NIOSH Office of Mine Safety and Health Research

Health surveillance studies on underground and surface mine workers show that lung disease from exposure to respirable dust continues to be a major health threat in the mining industry. Coal workers' pneumoconiosis (CWP) is a chronic, debilitating lung disease that can be fatal in its most severe form. The Coal Workers' X-ray Surveillance Program gives underground coal mine workers the opportunity to periodically have a chest radiograph taken to evaluate their lungs for CWP. X-ray data from 2000-2006 shows that nearly 8% of examined miners with 25 or more years of mining experience were diagnosed with CWP. During 1995-2004, CWP caused the deaths of 10,406 U.S. miners. During the same period, the Federal Black Lung Program paid over $12.2 billion in benefits to coal miners and/or surviving widows and dependents.

During 1996-1997, a special silicosis screening program examined 1,236 surface coal mine workers in Pennsylvania. Silicosis, an irreversible and potentially fatal lung disease caused by exposure to excessive amounts of respirable silica dust, was diagnosed in 6.7% of these miners. During 1990-1999, silicosis caused the deaths of 2,405 workers across all industries. A number of states record the workers' industry on death certificates, and the mining industry accounted for 23% of the silicosis deaths reported during 1990-1999. These screening programs indicate that lung diseases are still contracted by miners in both surface and underground mines.

The Mine Safety and Health Administration (MSHA) conducts dust sampling on a periodic basis to determine if mining operations are maintaining dust concentrations below permissible exposure limits. MSHA compliance dust sampling results during 2003-2007 showed that dust overexposures continue to occur for many high-risk occupations in underground and surface coal and noncoal mines. For example, the percentages of inspector samples exceeding the silica exposure levels for selected high-risk occupations are: stone polisher/cutters, 33%; highwall drill operators, 12%; tailgate shearer operators, 32%; jack setters, 20%; continuous miner operators, 19%: and bolter operators,10%. Continued exposure to elevated respirable dust levels and continued development of lung disease indicate that improved dust monitoring and control are needed throughout the mining industry.

Dust Control Technologies

Longwall Dust Control: Longwall personnel can be exposed to harmful respirable dust from multiple dust generation sources including: intake entry, belt entry, stageloader/crusher, shearer, and shield advance. NIOSH conducted ten benchmarking dust surveys at longwall mines representing nearly 25% of U.S. longwall faces to document current dust levels and control technologies. This information was compared to data collected from 1995 to 1999 to document progress and areas of needed research. A paper detailing the findings of this study was presented at the 2010 SME Annual Meeting and has been accepted for publication in an upcoming issue of Mining Engineering. Although recent dust levels show significant reductions, probably related to increased air and water usage, this research has identified that high dust levels outby the shearer are still problematic. The tailgate shearer operator and the return side jacksetter could still benefit from improved control technology to reduce dust levels. NIOSH utilizes many tools including a full-scale longwall dust gallery, computational fluid dynamics programs, and field research to identify, design and test effective control technology.

Tests are being conducted in the full-scale longwall dust gallery at Pittsburgh to evaluate the application of directional sprays on the tailgate end of the shearer to reduce the dust exposure of the tailgate shearer operator and jacksetter. The sprays are used to confine the dust cloud to the face of the coal until it is downwind of job activities. Test parameters include the number of sprays as well as the type, pressure, and location of the sprays for optimal dust control. Preliminary results are promising and a publication is planned for 2012.

The benchmarking study also found that shield dust accounted for 23% of the dust generated by all sources on the longwall face. As longwall production has increased, the number of shields that are advanced and the speed at which they advance has also increased. Shield advance is automated and occurs in much closer proximity to the shearer operators, elevating their dust exposure during head-to-tail passes. Consequently, the respirable dust liberated during shield advance is becoming more problematic. NIOSH has initiated tests in the longwall dust gallery to evaluate spray systems mounted to the underside of the shield canopies with the goal of capturing and redirecting shield dust away from face workers. Future research tasks will investigate the use of foam to control both shearer and shield generated dust, and development of a shearer-mounted scrubber.

Adjusting water sprays during testing in longwall dust gallery.

Continuous Miner Dust Control: Continuous miner section personnel can be exposed to harmful respirable dust from multiple dust generation sources including: intake entry, belt entry, haulageway traffic, feeder/breaker, miner, and roof bolter. NIOSH´s continuous mining dust control project uses the same tools as the longwall project to develop control technology. MSHA inspector data and past NIOSH research directs emphasis on controlling exposures to miner generated dust in the vicinity of cutting and loading and during downwind job activities such as roof bolting.

