The safe operation of the closure is ensured by a redundant design in which the closure cannot be opened without the removal of the pressure alert valve and the movement of the safety lock. The pressure alert valve also provides the operator an indication of the presence of any residual pressure in the vessel should the operator inadvertently attempt to open the closure prior to all pressure on the vessel being relieved. Additionally, the safety lock mechanism prevents the door handle from being moved to the open position until after the pressure alert valve has been safely removed. The safety lock must also be returned to the locked position in order for the pressure alert valve to be installed.