Gas content: probabilistic method

The probabilistic method was implemented due to the inconsistency of the gas content of a coal seam in different sections and problems encountered in obtaining a full sample of undisturbed coal to get accurate measurements. This method uses a large number of coal samples, which can be as few as 20 but 50 is more accurate, with the mass of each sample in the range of 25 – 40 grams. These samples are crushed in a sealed bomb and the gas content for each is determined and graphed as frequency vs. gas content. In general, the upper 90 percentile is recorded as the in-situ gas content of the seam but in more gassy seams the upper 95 percentile can be taken to provide a more accurate measurement.