An operation mechanism adapted for activating a deceleration device for decelerating an opening movement of a door. The operation mechanism features a first mode of operation and an second operation mode. In the first mode of operation the operation mechanism allows free rotation of the door, when the operation mechanism is loaded by an impulse of the door below a predetermined threshold value. In the second mode of operation when the operation mechanism is loaded by an impulse of the door above the predetermined threshold value the operation mechanism decelerates free rotation of the door by connecting the door to the deceleration device which will then decelerate the acceleration of the door.