Pittsburgh, PA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 99-138, (RI 9648), 1999 Aug; :1-16
Methane concentrations at a continuous mining machine coal face are affected by the quantity of fresh intake air reaching the face. During the mining of the box cut on a 40-ft two-pass extended-cut face, the continuous miner is always located at the point of deepest penetration, and operation of the machine-mounted dust scrubber and the water spray system improve the flow of fresh air to the face of the box cut. However, after the continuous miner leaves the box cut to begin the cutting of the 40-ft slab, little is known about how much ventilation air reaches the face of the box cut during the slab cut. The Pittsburgh Research Laboratory of the National Institute for Occupational Safety and Health conducted a study to answer this question. Tests were run to determine how much ventilation air reaches the face of the box cut, with the continuous miner at three locations in the 40-ft two-pass extended-cut mining sequence. These three locations were at the end of the 40-ft box cut, at the start of the 40-ft slab cut, and 20-ft into the slab cut. During these tests, methane gas was released at the face of the 40-ft box cut to simulate methane liberation underground. Methane concentrations measured 1-ft from the roof and face of the box cut were used to estimate face airflow quantities at fresh air flow rates of 10,000 and 4,000 cfm, scrubber flow rates of 0, 4,000 and 10,000 cfm, and water spray pressures of 0 and 120 psi. A blowing ventilation curtain setback position of 50-ft was used during these tests. With the continuous miner operating at the face of the 40-ft box cut, and the blowing ventilation curtain maintained at 50-ft, at least 50% of the available fresh air was delivered to the face when the scrubber and water spray system were operating. The operation of the scrubber was essential to providing this quantity of air to the face for all test conditions, while the operation of the water sprays was significant only at the lower fresh air flow rate of 4,000 cfm. With the continuous miner operating at the start of the 40-ft slab and the blowing ventilation curtain remaining at 50-ft, fresh airflow to the face of the 40-ft box cut was significantly reduced-in some cases to <10% of the available fresh air. Operation of the scrubber and/or the water sprays resulted in no significant improvement in the ventilation at the face of the box cut. When the continuous miner advanced 20-ft into the slab cut, an improvement was achieved in the quantity of air reaching the face of the box cut. with the quantity increasing by 100% or more of what it was for similar conditions at the start of the 40-ft slab. To improve ventilation to the face of the 40-ft box cut when the continuous miner was starting the 40-ft slab cut, and operating at 20-ft into the slab cut, the blowing ventilation curtain was advanced from its 50-ft setback location to locations 40-ft and then 28-ft from the face. With the continuous miner at the start of the 40-ft slab, extending the curtain 10-ft resulted in increases in fresh air to the face of the box cut of 53% to 159% depending on the fresh air flow rate. The additional 12-ft extension resulted in increases of 270% to 626%.