Engineering Controls Database
Guidelines for the Control and Monitoring of Methane Gas on Continuous Mining Operations – Moving Air to the Mining Face – Maintaining Curtain/Tubing Setback Distance
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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 ore-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 ore 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. Most mining accidents today generally involve only a few individuals. However, the infrequent occurrence of gas explosions puts the lives of the entire underground workforce at risk. 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]. |
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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. Moving Air to the Mining Face Effective face ventilation requires that a sufficient quantity of intake air be delivered to the mining face in order to dilute liberated methane to a safe level. Federal regulations include the following requirements: • Face ventilation control devices shall be used to provide ventilation to dilute, render harmless, and to carry away flammable, explosive, noxious, and harmful gases, dusts, smoke, and fumes [30 CFR 75.330]. • A minimum quantity of air (3,000 ft3/min) is required at each face area [30 CFR 75.325]. A mine operation must specify in its ventilation plan the minimum quantity of air required to maintain methane levels below 1% at their working faces. Early USBM research examined ways to deliver air to the end of the curtain or tubing with minimal losses. Recent NIOSH research has examined more effective ways to move air from the end of the curtain to the face. New monitoring instruments and sampling techniques made it possible to examine how operating conditions affect airflow inby the curtain or tubing. Maintaining Curtain/Tubing Setback Distance Regulations [30 CFR 75.330] require that curtain and tubing be installed no greater than 10 ft from the point of deepest face penetration unless another distance is approved in the ventilation plan. Most mines using blowing ventilation are granted permission to increase setback distance to 20 ft. During deep cutting, it is more difficult to keep the end of the curtain or tubing close to the face without interfering with the mining operation or exposing workers to an unsupported roof. Earlier work examined how extensible curtain or tubing systems could be advanced manually to keep setback distances less than 10 ft. With these systems, leakage at the roof was a problem, they were labor intensive, and their use required periodic interruptions of the cutting sequence. Several techniques for automatically advancing the ventilation system were proposed but never tested underground. One design deployed spiral reinforced tubing from the mining machine as it advanced into the coal face (Figure 1). A take-up device, similar to a shuttle car reel, could maintain constant tension on a cable that supported the tubing, causing it to retract as the machine backs away from the face. Another proposed technique that was tested in the laboratory used light-weight nylon tubing released from an auxiliary fan [Goodman et al. 1990]. Air pressure inflated the tubing as it moved away from the fan in the direction of the face. The tubing was manually pulled from the face when mining was completed.  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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Goodman GVR, Taylor CD, Divers ED [1990]. Ventilation schemes permit deep advance. Coal, October, pp. 50–53. 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. 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 |