Silica Exposures at Countertop Manufacturer
NIOSH recently found overexposures to respirable crystalline silica when agency investigators were asked to evaluate employees’ exposures in a manufacturing plant that makes natural and engineered stone countertops. According to NIOSH’s new health hazard evaluation (HHE) report, the Texas Department of State Health Services requested the agency’s assistance after the department was notified in May 2014 of a worker who had been diagnosed with silicosis—the first reported case in North America caused by occupational exposure to quartz surfacing materials. The worker had been employed as a polisher, laminator, and fabricator at the stone countertop manufacturer for approximately 10 years.
NIOSH’s investigation, which took place in April 2015, included air sampling for respirable crystalline silica, evaluating the plant’s ventilation system, reviewing the company’s safety and health records, and observing work activities, production processes, and the use of personal protective equipment. While the company used wet methods to control dust, NIOSH found that employees using grinders with diamond-cup wheels were exposed to levels of respirable crystalline silica at or above OSHA’s permissible exposure limit (PEL) of 50 μg/m3, NIOSH’s recommended exposure limit (REL) of 50 μg/m3, and the ACGIH threshold limit value (TLV) of 25 μg/m3. Plant employees working in material handling and lamination were also exposed to crystalline silica; while their exposures did not exceed the OSHA PEL, they were above other recommended limits such as ACGIH’s TLV. NIOSH staff found detectable levels of respirable crystalline silica for all other production jobs, but did not find detectable exposure to respirable dust containing crystalline silica or respirable crystalline silica for employees working in the office areas adjacent to the facility’s production shop floor.
The Texas Department of State Health Services was notified in May 2014 of a worker who had been diagnosed with silicosis—the first reported case in North America caused by occupational exposure to quartz surfacing materials.
“Our findings indicate that water suppression alone was not sufficient in reducing crystalline silica concentrations below OELs,” NIOSH researchers reported. “A recent study showed that a combination of water suppression and local exhaust ventilation is more effective than water suppression alone in reducing crystalline silica concentrations. This approach could be applied to this facility to help reduce airborne crystalline silica concentrations.”
To decrease exposures, the NIOSH report recommends the use of engineering controls, including local exhaust ventilation to capture crystalline silica particles at the source in addition to wet methods already in use at the plant. NIOSH also urges the employer to develop a medical surveillance program for employees who are exposed to silica to help prevent long-term adverse health effects. In addition, the employer should retrain workers on the use of N95 filtering facepiece respirators and review the plant’s written respiratory protection program and update it as needed.

In 2015, OSHA and NIOSH issued a joint hazard alert on crystalline silica exposures during the manufacture, finishing, and installation of stone countertops. The alert describes how silica exposure can be mitigated in most countertop operations by monitoring the air to determine worker exposures to silica; controlling dust exposures through engineering controls and safe work practices; and providing respiratory protection to workers when needed. More information is available on AIHA’s website.
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