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Engineering Controls Database

Guidelines for the Control and Monitoring of Methane Gas on Continuous Mining Operations – Methane Monitoring – Methanometers, Use in Underground Coal Mines

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.
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].
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 and Methane

Engineering controls such as water sprays and scrubbers help maintain safe methane levels in coal mines. Methane monitoring is required to ensure that engineering controls are effective and that methane concentrations do not exceed regulatory standards. NIOSH research examined instruments and sampling strategies used for methane sampling and developed methods for evaluating performance. The research included monitors using both catalytic heat of combustion and infrared absorption sensors.

Methanometers, Use in Underground Coal Mines

The design and use of approved monitors depends partly on whether they are designated as “methane monitors” or “hand-held detectors.”

The methane monitor:
• Is permanently mounted on a mining machine to provide continuous readings of methane levels near the face.
• Is located as close to the face as practicable, but at least 12 inches from roof, face, ribs, and floor [30 CFR 75.342(a)(3) and 30 CFR 75.323(a)].
• Provides a warning signal to alert workers whenever methane concentrations reach 1.0% [30 CFR 75.342(b)(1)].
• Provides an alarm signal to warn workers whenever methane concentrations reach 2.0% [30 CFR 75.342(c)(1)].
• Includes an electrical relay to cut power to the mining machine whenever methane concentrations reach 2.0% [30 CFR 75.342(c)(1)].

The methane detector is:
• Battery powered and portable.
• Used to make 20-minute periodic gas checks at each active mining face [30 CFR 75.362)(d)(1)(iii)] and at outby locations.
• Used to make readings at least 12 inches from the roof, face, ribs, and floor [30 CFR 75.323(a)].

All methane monitors and detectors must be calibrated at least once every 31 days [30 CFR 75.342(a)(4)] according to procedures specified by the monitor manufacturer. All procedures use a standard gas (usually 2.5% methane by volume). Periodic bump tests should be performed between instrument calibrations, which involve exposing the sensor to a calibration gas and recording the concentration displayed on the instrument’s visual readout. Typically, the displayed value should not vary more than 0.2% from the actual concentration of the calibration gas.

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.
CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the Federal Register.

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.

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