A method and a filter device for the dry filtration of a gas flow carrying foreign objects in a filter device for purifying waste gas produced in additive manufacturing technologies, conducting a raw gas flow containing foreign objects into a raw gas space of a filter unit having at least one filter surface separating a raw gas side from a clean gas side, feeding oxidant to a reaction region located on the raw gas side of the filter surface downstream of the filter surface, such that foreign objects contained in material cleaned off from the filter surface and/or in the raw gas flow react with the oxidant in the reaction region to form foreign objects containing oxides.