Respirable quartz hazard associated with coal mine roof bolter dust

This study examined the potential for coal mine roof bolter dust to be a source of a worker’s exposure to respirable quartz. For the models of roof bolter studied, the dust from bolt hole drilling is collected by a dry vacuum exhaust system. The collected dust-laden air passes through a cyclone size-separator (pre-cleaner) and into a collector box containing two additional cyclones and a filter cartridge. The filtered air is then discharged through a muffler into the ambient mine air. The pre-cleaner is designed to remove oversize dust, with the pre-cleaner undersize dust passing to a collector box. The pre-cleaner periodically dumps collected dust onto the mine floor. To assess the hazard presented by the roof bolter dust, bulk samples of the pre-cleaner dust and collector box dust were obtained from roof bolters operating in Mine Safety and Health Administration Coal Districts 4, 5, 6, and 7. Forty-six samples of each dust type were collected from twenty-six mines. Dust size distributions were determined for each sample. The quartz content was also determined for forty samples. The fraction of pre-cleaner dust smaller than 10 micrometers ranged from 5.3% to 35.4%. Quartz content, by weight, of the pre-cleaner dust ranged from 9.8% to 53%. The collector box dust was significantly smaller in size with the fraction of dust below 10 micrometers ranging from 13% to 86.7%, its quartz content ranged from 1.0% to 79%. Airborne dust samples along with detailed observations of the bolter operation were collected at two of these mines to further evaluate potential for worker exposure. This study quantifies the high content of respirable quartz in the roof bolter pre-cleaner cyclone dump dust and the collector box dust.