Abstract: In order to ensure that flue gases will not escape from an enclosure (1) which contains a metallurgical vessel (2) as charging boxes (10) are moved into and out of the enclosure, the charging crane (14) is disposed inside the enclosure (1) and the enclosure contains at least one lock chamber (11), which is adapted to contain a charging box (10) in a stand-by position and which adjoins a charging opening (9) that is formed in a side wall (5) of the enclosure. A top wall of the lock chamber is formed with an opening (12), which is adapted to be closed and through which a charging box can be moved between the lock chamber and the main part of the interior of the enclosure.