The 19 t Pick That Grew a Tail
You are operating a 20 t capacity slewing mobile crane on a level concrete hardstand at a precast yard. The load chart for your current configuration (main boom, no jib, outriggers fully extended, 360° slew) allows 4.2 t at a 14 m radius. The rigger tells you the precast panel weighs 3.6 t and gives you a tag line. You lift, and at about 13 m radius the crane's rated capacity indicator (RCI) alarm sounds and the boom starts to deflect more than you expect. You stop the lift. The panel is still 1.2 m off the ground. The rigger says the panel is 'about 3.6, maybe a bit more, it's wet'. Your supervisor is not on site and is not answering the phone.
1. What is the immediate safe course of action, and what does the RCI alarm actually tell you?
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The RCI alarm is not a suggestion - it is telling you that the actual load moment at the boom has reached the rated capacity for the current radius and configuration. Stop, hold the load steady, and lower it to the ground under control if it is safe to do so; do not slew, boom out, or try to 'beat' the alarm by booming up. The fact that capacity is 4.2 t at 14 m radius but the alarm is sounding at about 13 m means the real load is heavier than 3.6 t, or the radius is being measured to a point further out than the rigger thinks, or both. Radius is measured from the slewing centre to the centre of gravity of the load, not to the hook or the edge of the panel. A long panel whose centre of gravity sits further out than the hook block adds effective radius. Treat the lift as failed until you have facts.
2. The supervisor is uncontactable. What must happen before the lift resumes, and who is responsible for what?
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The lift does not resume on a guess. The panel must be weighed or its mass confirmed from a documented source (delivery docket, manufacturer's mark, or a certified weighbridge ticket), and the rigging geometry re-checked so the true radius to the load's centre of gravity is known. The crane operator is responsible for refusing to lift beyond the chart and for not accepting an unverified mass; the rigger is responsible for accurate slinging and for reporting the true mass and any change; the person controlling the lift (supervisor or appointed dogman) is responsible for authorising the lift plan. If the supervisor cannot be reached, escalate to the next competent person - the site manager or the crane owner's appointed person. A wet panel does not gain 0.6 t from water alone; that excuse should be treated as a signal that the mass was never known, not as an explanation.
3. Assume the panel is confirmed at 4.0 t. Can you complete the lift, and what would you check first?
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4.0 t at 14 m against a 4.2 t rating is only 95% of capacity - technically inside the chart, but a poor margin for a precast panel with wind area and a wet surface. Check: (1) the exact radius at the worst point of the slew path, not just the pick point; (2) ground bearing under the outrigger pads, since deflection suggests loading is higher than assumed; (3) whether the chart you are using is for the correct outrigger configuration and slew zone; (4) wind speed and the panel's sail area; (5) whether a tag line and controlled descent are in place. If any of these is uncertain, reconfigure - reduce radius by repositioning the crane, or add counterweight if the chart permits - rather than operating at the edge of the chart. The right answer is rarely 'it fits, so lift it'.