In HBL (Lorraine coalfield), large amounts of air are used in order to dilute methane in retreat coalfaces. A parasite flow of air exists in the goaf, leading to the risk of spontaneous combustion of remaining coal as well as to a diminution of firedamp drainage efficiency. The evaluation of various means for reducing this flow has been done through the use of models : a physical model and a numerical model based on a CFD package. The efficiency on air leakage reduction, decrease of methane concentration in the air return or increase of methane concentration of drainage has been quantified for one or more stoppings set up in the abandoned gates or for their backfilling. The influence is small but positive as regards drainage efficiency improvement but almost zero on risk mitigation of spontaneous combustion in the goaf.
