An access opening closure assembly consists of a frame structure and a cover panel. The frame structure and cover panel include aluminum profiles. The profile of the frame structure is reinforced by an underlying support section made of steel and, at the corners, by overlying steel angled corners. The profile of the cover panel is reinforced accordingly by underlying bands of sheet steel and overlying steel angled corners positioned at the corners. Therefore, in case of fire, a steel skeleton remains intact for the frame structure as well as for the cover panel, even if the aluminum profiles are melted. Such an access opening closure assembly is characterized by improved fire retarding properties or a higher fire resistance.