A closure [10] for a cylindrical vessel includes at least one holding means [30] configured to move the closure into a fully closed state, the holding means having a predetermined actuation force or torque to properly close the closure, the closure including one or both of the following failsafe failure detection features: a mechanical fuse [20] having a predetermined load failure force below that of a load failure force of at least one component of the holding means and above that of a predetermined actuation force or torque to properly close the closure; or a block[40] sized to at least partially overlap a pressure warning lock hole [19] of the closure door when the closure is not in the fully closed state and to fully expose the pressure warning lock hole when the closure is in the fully closed state, thereby permitting insertion of a pressure warning lock [17].