Wind, Night, and a Sidewalk Under the Swing
Night concrete pour. A 50-ton crane is flying a 20 ft x 8 ft solid form panel - roughly 160 sq ft of sail - onto a third deck. In the last 20 minutes wind has gone from 12 mph to 24, gusting 31. The panel manufacturer rates it for 20 mph. One of the two tower lights is failing and the set point is now in shadow. The panel is 8 ft off the deck and starting to sail. The crane's swing path carries the load over a public sidewalk that is still open. The superintendent keys the radio: 'Get it set, we're on the clock.' You are the only signalperson on the job.
1. Who stops this lift, and how do you handle the superintendent?
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You stop it. Stopping an unsafe lift is part of the signalperson's job, not an overreach. Give STOP (or ALL STOP on the radio), then land the panel at a planned safe location rather than holding it in the air indefinitely.
State the conditions, not an opinion:
- Panel rated to 20 mph; actual 24, gusting 31.
- Set point in failing light - you cannot judge position or alignment, and the operator cannot see you judge it.
- The swing path crosses an open public sidewalk.
On the superintendent: production pressure is not a hazard control, and no one on the site - superintendent included - can direct an operator to override a stop. Make the conversation about what has to change to resume: sustained wind below the panel rating, lighting restored at the set point, sidewalk closed or the pick re-planned so the load never crosses it. That turns an argument into a decision.
Do not compromise in the middle - 'just this one panel' is the exact moment the gust arrives.
2. The superintendent says the panel only weighs a few thousand pounds, well under the chart. Explain why wind is the controlling factor, not weight.
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The load chart describes a static load in still air, with the crane level and the load directly below the tip. Wind is a force the chart does not show.
Why it dominates here:
- Wind force scales with sail area and with the square of velocity - a 31 mph gust loads the panel roughly seven times harder than 12 mph did, on the same 160 sq ft.
- The panel manufacturer's 20 mph rating is a hard limit on the panel and its lift fixtures. Exceeding it risks the form failing or the inserts pulling out - a failure the crane's capacity has nothing to say about.
- The gust pushes the load outward, which increases radius and lowers capacity at the same moment the boom is taking a side load from the swinging panel.
- In failing light, neither you nor the operator can see the load's attitude early enough to correct it.
Conclusion: 'It's under chart' answers a different question than the one being asked. The lift is limited by wind, visibility, and the public way beneath it - none of which appear on the load chart, and none of which improve by swinging slower.
3. The swing path crosses an open public sidewalk. What is your responsibility before the panel moves again?
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No signalperson should direct a load over people, and a public sidewalk is not a controlled area - you cannot rely on pedestrians to notice a crane at night.
Before the next movement:
- Close and barricade the sidewalk, or re-plan the pick so the entire swing path stays inside the fence. If it is a public way, that closure is a site-management action, not something the signalperson improvises.
- Confirm the exclusion zone matches the actual swing radius, including the extra radius the load picks up when it swings wide.
- Brief the operator on the revised path and the new stop points.
- If the closure cannot be arranged tonight, the pick waits. There is no version of this where the load is hurried past a pedestrian.
If someone walks in mid-swing: stop, hold, wait. Never try to time it. The signalperson's stop is the fastest available control, and the load comes to rest where it is safe to land it - not where it was originally headed.