Abstract: A improved seal for a outwardly opening door in a pressure vessel is achieved by providing an elastic inflatable tube in a groove between opposed facing surfaces rigidly associated with the door and with the vessel chamber. The groove and tube completely surround the opening of the chamber in a closed fashion. Clamps are provided to retain the door on the chamber. After the door is closed, the tube is inflated to a pressure at least equal to the pressure in the chamber and sufficient to cause the tube to fill any gaps caused by distortion of the door under the effect of the outward pressure from the chamber.