Abstract: A reverse-buckling rupture disk assembly provides a cylindrical housing having a bore for conveying flow through the housing. Mounted within the housing is a frangible concave-convex disk which is connected along its peripheral edge to the housing so as to form a closure to the bore. The disk is designed to resist pressure on the convex side up to a predetermined pressure and then collapsing after the predetermined pressure is reached. A knife blade is positioned within the housing bore on the concave side of the disk for perforating the disk when it collapses. The ends of the blade are connected to the inner surface of the housing or are connected on one side of the lateral center line of the bore. The knife blade is spaced from the inner surface of the housing at least along a substantial portion of its length. The knife blade can be serrated and is preferably curved. The blade can be generally U-shaped so that both ends of the knife blade are connected to the same half of the housing wall.