Impact of mine closure and access facilities on gas emissions from old mine workings to surface : examples of French iron and coal Lorraine basins

Abstract : Closure methods and techniques of mine shafts located in the iron Lorraine basin, in the Lorraine and in North-East coal basins are quite different. For the first, they are associated with adits. Some are closed by a simple grid to avoid entrance in mine workings but gas entrance and exit are allowed. Coal shafts are secured and can be equipped with a vent to enable mine gas outflow in specific conditions. Measurements stations were installed on mine accesses to monitor mine gas parameters (oxygen, carbon dioxide and methane volumetric content, radon volumetric activity, flow velocity, gas temperature and differential pressure) and external parameters (temperature and barometric pressure). The results show that gas flow can be regulated mainly by temperature gradient between external atmosphere and mine workings (in iron mines) or by barometric pressure (in coal mines). Gas emissions from iron mines may require extra securing protocol that prevents population exposal to noxious gas.