Carbon and ecological footprints as tools for evaluating the environmental impact of coal mine ventilation air

Coal mines ventilation gases are an important source of methane emissions. Common ventilation systems are designed to ensure safe working conditions in the shafts, leading to huge ventilation gas flow rates. Traditionally, low attention has been paid to such emissions because of their low methane concentration. However, it is necessary to take into account that although the concentration of methane is very low (typically <1%), the volume of air that ventilation systems move is large, and therefore these emissions constitute the largest source of greenhouse gases from underground coal mines. This work proposes the use of ecological and carbon footprints approaches as a tool for determining the relative importance of these emissions in comparison to the other direct and indirect environmental impacts from the coal mining activity. The study has been performed in the main ventilations shafts of the mining company HUNOSA, located at NW Spain (bituminous coal). Results indicate that ventilation air methane is a key fraction of the total emissions of greenhouse gases releases in this activity (60-70%).