On a continuous miner coal face methane concentrations are affected by the quantity of fresh intake air reaching the face. When mining the box cut on a 12.2-m (40-ft) two-pass extended cut face, the continuous miner is always at the point of deepest penetration, and operation of the machine-mounted dust scrubber and water spray system improve the flow of fresh air to the end of the box cut. However, when the continuous miner leaves the box cut to begin cutting the 40-ft slab, little is known about how much ventilation air reaches the end of the box cut. The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health conducted a full-scale study to answer this question. Tests were run to determine how much ventilation air reaches the end of the box cut with the continuous miner at three locations in the 40-ft two-pass extended cut mining sequence; at the end of the 40-ft box cut, at the start of the 40-ft slab cut, and 6.1 m (20ft) into the slab cut. During these tests, methane gas was uniformly released at the end of the 40-ft box cut. Methane concentrations measured 0.3 m (1 ft) from the roof and face of the box cut were used to estimate face airflow quantities. Fresh airflow rates of 1.89 and 4. 72 m3/sec (4,000 and 10.000 cfm), scrubber flow rates of 0, 4,000 and 10,000 cfm, water spray pressures of 0 and 827 kPa (0 and 120 psi), and a blowing curtain setback position of 15.2 m (50ft) were used during these tests. To improve ventilation to the end of the 40-ft box cut when the continuous miner was starting the 40-ft slab cut and 20ft into the slab cut, the blowing curtain was advanced from its 50-ft setback to locations 40-ft and then 8.5 m (28ft) from the face