Effective water spray systems on continuous miners have typically emphasized the confinement and control of the dust cloud in an effort to minimize worker dust exposure. In contrast, water spray systems on miners to control methane gas have generated turbulence and promoted mixing at the face. As a result, water sprays developed mainly for controlling dust are often ineffective for controlling gas and vice versa. A tracer gas injection and monitoring system is being used to evaluate gas levels in the full-scale continuous miner gallery in Pittsburgh while monitoring dust at the same time. Tests were conducted to evaluate the performance of different water spray systems when operated with flooded bed scrubbers during the extraction of extended cuts with exhaust face ventilation. Results of this study were published in the October, 2010, issue of Mining Engineering, which describes components of an optimized system, including the use of blocking sprays mounted on the sides of the miner help to control dust and methane levels, particularly when the miner is in the slab cut position. During the next two years, NIOSH plans to test the redirecting of scrubber airflow towards the face to control dust. This technique allows the curtain to be maintained at a more inby position, which may lower the dust exposures of persons working in the vicinity of the miner.

Wet-head spray technology.

NIOSH has conducted baseline dust surveys in six underground coal mines to evaluate dust levels generated throughout extended cut faces. Real time sampling was conducted and combined with time study information to quantify dust levels as the continuous miner and roof bolter progress through their extended cuts. Operational performance of the flooded bed scrubbers on miners and the dust collection system on roof bolters were also monitored during these cuts. Survey results are analyzed and published in a 2011 NIOSH Report of Investigation 9680. The study found that, when using a deep-cut ventilation configuration, mines were able to extend the cuts from 20 to 40 ft without negatively impacting the dust exposures of face workers. Phase II of this project will be conducted in 2011 at mines using exhausting face ventilation and will compare the dust exposures of face workers when using deep-cutting methods, consisting of a scrubber and greater curtain setbacks, to levels using standard curtain setback distances without the scrubber operating.

Roof bolter operators are subjected to dust generated by the bolter machine and dust generated by the continuous miner when working downwind of the miner. For bolter-generated dust, laboratory tests were conducted to evaluate the potential dust reduction that may result from the use of water boxes that can be installed on the discharge of the vacuum dust collection system used on roof bolters. Sampling dust concentrations upwind and downwind of a water box indicated that the box reduced dust levels in the dust collector exhaust by approximately 40% in laboratory testing. Results from this study were presented at the 2010 SME Annual Meeting and will be published in an upcoming issue of Mining Engineering or in SME´s 2011 Transactions. In addition, NIOSH is currently evaluating data from two laboratory experiments that examined the 1) use of a bit collar for controlling bolter generated dust, and 2) use of a redesigned canopy air curtain to create a clean breathing zone for roof bolters. Publications for these studies are planned for 2012. Future plans include assisting a roof bolter manufacturer in the development of a standalone dust collector to clean dust laden intake air and direct clean air over the bolter operators.

Surface Mining Dust Control: MSHA inspector data collected at surface coal mines from 2001 through 2010, emphasize a need to focus on blasthole drill dust control since samples collected on the drill operator, drill helper and blaster occupations exceeded the quartz dust standard at surface coal mines 29%, 21% and 15% of the time, respectively. NIOSH evaluated modifications to the drill shroud in an effort to improve the capture of drill-generated dust. A physical barrier is mounted on the inside of the drill shroud to help confine dust within the shroud and allow for greater capture by the drill dust collector. Laboratory and mine site tests have shown that this system can reduce dust escape from the drill shroud, lowering dust levels in areas around the drill by 66 to 81%. Results from this study were published in the March, 2011, issue of the International Journal of Mining, Reclamation and Environment.

MSHA and operator samples also indicate dust exposure problem areas associated with mobile surface workers such as mechanics, laborers, utility, and clean-up persons. Assessing the exposure of mobile workers in the past has been difficult because their work duties are not confined to a particular area or activity. NIOSH developed a software application and sampling technique called Enhanced Video Analysis of Dust Exposures (EVADE) to address this problem. EVADE synchronizes real-time respirable dust exposure data to video collected from a helmet-mounted camera, allowing an accurate assessment of the contribution of various activities on the overall exposure for the individual. This technology will be instrumental for designing effective dust control strategies. EVADE is currently being used by NIOSH to assess the exposures of mobile surface workers and occupations within the metal/nonmetal mining industry. NIOSH plans to release the EVADE software and a user manual (Information Circular) as a package to the mining industry within the next two years. It can be used by mining professionals to conduct self-assessments of dust problems and as a training aid to demonstrate proper operating procedures to minimize exposures.

