Blind Lift with Conflicting Signals
You are operating a 90 t crawler crane setting 6 m x 2.5 m precast wall panels onto the second floor slab of a building under construction. The designated signalperson is at ground level with a two-way radio. At the last 3 m of travel, the panel passes behind a masonry wall, so neither you nor the signalperson can see the load or the landing point. A second rigger stands on the slab at the landing point. The radio channel is shared with the site's concrete pumps and twice you have heard fragments of other conversations through the speaker. On the second panel, the rigger on the slab begins giving hand signals that contradict the radio instruction. Shortly after, the radio goes silent for 20 seconds while the panel is suspended at 12 m radius and about 8 m off the ground. Wind is 8 m/s, gusting 11 m/s, and each panel presents roughly 6 m2 of sail area.
1. Who is permitted to direct the lift, and what do you do when the signals conflict or the meaning is unclear?
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Only the designated signalperson directs the lift. That designation is made in the lift plan, and the signalperson must be competent, have been briefed on this lift, and be identifiable - high-visibility vest, agreed radio channel, and a clear understanding of who is in charge of the load.
The exception is universal and applies to everyone on site: any person may give a stop signal, and the operator must obey it immediately. That is not a transfer of control; it is an emergency intervention.
The rigger on the slab is not the designated signalperson here. Two sources of instruction is worse than none. The correct response when hand signals contradict the radio is to stop, hold the load steady and clarify before moving a lever. If the blind section genuinely requires a second person to direct the landing, that must be planned before the lift: the signalperson hands over to the slab rigger at an agreed point, in an agreed sequence, with the operator acknowledging the handover and only one person directing at a time. Ad hoc, mid-lift handover is how loads get pulled into walls and people.
If you cannot tell what a signal means, do not interpret it. Stop and get it repeated or resolved.
2. The radio goes silent with the panel in the air. What do you do, step by step?
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- Stop. Hold the panel stationary with the controls neutralised, keeping it clear of the wall, the slab edge and personnel. Do not boom down, slew or hoist on an assumption about what is happening out of sight.
- Try to re-establish contact on the agreed channel and, if the crane has a public address or horn, use the pre-arranged signal to attract attention.
- Look for a person you can see. If the slab rigger steps into your view and is the pre-designated relay, take hand signals from that person only, and only for the movements needed to land the panel at the planned position. Hand signals must be the standard ones, given deliberately and repeated if you are unsure.
- If contact cannot be re-established, follow the emergency procedure in the lift plan: keep the load over a clear area, keep the area below barricaded, and lower it to a pre-briefed safe landing position where it can be set down and secured, with a spotter in your view who can give a stop signal. A load must not be left suspended and unattended, and it must not be landed on a spot that has not been cleared.
- Do not continue the lift. Once the panel is safe, the job stops until communication is restored and the cause of the silence is understood - a dead battery mid-lift is a planning failure, not bad luck. Spare batteries and a backup channel belong in the plan.
3. What planning and controls should have prevented this situation, including the wind and the panel's sail area?
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The lift plan should have identified the masonry wall as a blind section on a dimensioned drawing, not discovered at 3 m from the landing. From that, the plan would set out a relay or handover signalperson, positions where each person can see the load and be seen by the operator, and a single agreed radio channel - ideally a dedicated one, since sharing with the concrete pumps allows cut-in and missed calls. A pre-lift meeting with the operator, signalperson, riggers and supervisor would confirm names, channel, handover point, stop signals and barricades. Radio checks before each panel, and spare batteries, are basic.
The wind needs specific treatment. 8 m/s gusting to 11 m/s with 6 m2 of sail area is a significant side load on a panel standing on edge. Check the manufacturer's load chart and notes for the permissible wind speed and the permissible load sail area for the configuration - many charts limit allowable pressure per unit of load area, and the boom length and radius change that limit. Gusts are what matter, not the average. Tag lines with people outside the fall zone keep the panel from rotating and building a pendulum, and they must never be used to drag the load against the wind. If the measured gust exceeds the chart limit, or control of the panel becomes uncertain, the lift is postponed.