The displacement of asphyxiating, toxic and/or potentially explosive gases such as carbon dioxide, carbon monoxide and methane from a coal mine goaf into the working environment The mixing of coal dust with air, creating a potentially explosive mixture The overpressure wave can throw objects into people, knock people over (and potentially throw people into stationary objects or even into automated machinery), knock miners' helmets off, pepper the flesh with gravel or small rocks, stop or alter the normal ventilation of the mine and move large items of machinery, in some cases violently.