Engineering Controls Database
Guidelines for the Control and Monitoring of Methane Gas on Continuous Mining Operations – Effect of Water Sprays on Face Airflow and Methane – Effect of Water Sprays on Airflow at the Face
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The introduction of conventional mining methods, which increased the rate of mining, was an important step in the mechanization of mining. The intermittent nature of the conventional mining process halted the extraction process for coal-loading and usually allowed time for methane gas to be dispersed. However, the introduction of continuous mining machines in the 1940s produced a constant flow of coal from the working face of the mine and resulted in an increase in methane levels. The number of face ignitions increased as more continuous mining machines were placed underground. Methane levels were found to be dangerously high. In some cases, methane concentrations measured 20 ft from the mining face exceeded the lower explosive limit (5% by volume) [USBM 1958]. The need for better face area ventilation was recognized to reduce the potential for explosions. |
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Excessive levels of methane gas can affect the safety of the underground work force. Available methane control systems have been challenged in recent years by mining developments which include the use of continuous mining machines. In the past 10 years, explosions have led to 65 fatalities and 18 injuries with major explosions occurring at the Sago Mine in West Virginia in 2006 (12 fatalities and 1 injury), the Darby No. 1 Mine in Kentucky in 2006 (5 fatalities and 1 injury) and, most recently, at the Upper Big Branch Mine in West Virginia in 2010 (29 fatalities) [NIOSH 2011]. The occurrence of a methane gas explosion puts the lives of the entire underground workforce at risk. |
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The U.S. Bureau of Mines (USBM) was formed in 1910 following a series of underground explosions that resulted in many fatalities and injuries [Kirk 1996]. The agency was responsible for conducting scientific research and disseminating information on the extraction, processing, use, and conservation of mineral resources. The USBM research program for mining health and safety was transferred to NIOSH in 1996. Since that time, NIOSH has established a ventilation test gallery where techniques for methane control and monitoring are evaluated under a variety of conditions that simulate airflow near the working face of a continuous mining section. Airflow patterns and methane concentrations are studied in a detailed manner that is not possible in a working underground mine. Effect of Water Sprays on Face Airflow Machine-mounted water spray systems are used primarily for dust control. The water delivered through the spray nozzles wets the coal and helps prevent suspension of dust. However, Kissell [1979] demonstrated that water sprays act as small fans and move air. This airflow helps dilute and remove methane from the face area. Water sprays can be grouped to direct airflow across the mining face. These “spray fan systems” are now installed on many mining machines. Research conducted in the ventilation test gallery examined how sprays installed on the mining machine affect airflow patterns and methane distributions in the face area [Chilton et al. 2006]. Air velocities were measured concurrently at two locations at the face—the curtain side (location 1) and the off-curtain side (location 2) (Figure 1). To simplify the comparisons, the component of the velocity moving perpendicular to the face was calculated for each test. By convention, an airflow moving away from the face was given a negative velocity. Figure 2 shows velocities measured with no sprays operating.   • With no sprays operating, flow was toward the face on the off-curtain side of the face (location 2) and away from the face on the curtain side of the face (location 1). • Flow moved from right to left across the face and increasing intake flow increased air velocities moving toward and away from the face but did not affect the flow pattern. With the sprays operating, flows were measured at the curtain side (location 1) and off-curtain side (location 2) of the face (Figure 3).  Location 1: Curtain (intake air) side of the face • The use of water sprays reversed the direction of the airflow on the left (curtain) side of the face (i.e., flow moved toward the face). • Increasing the water pressure increased velocity. • Velocities were higher when the angled sprays were used. • Increasing intake airflow had only a small effect on face air velocity. Location 2: Off-curtain (return air) side of the face • Airflow direction, toward and away from the face, varied o With straight sprays, airflow moved toward the face. o With angled sprays, airflow moved away from the face. • Increasing the water pressure increased velocity. The straight and angled sprays created different flow patterns at the face. • With angled sprays o Air moved toward the face on the left (curtain) side of the entry and away from the face on the right (off-curtain) side. o Air moved left to right across the entire face. • With straight sprays o Air moved toward the face on the right and left sides of the entry. o Air did not move across the entire face but moved over the top of the machine and away from the face. The movement of water mist over the machine gave evidence of this flow pattern. NOTE: The above control information is taken directly from the following publication: NIOSH [2010]. Information circular 9523. Guidelines for the control and monitoring of methane gas in continuous mining operations. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2010-141. |
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Chilton JE, Taylor CD, Hall EE, Timko RJ [2006]. Effect of water sprays on airflow movement and methane dilution at the working face. In: Mutmansky JM, Ramani RV, eds. 11th U.S./North American Mine Ventilation Symposium. Leiden, The Netherlands: Taylor & Francis/Balkema, pp. 401–406. Kirk WS [1996]. The history of the Bureau of Mines. In: U.S. Bureau of Mines Minerals Yearbook, 1994. Washington, DC: U.S. Bureau of Mines. Kissell FN [1979]. Improved face ventilation by spray jet systems. In: Proceedings of the Second Annual Mining Institute. Tuscaloosa, AL: University of Alabama. NIOSH [2011]. Ventilation and explosion prevention highlights. [http://www.cdc.gov/niosh/mining/highlights/programareahighlights16.html] USBM [1958]. Auxiliary ventilation of continuous miner places. By Stahl RW. Washington, DC: U.S. Bureau of Mines, Report of Investigations, No. 5414. |
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coal mining continuous mining operations deep-cut mining miners |
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| Directing spray nozzles toward the return side of the face increases the velocity of airflow across the face. |