An upcast shaft is the vertical opening through coal mine strata designed to pull stale air and gases out of the mine. Upcast shafts can also be equipped with cages and used for the conveyance of men and machinery in the mine. The returning gallery is a tunnel through which air passes from the inner workings of the mine to the upcast shaft. When a coal fire is lit at the bottom of an upcast shaft the hot air created by the fire is pulled through the dumb pit and exits the upcast shaft to the mines surface -- while cool air is drawn in through the downcast shaft.