Abstract: A sealing device for sealing an opening in a shelter (1) against heat action. The walls (9) or ceiling of the shelter comprise several mechanically self-supporting, good thermally insulating layers. The device includes at least one element closing or sealing the opening and a support structure for supporting the element. A locking system and an operating device operating the locking system operate on the element. The element, as seen from the interior of the shelter can be pivoted to the outside and its construction corresponds to that of the wall. The element is held on support arms by the support structure which, from a load standpoint, is independent of the walls in the shelter interior. The locking system is located on the inside of the sealing element and the operating device is accessible both from the inside and from the outside.