An assembly for securely enclosing an opening defined by a building structure comprising a frame sized to be disposed to substantially surround the opening and engage the structure and a panel pivotally securable to the frame and sized to substantially cover the opening, the panel having a front and a back. Locking means for selectively locking the panel to the frame in a closed position and unlocking the panel so that it can be pivoted to an open position, the locking means comprising selectively an internal locking means manually operable only from the inside of the building and an external locking means manually operable from the outside of the building.