Blind Lift with Lost Radio Communication
A 3,000 lb die half must be set on a press bed that the cab operator cannot see because of a wall. A designated signal person on the floor is using a two-way radio and has been briefed on the travel path. The load is 6 in above the press bed when the radio goes dead. The signal person is now out of the operator's line of sight; a fogged mirror that might show the floor is mounted near the cab. A second worker, trained as a signal person but not assigned to this lift, is visible to the operator. The press bed is clear and no one is under the load.
1. What should the operator do the moment communication is lost?
Read the worked answer
Stop all motion and hold the load.
Reasoning: the operator has lost the only reliable information about the load's position relative to the press bed. Continuing to lower 'a little' is a blind move; 6 in of travel is enough to crush a hand, jam the die, or shock-load the rigging on the bed. The controlling rule is that a crane must not be moved when the operator cannot see the load or the signal person and has no communication.
The operator should not:
- lower the load on the assumption that the bed is clear,
- act on the fogged mirror,
- accept signals from the unassigned worker without confirming that person is authorized and in a safe position.
Holding position is safe here because the load is only 6 in above a clear bed and the area under it is empty. If the load were over people or a fragile area, the operator would still stop and hold and call for help.
2. How should communication be re-established, and who may give which signals?
Read the worked answer
Re-establish communication in this order:
- Get a signal person into the operator's view. The assigned signal person should step to a position the operator can see and use standard hand signals; the operator should confirm visually.
- If that is not possible, use the trained second worker as a relay, but only after the operator confirms with the assigned signal person (or supervisor) that the relay is authorized. A relay must pass the exact signal, not interpret it.
- Restore the radio with a spare battery or another unit, and do a radio check before any motion resumes.
Signal authority:
- Hoist, lower, travel, and stop signals come from the designated signal person.
- Emergency stop may be given by anyone on the site; the operator must obey it immediately.
- The operator must not act on hand signals from an unidentified person, and must not move on a signal that is unclear or ambiguous.
3. What signals and sequence should be used to finish the set?
Read the worked answer
Before motion, the operator and signal person should agree on the sequence and confirm the load is still over the clear bed.
Sequence:
- Lower signal (arm extended down, palm down, move hand down) in short increments until the die is just above the bed.
- Stop (arm extended, palm down, move arm back and forth horizontally) and check alignment.
- Lower slowly to set the load; then hoist slightly to confirm the rigging is slack and the load is stable.
- Dog everything (hands clasped in front of the body) to hold all motions while the rigging is disconnected.
At any point, an emergency stop (both arms extended horizontally, palms down, moved back and forth) from anyone overrides the sequence. After the set, the operator should not travel until the signal person confirms the rigging is clear and gives the travel signal.