Abstract: The invention refers to a method and device for ventilating a device for electron beam irradiation of a web (W), the method comprising the steps of: providing a first chamber (107) comprising a web inlet opening (115) and a web outlet opening (121), providing a second chamber (111) extending inside the first chamber (107), the second chamber (111) comprising a web inlet opening (114), a web outlet opening (112), and an electron exit surface (21) through which electrons are adapted to be emitted into the second chamber (111), passing the web (W) through the second chamber (111), and creating a flow of a gaseous fluid through both the first and second chambers (107, 111) in a direction opposite the direction of travel of the web (W) by supplying said fluid into the web outlet opening (121) of the first chamber (107) and providing at least one outlet (113).