Climbing device is the equipment that is used to prevent a fall by a worker from a drilling-rig mast or derrick. A climbing device moves up and down a steel cable that is attached to the top and bottom of the derrick and runs next to the ladder. A worker is attached to the climbing device by a tail rope and safety harness.
The climbing device moves freely up and down the cable unless the worker falls, at which time the device catches the cable to stop the fall. A counterbalanced climbing device has a weight on it equal to the weight of a worker.