As disclosed in my U.S. Pat. No. 4,256,944, the present invention likewise envisions the utilization of an exhaust system 60, shown schematically in FIG. 5, by which gases such as methane, water vapor, etc., released by the material being thawed are exhaused from the microwave cavity formed by the shielding hood 10 and the rail car 12 during a heating, thawing and/or demoisturing operation.