Long-term exposure to excessive levels of respirable coal mine dust can lead to coal workers’ pneumoconiosis (CWP), a debilitating lung disease commonly known as "black lung." The last 35 years have seen major gains in the national effort to reduce CWP. The percentage of dust samples exceeding the 2 mg/m3 federal regulatory limit for continuous miner workers has dropped from 49% to 9%. For longwall workers, the percentage has dropped from 44% to 12%. Likewise, the prevalence of CWP category 1/0+ or higher has dropped from 28% to 8%.

These improvements are due in great part to the development of new dust control technology by NIOSH. Of course, new technology was not the only cause for these improvements. Strong enforcement by the Mine Safety and Health Administration (MSHA) and changing attitudes within the coal industry were vital. Nevertheless, NIOSH made a critical and essential contribution by providing the engineering control tools to make these improvements possible.

Our research has resulted in dozens of new and practical ways to control dust that are now used every day in the coal industry throughout the United States. For example, research for longwalls has identified optimum spray types and locations in cutting drums, developed directional spray systems for the longwall shearer, identified optimum operating pressures for different water spray types, demonstrated methods to control dust from crusher/stageloader units, and improved operating practices such as worker positioning and cutting practices.

MSHA has played a valuable role in promoting NIOSH-developed technology. For instance, in 1999, MSHA placed a Longwall Dust Control Toolbox on its website to guide longwall operators in their efforts to control respirable dust. Most of the control technologies shown in this toolbox were developed by NIOSH, with 28 of the 32 cited publications reporting on our research findings.

At the same time that new techniques were being developed to reduce dust, countertrends within the industry were underway. Production levels on both continuous miner and longwall sections were undergoing huge increases. Compared to 1971 levels, the 2003 shift production at continuous sections more than doubled. Longwall production increased nearly tenfold. Higher production means more dust. Nevertheless, the new dust controls being introduced were so numerous and so effective that compliance with federal dust standards continued to improve.

Although significant reductions in average worker overexposures and CWP have been achieved, shift production levels continue to increase. Thus, the task of protecting miners from respirable coal dust is far from finished. For example, today the highest production continuous miner sections are producing over 2,000 tons per shift, while the highest production longwalls routinely produce over 15,000 tons per shift. This represents about 2.5 times the average for the industry. Further improvements in control technologies are still needed, particularly for a number of high-risk occupations.

In recent years, NIOSH has developed dust control technologies that build on or supplement the controls already being used. For example, continuous miner research showed that blocking sprays, if properly used, can reduce dust levels at the operator locations. Blocking sprays create a water barrier near the cutting face, which prevents dust from rolling back to the operator locations at the back of the machine and allows the dust to be captured by the scrubber inlets. A major continuous miner manufacturer now offers blocking sprays on its machines, and new continuous mining machines are underground with these sprays installed. NIOSH researchers also found that thinner filters were being used in flooded-bed scrubbers on continuous miners. Research showed that these thinner filters allowed 30% more dust back into the mine air. NIOSH recommended the use of thicker filters in a NIOSH Hazard ID flyer. MSHA requested 1,000 copies of this Hazard ID to distribute to mine inspectors as part of its initiative to lower silica dust exposure. MSHA has also required mine operators to use these thicker filters when dust problems exist and currently requires the industry to specifically identify these filters in dust control and ventilation plans.

In 2003, all of the dust control technologies that we developed over the years and that are currently in use in mines were published in a handbook. This handbook provides a single information source to help mine operators control dust levels. To date, this handbook has had wide acceptance based on requests and feedback from industry, labor, and regulatory agencies. The handbook is also available on the NIOSH Mining Website.

In addition to major research directed at coal dust control technology, a parallel research effort devoted to improved dust sampling has been ongoing for the past 10 years. Under the Federal Coal Mine Health and Safety Act of 1969, personal gravimetric dust samplers were specified as the instrumentation to be used to monitor compliance with federal dust regulations. These samplers use a size-selective cyclone to collect the respirable fraction of dust on a filter. The mass of dust, pump flow rate, and sampling time are used to calculate an average dust concentration for the shift. This concentration is not determined until the filter has been weighed at MSHA’s Pittsburgh lab several days after the sample is collected. This sampling process has not changed in the past 36 years. In 1999, NIOSH began developing a mass-based, continuous dust monitor that could be worn as a personal dust sampler. This personal dust monitor (PDM), built into the miner’s cap lamp system, provides a running average of dust exposure at any point in the shift, projects an end-of-shift concentration, and provides an actual end-of-shift concentration without any delay. This information will allow mine operators and workers to monitor the dust exposure during the shift. It will empower workers to make changes if it seems that their shift exposure will exceed the standard. The PDM is currently near the end of an extensive field evaluation to assess sampling accuracy, mine worthiness, reliability, and acceptance by mine workers. Results to date are very positive. The PDM is now commercially available.

In 2003, MSHA published proposed changes to its dust sampling program. In these new regulations, MSHA allowed for the use of the continuous PDM. However, industry and labor indicated in public response forums that MSHA should delay rulemaking until the PDM could be further evaluated as a compliance-grade instrument. Both industry and labor envision the PDM as having the potential to become the cornerstone for a new sampling process. Based on stakeholder input, MSHA suspended work on the proposed regulations until additional information on PDM performance is available. A NIOSH report on the latest series of underground and lab evaluations of the PDM is expected to be completed by the end of 2005.