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Engineering Controls Database

Guidelines for the Control and Monitoring of Methane Gas on Continuous Mining Operations – Moving Air to the Mining Face – Estimating the Ventilation Flow Quantity reaching the Face

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.
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 Jim Walter Resources No. 5 Mine in Alabama in 2001 (13 fatalities and 3 injuries), 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.
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.

Estimating the Ventilation Flow Quantity Reaching the Face

The quantity of intake air directed to a mining face is usually measured at the mouth of the ventilation tubing or curtain, but the quantity of intake air reaching the face cannot be precisely measured. The further the curtain or tubing mouth is from the face, the greater the uncertainty about the quantity of air reaching the face.

Tests were conducted in the ventilation test gallery [NIOSH 1999] to estimate the quantity of air delivered to a mining face when using blowing curtain and the following operating conditions:
• Machine at the end of box cut face (A in Figure 1)
• Machine at the beginning of slab cut (B in Figure 1)
• Blowing curtain with 50-ft setback.
• 4,000 or 10,000 ft3/min measured at mouth of curtain.
• Scrubber off or at flow equal to intake flow.
• Spray on whenever scrubber was operating.

Methane gas was released from the face manifold at a known flow rate and measured at three locations (Figure 1) that were 1 ft from the roof and the face. The estimated flow (ft3/min) reaching the face was calculated using measurements of methane flow rate through the manifold, the average face concentration, and the intake flow rate.

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.
Figure - 1 - Mining machine locations for measuring face airflow.

Figure - 1 - Mining machine locations for measuring face airflow.
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 [1999]. Evaluating the ventilation of a 40-foot two-pass extended cut. By Thimons ED, Taylor CD, Zimmer JA. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, NIOSH Report of Investigations, No. 9648.

NIOSH [2011]. Ventilation and explosion prevention highlights. []

USBM [1958]. Auxiliary ventilation of continuous miner places. By Stahl RW. Washington, DC: U.S. Bureau of Mines, Report of Investigations, No. 5414.
coal mining
continuous mining operations
deep-cut mining
The results indicated that use of a water spray and scrubber had a significant effect on airflow reaching the face only when the mining machine was located at the face (Figure 1).
• When the machine was at the end of the box cut (location A) and the scrubber and sprays were operating, more than 50% of the available air reached the face.
• When the machine was at the beginning of the slab cut (location B) and the scrubber and water sprays were operating, only 5% to 14% of the available air reached the face.