Explosion risks of bituminous coals in contact with air. Due to molecular hydrogen accumulation in confined spaces (underground mines and ship holds) - A hypothesis study

Bituminous coal piles stored in open air undergo low temperature exothermic oxidation which is accompanied by the emission of small but appreciable amounts of molecular hydrogen, in some cases there is autocatalytic heating (if the heat dissipation from the pile is not efficient). When coal is contained in an confined space at 40°C, accumulation of hydrogen is expected. This emission process has been observed for a wide variety of bituminous coals. Two examples of confined space are: ships' holds and underground coal mines. Israel imports large quantities of bituminous coal from different countries in large ships (in some cases temperatures reach 45-50°C). In Germany deep bituminous coal mines operate mainly in the Ruhr area (in some cases temperatures of the seam reach 60-65°C). Calculations of the amount of hydrogen gas expected to accumulate in the air pocket above the coal cargo in the ship's holds' (assuming that the coal's temperature approaches 40°C during the voyage) or in an cavity adjacent to a coal seam have been performed. The results clearly indicate that in many cases the concentration of the molecular hydrogen can be appreciably above the LEL (lower explosion limit) in air. Thus when storing bituminous coals in a confined space that is in contact with air (e.g. a ship's hold or coal mines) the explosive risk of hydrogen gases should be taken into account, though usually explosions in areas where coal is present are attributed to the presence of dust or methane accumulation.