Conflicting Signals on a Blind Roof Lift
An operator is setting a 4,200 kg air-handling unit on a roof 18 m above grade. The operator cannot see the load or the landing area from the cab. Signalperson A is on the roof with a radio on channel 7. Signalperson B is on the ground to watch the load for power-line clearance, but B's radio battery dies. A gives a hand signal to hoist. At the same moment, the operator sees B give a stop signal with an arm extended, palm down, because a worker has walked under the suspended load. The operator stops. A then radios, “Keep going-B is not a signalperson, I am in charge.” The load is still 2 m above the roof and drifting slightly in the wind.
1. Who has authority to direct the lift, and must the operator resume on A's instruction? Explain.
Read the worked answer
A is the designated signalperson, but B has authority to give an emergency stop. The operator must stop and remain stopped until the reason for B's stop is cleared-here, a worker under the load. A cannot override an emergency stop by radio. The operator should acknowledge the stop, keep the load suspended and controlled if safe, and not resume until the area is clear and A gives a clear, understood signal. If the load is drifting or the suspension is unsafe, lower it to a safe landing.
2. What communication failures contributed to the situation, and what controls should be in place before restarting?
Read the worked answer
Failures: shared radio channel, no radio check, no backup signal, B not included in the lift plan, no exclusion zone under the load, and two people giving signals. Before restarting: use a dedicated channel and confirm it; perform a radio check; agree on hand signals as backup; designate one signalperson with stop authority for any worker; barricade the landing zone; hold a pre-lift briefing; and confirm the operator's blind spots and relay method. If communication is lost, stop.
3. Describe the steps you would take from the stop to the next safe movement.
Read the worked answer
Stop, hold, and assess. Clear the worker from under the load, lower the load to a safe height or ground if wind drift is a concern. Confirm radio contact on the dedicated channel, confirm A is the only signalperson, and confirm B's stop is resolved. Rebrief the crew, check the load and rigging, then resume with slow, controlled motions. Keep tag lines on, maintain the exclusion zone, and stop immediately if signals are unclear or lost.