Since haul road activity has been identified as the largest contributor to dust generated at surface mining sites, it is reasonable to assume that this source will be a significant component of exposure for mobile surface workers. In 2011, NIOSH plans to evaluate a new water truck application technique based on ground speed instead of engine rotation that may improve dust control by eliminating under-watering conditions.

Metal/NonMetal Dust Control: MSHA and operator samples collected at metal/nonmetal mining facilities and surface coal mines consistently demonstrate that occupations with operator cabs typically have some of the highest history of noncompliance with the dust standard. Methods were needed to field test the integrity of the cabs and to improve the understanding of effective cab design and maintenance. Past NIOSH research has determined critical design components for effective cab filtration systems. Based on this research, an equipment manufacturer designed a system to incorporate these components. In 2011, NIOSH completed a long term evaluation of the system and recommended changes to simplify maintenance without compromising air cleansing efficiency. Results of this study will be presented at the 2012 SME Annual Meeting. Also occurring in 2011, NIOSH is publishing a Report of Investigation describing a new test method to determine outside air leakage into cab filtration systems that can be conducted in the field, eliminating the need to test cab integrity in a chamber. This system was developed by NIOSH and Clean Air Filter and has been patented in the U.S., Canada and Australia. Having a field test option will likely lead to greater adoption by the mining industry and earlier identification of cab filtration failures. Future work in the metal/nonmetal area will include adapting cab filtration technology for control of dust in control rooms, and the development of improved dust control technology for bagging operations and dimension stone shops.

NIOSH is also working in cooperation with the Industrial Minerals Association - North America (IMA-NA) to complete a handbook designed for use by industrial minerals producers. The handbook contains detailed information on control technologies to address all stages of the mineral processing and mining, including drilling, blasting, crushing, milling, screening, conveying, transporting, bagging and bulk handling operations. It is planned for release as a NIOSH Report of Investigation in the last quarter of 2011.

Dust Monitoring Technologies

The goal of the monitoring program is to develop and evaluate various instruments that can be used to assess worker exposure to respirable particulate matter on a real-time or near real-time basis. Real-time particulate monitoring can be used to effectively locate areas where dust liberation is elevated and determine how well implemented controls are working. Real-time instruments can enable workers and management to assess if exposure levels are acceptable and encourage corrective action before full-shift exposures exceed allowable limits. In addition, these types of instruments could potentially be used by MSHA for compliance purposes to ensure that particulate levels are within acceptable limits.

Personal Dust Monitor

NIOSH developed a personal dust monitor (PDM) to measure personal exposure to respirable dust in coal mines. The personal dust monitor combines the dust sampler and cap lamp into one unit. Extensive laboratory and in-mine testing of the new monitor have demonstrated that the device accurately measures workers´ exposure to dust in mine environments. Unlike the existing filter sampling system that can take days or weeks to know a particular day´s results, the PDM real-time display provides mine workers, managers, and health specialists with immediate knowledge of mine dust exposure levels. This immediate feedback of dust exposure provides a connection between work activities and dust levels and permits action to be taken in a timely fashion to prevent overexposures.

Personal dust monitor.

Side-by-side testing of the PDM with the gravimetric sampler currently used by MSHA and industry has demonstrated the equivalency between the two samplers. Further work was conducted by NIOSH to study how miners responded to the PDM from an ergonomic and general understanding perspective. Results showed that most miners liked the PDM sampler over the current sampler. Many miners were able to use the screen information to reduce dust exposures. In addition, NIOSH has developed a software package that can be used by mine operators to facilitate analysis of PDM data.

Silica Monitoring

As originally developed, the filter within the PDM could not be used to conduct silica analysis on the collected dust. NIOSH is currently evaluating an appropriate filter material and filter containment system that would allow PDM filters to be sent to MSHA for silica analysis in a process similar to the procedures used with the current gravimetric samplers.

NIOSH is also continuing research to investigate analytical technologies that may lead to the development of an end-of-shift monitor that can complete an on-filter analysis for silica content in a short time frame. The goal is to have this instrument available to MSHA inspectors so that a silica determination can be made at the end of the working shift. If the sample shows that allowable limits are being exceeded, changes to the dust control measures or operating practices can be made on the next shift to prevent further overexposures.

Finally, NIOSH is initiating research into a real-time silica monitor. This silica monitor would be used to continuously monitor silica exposure levels in the work environment. This immediate feedback of silica exposure provides a connection between work activities and silica concentrations and permits action to be taken in a timely fashion to prevent overexposures.