Lightning propagation through the Earth and its potential for methane ignitions in abandoned areas of underground coal mines

Strong circumstantial evidence suggests that lightning has initiated methane explosions in abandoned and sealed areas of underground coal mines. The US Mine Safety and Health Administration investigated several of these occurrences within recent years. The investigated explosions occurred at significant depths ranging from 500 to 1200 ft. Data from the National Lightning Detection Network indicate a definite correlation between the times and locations of the explosions with those of specific lightning strikes. This paper addresses the question, "Can lightning cause potential differences capable of igniting methane-and-air mixtures at overburden depths at which underground coal mining occurs?" A mine depth of 600 ft was selected for this initial study. Computer simulations were performed, with and without the presence of a metal-cased borehole extending from the surface to the mine level. CDEGS software from Safe Engineering Services & Technologies, Ltd. was used for the simulations.