Mining Project: Controlling Respirable Dust in Coal Mining Operations

Research Summary

Health surveillance data indicate that overexposure to respirable dust in the nation’s coal mines continues to lead to the development of lung disease. The disease is present in the current workforce, with results from the most recent NIOSH Coal Worker’s X-ray Surveillance Program (CWXSP) indicating that eight percent of miners with at least 25 years of experience show evidence of pneumoconiosis.

To address this problem, this project developed control technologies to reduce respirable dust exposures and preserve the health of mine workers in all coal mining settings—i.e., longwall, continuous, and surface mining. This project specifically targeted those coal mining occupations where Mine Safety and Health Administration (MSHA)compliance data indicate the highest exposures to respirable dust.

This project had five research aims, with outcomes, as follows:

Aim 1: Investigate the use of longwall shearer-mounted water-powered dust collectors to reduce dust exposures.

Outcome: Laboratory testing on a longwall shearer fan-powered, flooded bed scrubber designed by the University of Kentucky's Mining Engineering Department was conducted by NIOSH at the Pittsburgh Mining Research Division (PMRD) longwall dust gallery. Results showed that the scrubber reduced respirable dust by 56% in return airways and by 74% in the walkway next to the shearer (Arya et al. 2018). High airflow (13,700 cfm) through the scrubber provided the greatest dust reductions, indicating that NIOSH would have to maximize the airflow capability of water powered scrubbers in its research efforts. Water powered scrubber testing continues in the project, Improved Float Dust Controls in Underground Coal Mines.

Aim 2. Develop underside canopy spray systems to reduce dust generated by spalling along the longwall face.

Outcome. Underside shield sprays were tested in the laboratory. Results showed significant reductions of respirable dust to personnel in longwall walkways.  Use of underside shield sprays with splitter arm sprays improved dust reductions over just splitter arm sprays alone. Optimum parameters for underside shield spray placement were determined, as follows (Klima et al. 2020):

• 75-degree sprays with a 4.5-ft distance from the face was optimum for the upwind splitter arm and drum centerline locations (over 90%).
• Downwind towards the tailgate, 60-degree sprays were better (63% to 85% reductions) at about the 4.5-ft to 5.0-ft locations.
• Higher water pressure (200 psi) improved performance.

Aim 3: Develop foam applications to the longwall roof to mitigate dusts associated with shield advance.

Outcome: Laboratory testing of foam to control respirable dust generation from longwall shield advance was completed with the following results: 

• Compressed air foam had a 10-19 expansion ratio, while blower air foam had a 30–60 expansion ratio.
• Compressed air foam roof coverage after 3 minutes resulted in 94%-98% coverage for foam agents B and A.
• Compressed air foam roof coverage after 30 minutes was 20% and 90% coverage for foam agents B and A, respectively (Reed et al. 2017).
• Blower air foam roof coverage after 30 minutes was 74%-92% for foam agent A and 3%-50% for foam agent B. Compressed air foam was easier to apply, but wetter in that blower foam requires larger-diameter hoses (2”) (Reed et al. 2017).

Though the results are not yet published, NIOSH field reports to several chemical companies that partnered on this research have indicated that foam was shown to be a better agent for dust reduction of longwall shield dust than water in simulated shield advance.  Water was not suitable for dust control, with an increase in dust concentrations when used on longwall shield dust. The cause is thought to be due to the inability to saturate the material on top of the longwall shield. The water only provides dampness, which seems to exacerbate the dust concentrations from this source. All foam agents produced reductions at low velocity (600 fpm), while higher velocities produced variable results for only two agents.

Field testing of foam at longwall operations was not completed due to time and personnel constraints.

Aim 4: Investigate operating parameters to reduce shuttle car operator exposure in blowing face ventilation, including the use of a canopy air curtain to reduce respirable coal mine dust exposures for shuttle car operators.

