There were 37 longwall faces operating in mines in the United States in 2019. The average panel width for these longwalls was approximately 368.5 m (1209 ft). This translates to a range of approximately 170–240 shields per longwall, depending upon the width of shield. The movement of longwall shields is a significant contributor to respirable dust overexposures to longwall operators. Foam is expected to have the potential to reduce this shield dust generation. The foam is applied to the area on the roof between the coal face and the shield tip after the shearer passes. In this study, the longwall shield dust simulator was used to test three foam agents for their ability to control dust from longwall shield movements. Results showed that at low-velocity ventilation (≈ 3.0 m/s (600 fpm)) all foam agents were able to produce dust reduction levels of at least 45%. At high-velocity ventilation (≈ 5.1 m/s (1000 fpm)), the reductions were lower and more variable, ranging from being undeterminable for one foam agent to having 46%–63% reductions for the other two foam agents, with one instance of an increase in dust concentration. Overall, the use of foam agents can provide longwall shield dust control. Important factors are roof coverage and the ability of foam to remain on the roof for extended time periods.

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The National Institute for Occupational Safety and Health conducted a study on leakage rates through underground coal mine seals. Leakage rates of coal bed gas into active workings have not been well established. New seal construction standards have exacerbated the knowledge gap in our understanding of how well these seals isolate active workings near a seal line. At a western US underground coal mine, we determined seal leakage rates ranged from about 0 to 0.036 m3/s for seven 340 kPa seals. The seal leakage rate varied in essentially a linear manner with variations in head pressure at the mine seals.