Boom Up, Wind Rising
You are lifting a 1.2 t, 6 m × 3 m signage panel onto a building facade. The crane is set up on the street side, outriggers fully extended, boom at 45°, radius 12 m; the chart allows 3.5 t there. The panel has a large sail area and the wind is gusting. The forecast said 15 km/h, but the flags are standing out and a handheld anemometer reads 28 km/h gusting to 38 km/h at ground level. The panel is 8 m up and the dogman wants to 'get it done before it gets worse'. A pedestrian barrier is 4 m from the outrigger pads, and a bus route runs past the site.
1. What is the wind limit for this lift, and what should you do?
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The manufacturer's load chart and operating manual give the maximum permissible wind speed for the crane and for the load's sail area - you must check the manual, because the limit depends on the panel's area, not just the crane. As a rule, a large sail-area panel is the limiting factor, and many charts stop at around 20 km/h (about 11 mph) for such loads, or specify a reduced capacity above a threshold. Ground-level readings understate wind at height, and gusts are what matter. At 28 gusting 38 km/h, with a 6 × 3 m panel, you are very likely outside the permissible limit. The correct action is to stop the lift: lower the panel to the ground, secure it, and do not resume until the wind is within the chart's limit and steady. 'Get it done before it gets worse' is exactly the reasoning that causes incidents - the gust that catches the panel is the one you cannot predict.
2. How does the panel's sail area change the crane's behaviour even below the wind limit?
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Wind on a 18 m² panel acts like a side load on the boom and a horizontal force on the load. It increases the effective radius as the panel is blown away from the crane, and it adds a moment the load chart does not account for - charts assume still air. It also makes the panel behave like a sail: it will weathervane, swing on the slings, and resist being controlled by a tag line. The result is a load that is harder to land accurately, a boom under side load, and a risk of the panel striking the facade or the building's edge. Tag lines help control rotation but cannot overcome a gust. The practical controls are to keep the load low, minimise the time it is suspended, use two tag lines with people clear of the drop zone, and stop if the panel starts to weathervane.
3. What site controls apply given the pedestrian barrier and bus route?
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The exclusion zone must cover the full area the load could reach if it swung or fell - not just the 4 m to the barrier. With a 12 m radius and an 8 m height, the drop zone and swing zone extend well past the barrier, so the barrier must be relocated or the crane repositioned so the load path never passes over the public footway or bus route. The bus route may require a road closure or a lift window agreed with the traffic authority, and a spotter at the barrier to stop pedestrians. The outrigger pads must be checked for underground services and for the footway's bearing capacity. If the exclusion zone cannot be made to cover the swing and drop zone, the lift should not proceed at that position - the answer is to re-plan the crane position, not to rely on the barrier.