Outcome: Lab testing was completed in the continuous mining gallery at PMRD.  Testing showed the optimum parameters for blowing face ventilation system were a 50-ft curtain setback with 12,000 cfm face ventilation while the continuous miner was operating side-body-mounted blocking sprays (Klima et al. 2019). Lab testing of a shuttle car canopy air curtain demonstrated up to 80% reductions for respirable dust to the shuttle car operator.  High-ventilation velocities decreased the reduction (Reed et al. 2018). 

Shuttle car airflow field testing at two mining operations showed that high ventilation may not be as problematic as previously thought.  High dust concentration areas were at the continuous miner and feeder locations, not while tramming.  These two (continuous miner and feeder) areas have lower ventilation velocities (Shahan et al. 2018, Reed et al. 2019. Field testing was completed with the results to be published soon.

Aim 5. Evaluate a stand-alone dry scrubber to reduce dust exposures on continuous mining sections.

Outcome: Laboratory testing of the dry scrubber showed that dry scrubber respirable dust reductions of up to 95% were achieved.  The scrubber was able to maintain consistent airflow at 3,000 and 9,000 cfm as targeted in the studies. However, noise was an issue with the dry scrubber approaching 90 dB(A) when filters were loaded.  Field testing showed that respirable dust reductions of approximately 50% were achieved when operating downstream of a continuous miner (Organiscak et al. 2017, Klima 2017).

Based on this project research, it is expected that industry will adopt validated interventions in order to comply with more stringent respirable dust standards contained in the MSHA's final rule, Lowering Miners' Exposure to Respirable Coal Mine Dust, Including Continuous Personal Dust Monitors. Assuming industry adoption, reduced respirable dust levels in the workplace will correspondingly decrease the incidence and prevalence of respiratory illnesses in coal miners.

References

Arya, S., Sottile, J., Rider, J. P., Colinet, J. F., Novak, T., & Wedding, C. (2018). Design and experimental evaluation of a flooded-bed dust scrubber integrated into a longwall shearer. Powder Technology, 339, 487–496. https://doi.org/10.1016/j.powtec.2018.07.072

Klima, S., Reed, W.R., Driscoll, J., and Mazella, A. (2020) Laboratory investigation of underside shield sprays to improve dust control of longwall water spray systems. 2020 SME Annual Meeting and Exhibit, Phoenix, AZ, Feb 23-26, 2020. Pre-print 20-052.

Reed, W. R., Zheng, Y., Klima, S., Shahan, M. R., & Beck, T. W. (2017). Experimental study on foam coverage on simulated longwall roof. Transactions of the Society for Mining, Metallurgy & Exploration, 342 (August 2017), 72–82. https://doi.org/10.19150/trans.8110

Klima, S. S., Organiscak, J. A., & Colinet, J. F. (2019). Reducing Shuttle Car Operator Dust Exposure by Improving Continuous Miner Blowing Face Ventilation Parameters. In SME Annual Meeting 2019, Feb. 24-27, 2019 (pp. 1–9). Denver, CO.

Shahan, M., Reed, W. R., Yekich, M., & Ross, G. (2018). Field investigation to measure airflow velocities of a shuttle car using independent routes at a central Appalachian underground coal mine. Mining Engineering, 70(11), 41–47. https://doi.org/10.19150/me.8601

Reed, W. R., Shahan, M., Ross, G., Singh, K., Cross, R., & Grounds, T. (2019). Field investigation to measure airflow velocities of a ram dump car using circular routes at a Midwestern underground coal mine: a case study. Environmental Monitoring Assessment. https://doi.org/10.1007/s10661-019-7624-8

Organiscak J., Noll J., Yantek D., Kendall B. (2017). Examination of a newly developed mobile dry scrubber (DS) for coal mine dust control applications. 2016 Transactions of the Society for Mining, Metallurgy & Exploration, Vol. 340, pp. 38-47.

 Klima, S. (2017). Mobile dry scrubber provides cleaner air for downwind roof bolter. NIOSH Tech News 559. DHHS (NIOSH) Publication No. 2017–208. Pittsburgh, PA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, NIOSH, Pittsburgh Mining Research Division.