Hand Signals and a Load That Will Not Seat
An operator is lowering a 3,000 lb precast panel onto dowels on a wall. The panel is 8 ft tall and the operator cannot see the dowels; a signal person stands at the wall edge with a clear view of both the panel and the operator. The panel hangs about 2 in. high and will not drop onto the dowels. The signal person gives a "lower slowly" signal, then, when it does not seat, gives "raise" and "lower" in quick succession to "bump" it down. The operator, frustrated, raises the panel 3 ft and lets it drop. The panel lands off the dowels and cracks. The signal person had earlier given a "stop" that the operator did not see because he was watching the load.
1. Identify the signal and communication failures in this sequence and the correct procedure for seating the panel.
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Several failures compound. First, a stop signal was given and missed; the operator must maintain attention to the signal person and stop immediately on any stop signal, and the signal person should have used a radio or repeated the stop until acknowledged. Second, "raise" and "lower" in quick succession is not a recognized way to bump a load; the operator cannot reliably interpret rapid reversals, and the crane's controls and brakes do not respond precisely enough for a 2 in. bump. Third, raising 3 ft and dropping the load is a shock-loading practice that can double the effective load on the sling and crane and is prohibited. The correct method: stop, confirm the panel's position relative to the dowels with a spotter at the wall, use a tag line to guide alignment, lower in small controlled increments with a clear "lower slowly" signal and a pause between moves, and use a drift pin or guide to align the panel before setting it down. If the panel will not seat, raise it clear, inspect the dowels and panel for damage, and re-rig rather than forcing it.
2. What should the signal person and operator agree on before the lift, and what does the standard say about who may give signals?
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Before the lift, the signal person and operator should agree on the specific signals to be used, the communication method (hand signals, radio, or both), and a fallback if the view is blocked. They should confirm that the signal person is qualified and that only one person gives signals at a time, except that anyone may give a stop signal. The operator must obey a stop signal from anyone and must not move the load until the signal is clear. They should also agree on a test lift: raise the panel a few inches, confirm the rigging and the panel's balance, and pause before continuing. The signal person should position where the operator can see them at all times, and if the view is lost, the operator stops. For a blind lower like this one, a second spotter at the dowels relaying to the signal person is appropriate, with radios and a confirmed channel check.