In the past 15 years, significant gains in fighting silicosis have been realized across the mining industry, as shown below:

These gains are due in large part to the development of new dust control technology by NIOSH. Of course, new technology was not solely responsible for these improvements. Strong enforcement by the Mine Safety and Health Administration (MSHA) and changing attitudes within the mining industry were vital. Nevertheless, NIOSH made a critical contribution by providing many of the engineering control tools that made these gains possible.

Research on silica controls has involved two unique challenges that made it different from coal dust research. First, a wide variety of industries had a silica problem. This ruled out "one technology fits all" solutions. The second challenge was the low dust levels that had to be attained. It is not unusual to have a mixed dust permissible exposure limit (PEL) of 0.5 mg/m3 or less. These levels can be hard to meet, especially in underground mining.

Over the years, NIOSH has worked to stay ahead of the problem in various ways. MSHA routinely analyzes inspector samples for silica content. NIOSH periodically reviews the MSHA data to identify occupations/areas of excessive silica exposure and refocuses control research in these areas. In this way, the highest exposure occupations in mining are addressed by NIOSH research.

For example, in underground coal mining, occupations that are involved with drilling into rock surrounding the coal seam are typically at the highest silica exposure risk. For roof bolter operators, 25% of samples exceeded the PEL from 1990 to 2004. NIOSH research has shown that roof bolter operators get exposed to silica dust that is released by the roof bolting machine. However, most of their exposure comes from working downwind of the continuous mining machine. Research to provide a clean air source for bolter operators when working downwind of the continuous mining machine has led to the development of a canopy air curtain system. This air curtain is mounted to the underside of the bolter canopies and is above the bolter operator while drilling is ongoing. The air curtain filters a portion of the air entering the bolter entry and blows the cleaned air down over the breathing zone of the bolter operator. Lab testing showed that a 60% reduction in dust (silica) levels could be achieved beneath the air curtain. Results of subsequent underground testing have been promising. A major manufacturer of roof bolters has requested to work with NIOSH to further refine this system for commercialization on its machines.

Another high-risk occupation is that of highwall drill operators at surface mines. During 1990-2004, 36% of samples from these workers exceeded the PEL. To reduce dust for these workers, our research has identified deficiencies in the "Rotoclone" type of dust collector on drills, improved the efficiency and established maintenance procedures for dry collectors, and reduced dust emissions from secondary sources. Significant research has also been done over the last few years to improve the protection given by enclosed cabs on mobile mining equipment. Intervention studies have shown that appropriate filtration systems along with improving cab sealing can reduce dust levels in the cab by 90% or more. Key implementation and operating parameters were identified in this cab research and compiled into a video that shows these parameters. MSHA has placed this video on its website as a tool for mine workers. In addition, NIOSH personnel have worked with a filter manufacturer to develop a new methodology for field testing cab filtration systems for leakage. This test can be done in less than 30 minutes in the field, and a patent application has been filed. This technology will allow mine personnel and mine inspectors to quickly and accurately evaluate the dust (silica) protection provided by cabs.

In processing mills, during 1990-1994, 38% of bagging operator samples exceeded the PEL. As a result of these high exposures, NIOSH conducted research that led to the development of an improved nozzle design for loading bags, a bag and belt cleaner that removes dust from the outside of the bags, an overhead air supply island (OASIS) that provides filtered airflow for workers, and a total mill ventilation system that reduces ambient dust levels throughout a plant. These technologies have been widely accepted and implemented throughout the industry. The bag-filling nozzle has become the standard technology used by the industry, while two different manufacturers are building the bag-cleaning system. These control technologies have been summarized in a compilation of publications on minerals processing dust control that has been widely distributed. In 2002, the Occupational Safety and Health Administration placed this compilation of reports on its website for companies seeking to improve silica dust control. A major manufacturer recently requested copies of this compilation and, at its own expense, had it translated into Spanish for its operations in Mexico.

NIOSH has also developed a new method for cleaning dust from workers’ clothes. A worker’s exposure can increase by as much as 1 mg/m3 from dust liberated by soiled work clothes. For workers in silica sand plants, this means that their silica exposure, just from soiled work clothing, is 10 times over the allowable limit. Currently, MSHA requires that workers use a vacuum to remove dust from their clothing. This method is time-consuming, difficult, and inefficient. Working in partnership with a silica sand plant, NIOSH developed and tested a clothes-cleaning system that uses compressed air nozzles to blow dust from workers’ clothes in a cleaning booth. The worker is required to wear a respirator, goggles, and hearing protection during the process. Field testing at the silica plant showed that the clothes-cleaning booth was 10 times faster and 50% more efficient in removing dust from soiled clothes compared to the vacuuming method. Using compressed air for clothes cleaning is not currently accepted by MSHA. However, the silica sand producer has received a petition for modification with MSHA in order to use this method in its U.S. plants. The company is also pursuing installation of these cleaning booths in its plants abroad. Several other companies are now preparing petitions for modification to allow them to implement the system in their operations.