Fire that has started in an enclosed space in an aircraft is smothered by closing or at least partly closing any air flow inlet and any air flow outlet of the enclosed space in response to a temperature rise caused by a fire in the enclosed space such as a toilet or crew quarters, galley cabinets, or the like. For this purpose fireproof, intumescent material is installed next to and along any apertures or openings in the enclosed space. When the temperature in the enclosed space exceeds the expansion temperature of the fireproof intumescent material the material expands into these apertures, thereby sealing or at least partly sealing these apertures, whereby air and thus oxygen access to the fire is reduced or even prevented, thereby smothering the fire. Preferably a guide surface guides the expanding intumescent material into the apertures or openings at least when the expansion starts.