Rational drilling control parameters to reduce respirable dust during roof bolting operations

Abstract

Roof bolting has been the primary means to improve mine safety in the aspect of preventing different types of roof falls in underground mines. However, based on the published researches, underground roof bolting operators exhibit a continued risk for overexposure to high levels of respirable coal and crystalline silica dust from the roof drilling operation. Inhaling these dust can cause coal workers’ pneumoconiosis (CWP), also known as black lung. Another job-related lung disease silicosis, a disabling and even fatal and irreversible illness, could be developed through overexposure to quartz-laden dust. A recent NIOSH research shows that the quartz content in the total roof bolting dust can be as much as 50% and 20% of them are 5 µm or smaller in size. Dust in this size range is even fatal because the chance for them to reach the gas-exchange region of the lung and being deposited increased dramatically. Therefore, rock drilling in roof bolting operation could be the major quartz source for causing silicosis to this group of underground miners. Even with engineering controls and federal regulations in place, new cases of black lung and silicosis continued to be reported and seen in young miners. This research is focused on the development of controlled drilling technique for roof bolt drilling dust reduction purpose. It can be an important approach to reduce the harmful dust from its generation source. Different from conventional passive engineering controls, this approach is a proactive one that can cut down the generation of harmful dust from its source. A bolt-hole drilling mechanical model, as an analytical tool to identify the most influential drilling parameters to the energy consumption and dust generation was developed. Laboratory drilling tests were conducted to validate the mechanical model and the dust samples were collected and analyzed to investigate the relationship between the cumulated respirable dust productions with different drilling bite depths. The effect of bit wear, bit size and rock material on dust generation and energy consumption was evaluated as well. The generated respirable dust was mainly collected by the pre-cleaner and dust-bag. The effect of drilling bite depth on energy and dust generation was analyzed for all the tests. An exponentially decreasing trend was observed between drilling specific energy and bite depth. While the dust generation characteristics showed a considerable reduction in both inhalable and respirable dust generation rate when increasing bite depth from 0.15 to 0.60 cm/rev (0.059 to