Mining Program Area: Respirable Dust Assessment and Control
The ultimate goal of this research program is to eliminate coal workers’ pneumoconiosis and silicosis from the mining industry. This can be achieved through the development and implementation of control technologies that effectively limit mine worker exposure to airborne respirable dust. In addition, the development of improved real-time or near real-time aerosol monitoring equipment can help reduce worker exposures to hazardous airborne particulate by allowing for more immediate corrective actions in response to overexposures.
Compliance dust sampling data captured by the Mine Safety and health Administration (MSHA) is routinely analyzed to identify the mining occupations that have the highest rates of overexposure to airborne respirable dust. Once identified, the National Institute for Occupational Safety and Health’s (NIOSH) Office of Mine Safety and Health Research (OMSHR) conducts research to quantify the sources of dust exposures for these occupations and then works to identify or develop control technologies that reduce exposures. Also, OMSHR is conducting research to develop instrumentation for mine workers and/or MSHA to more quickly analyze samples for silica content to reduce silica dust exposures in coal and metal/nonmetal mining operations.
Inhalation of respirable coal or silica dust in mining operations can lead to coal workers' pneumoconiosis (CWP) or silicosis, respectively. These are chronic, debilitating lung diseases that can be fatal in their most severe forms. Health surveillance studies of underground and surface mine workers show that these lung diseases continue to be a significant health threat in the mining industry. Within NIOSH’s Division of Respiratory Disease Studies, the Coal Workers' X-ray Surveillance Program gives underground coal workers the opportunity to be examined periodically for the presence of CWP. Data from 2005–2009 x-rays show that 7% of examined mine workers with 25 or more years of mining experience were diagnosed with CWP, Category 1+. During 1998–2007, CWP caused or contributed to the deaths of 8,111 U.S. mine workers. During the same period, the Federal Black Lung Program paid over $8 billion in benefits to coal mine workers and/or surviving widows and dependents. During 2010 and 2011, NIOSH’s Division of Respiratory Disease Studies completed a special program to examine surface mine workers for evidence of CWP. Results showed that 2% of examined surface mine workers were diagnosed with CWP.
Dust control research for the mining industry was initially conducted by researchers in the U.S. Bureau of Mines until this responsibility and expertise was transferred into NIOSH OMSHR. The Bureau research identified many dust control technologies that have been adopted by industry as the foundation of dust control efforts. OMSHR dust control research continues to build upon these dust control capabilities for mining operations. Longstanding cooperation with mining companies, equipment manufacturers, trade associations, labor organizations, and other government agencies has facilitated the development and implementation of control technologies. OMSHR also has unique, full-scale dust galleries that allow for extensive scientific testing of control technologies under controlled conditions, which would be impossible in actual mining operations. After identifying control technologies with promise and optimizing their performance through laboratory testing, these controls can be tested in active mining operations to demonstrate effectiveness in real-world operating conditions.
While reviewing MSHA dust sampling data, it became apparent that respirable dust overexposures are occurring for a number of occupations throughout the various mining commodities. Consequently, OMSHR in-house research projects are addressing dust control issues found in underground coal mining, coal and nonmetal surface mining, and mineral processing operations. In addition to using in-house expertise, OMSHR has ongoing contracts with mining equipment manufacturers and instrumentation companies to take advantage of their experience and capabilities.
The program has made several significant accomplishments and is continuing research to meet its goals; some milestones and highlights are listed below:
- Development of a prototype self-propelled, free-standing respirable dust scrubber for use on continuous miner sections. This unit is designed to remove respirable dust from ventilating air downwind of the continuous miner to reduce the exposure for workers positioned in the return air of the continuous miner. The scrubber is being developed under a contract and should be delivered to OMSHR by the end of 2012.
- Development of a “Helmet CAM” technique for identifying sources of high dust exposures for mobile workers. The technique incorporates a video camera attached to the worker’s hard hat in conjunction with a real-time dust sampler. OMSHR is developing software that allows for direct comparison of the video and dust files to identify high dust sources. This information can then be used to focus development on the most problematic dust sources.
- Quantifying dust levels generated in 20-foot deep cuts with and without flooded-bed scrubbers operating. This information will provide MSHA and mine operators with data that can help them select mining techniques that minimize the respirable dust exposure for workers on continuous mining faces.
- Conducting tests in the full-scale continuous miner gallery to optimize the dust and gas control obtained with flooded-bed scrubbers when a portion of the scrubber exhaust is redirected to the mining face. The goal is to improve airflow patterns at the face and prevent the accumulation of gas, while also improving the dust capture of the scrubber.
- Developing a spray manifold for installation on the tailgate end of a longwall shearer that will provide improved dust control for the tailgate shearer operator and jack setter. The goal is to optimize operating parameters in full-scale longwall gallery testing prior to evaluating the spray manifold on an operating longwall face.
- Using past research conducted on filtration/pressurization systems for enclosed cabs on mobile mining equipment to identify guidelines for installing similar systems on operator booths/compartments in processing operations. We will demonstrate the effectiveness of these systems through evaluations at field sites.
- Developing a portable, mine-worthy silica analysis instrument that can be used at the end of a sampling shift to analyze for the quartz content on filters taken from respirable dust samplers. If overexposures are detected, changes in dust control technologies and/or operating practices can be implemented on the next shift to prevent further overexposures.