An interlock vessel having an air-tight body with opposing ends. A portion of the body is designed to fit into a decompression (hyperbaric) chamber, wherein a diver or a patient undergoing a decompression treatment is positioned. The opposing ends are closed by pivotally moveable doors and locking assemblies that retain the doors in a closed position until the pressure inside the decompression chamber and the exterior of the chamber can be equalized. The outer door has two locking systems: (a) an interlock system and (b) a safety/delay locking system. Both locking assemblies are manually operated.