Mining Publication: Evaluation of the Approach to Respirable Quartz Exposure Control in U.S. Coal Mines

Occupational exposure to high levels of respirable quartz can result in respiratory and other diseases in humans. The Mine Safety and Health Adminstration (MSHA) regulates exposure to respirable quartz in coal mines indirectly through reductions in the respirable coal mine dust exposure limit based on the content of quartz in the airborne respirable dust. This reduction is implemented when the quartz content of airborne respirable dust exceeds 5 percent by weight. The intent of this dust standard reduction is to restrict miners’ exposure to respirable quartz to a time-weighted average concentration of 100 microg/m3. The effectiveness of this indirect approach to control quartz exposure was evaluated by analyzing respirable dust samples collected by MSHA inspectors from 1995 through 2008. The performance of the current regulatory approach was found to be lacking due to the use of a variable property - quartz content in airborne dust - to establish a standard for subsequent exposures. In one situation, 11.7 percent (4370/37,346) of samples that were below the applicable respirable coal mine dust exposure limit exceeded 100 microg/m3 quartz. In a second situation, 4.4 percent (895/20,560) of samples with 5 percent or less quartz content in the airborne respirable dust exceeded 100 microg/m3 quartz. In these two situations, the samples exceeding 100 microg/m3 quartz were not subject to any potential compliance action. Therefore, the current respirable quartz exposure control approach does not reliably maintain miner exposure below 100 microg/m3 quartz. A separate and specific respirable quartz exposure standard may improve control of coal miners’ occupational exposure to respirable quartz.