AIRCRAFT INCLUDING A FLOOR AND A FIREPROOF AND/OR SMOKE-TIGHT HATCH

An aircraft having a structure, a fuselage, a floor separating the fuselage in two, wherein the floor has openings, and, for each opening, a shut-off system having a flap hinged on the structure between a standby position in which the flap does not shut off the opening and a protective position in which the flap shuts off the opening, a return arrangement that urges the flap into the protective position and a retaining element that keeps the flap in the standby position and breaks when its temperature exceeds its melting point. Thus, when a high-temperature gas flow reaches the retaining element and this high temperature is higher than the melting point of the retaining element, the latter breaks and releases the flap, which shuts off the opening.