Abstract: The invention provides a flap valve for controlling the air pressure within a protected space defined by walls, the flap valve including a valve frame attachable to an opening made in the walls, a valve flap, articulated at least indirectly to the frame and being subjectable to both a sealing force which forces the valve flap against the valve frame and to an opening force which lifts a portion of the flap off the valve frame; the flap valve having a first position in which the protected space is sealed off from a contaminated environment, and a second position in which air from the protected space is allowed to escape into the environment via the opening, wherein the sealing force is constituted by at least one spring at least indirectly attached to the valve flap and the valve frame.

Abstract: The invention provides a sealable lead-through system for a protected space defined by walls, the system including at least one sleeve made of a flexible material, one end of the sleeve being tightly attached to the outside of one of the walls, at least one sealing element, approximately fitting the sleeve and being made of a material deformable in compression, the sealing element being provided with a bore approximately fitting the size of a transfer member intended to be led from outside the protected space into its interior or vice-versa, the sealing element being adapted to be subjected to a compressive force, for sealing off any interspaces between the transfer member and the bore, and between the sealing element and the sleeve.