Abstract: The panel assembly has a panel generally fitting in a hole and having an outer periphery running generally parallel to the inner periphery of the hole. Respective geometrically similar inner and outer annular frames on the inner and outer peripheries have confronting outer faces forming an annular gap around the panel between the inner and outer frames. One of the frames has an inner face forming an annular compartment extending around the respective periphery. This one frame is formed with an array of throughgoing openings extending between the respective inner and outer faces and the compartment is substantially closed except at the openings. An annular body of heat-swellable material is provided in the compartment so that on heating of the material it swells and exits the compartments through the openings to fill the gap.

Abstract: An inner frame for a cover and an outer frame for an inspection opening can be formed with frame members having flanges projecting from the plane of the frame and formed with tongues at their ends engageable by resilient hooks of the respective corner elements which fit without play against the frame members. The frame ends are cut at right angles to the longitudinal edges of the frame member in the case of the outer frame and are provided with abutting miters in the case of the inner frame.