Abstract: Fire door leaf for industrial use in relation to openings in structures such as buildings, vessels and/or land and sea-based oil and gas installations, where the fire door with said fire door leaf contributes to providing a passage between different compartments in said structures. The fire door leaf is constructed to work as an element in a certified barrier against the spreading of fire, smoke and/or pressure. The leaf comprises two leaf elements where each leaf element comprises a main surface, and where the leaf elements assembled is suitable to forming a volume between themselves without stiffening elements within the volume. At least one main surface comprises a single-curved surface.