Wind and weather at crane lifting

Weather can make an otherwise well-planned lift dangerous. Wind, poor visibility, cold and ice affect both the crane, the load and the person working. Therefore, an assessment of weather conditions is a fixed part of planning when lifting outdoors.

The wind grabs at the load and the crane's boom and can set the load in motion so it begins to swing or rotate. With high lifts and long booms the crane becomes more sensitive to wind forces. A load that suddenly catches the wind can become difficult or impossible to control and it can in the worst case affect the crane's stability.

The executive order on the use of technical equipment is clear: Outdoor use of cranes must be stopped immediately if the weather becomes so bad that it affects safety and exposes people to danger (BEK no. 428 of 05/04/2022 § 57). How much wind is allowed is stated in the crane manufacturer's instructions. That is the limit that applies to your crane. Even a light wind can make the load swing, so you may have to stop earlier (BFA Bygge & Anlæg).

It is not only the wind's strength that determines the danger, but also the shape of the load. A large, flat load — such as a plate, an element or a light, voluminous object — catches much more wind than a compact, heavy load with a small surface. Two loads of the same weight can therefore behave very differently in the wind.

BFA Industri gives a simple rule: The wind force doubles when the surface of the load doubles — and becomes four times as large when the wind speed doubles.

BFA Industri writes about outdoor overhead and gantry cranes that, as a rule of thumb, crane work is stopped at wind force 7 (13.9-17.1 m/s) on the Beaufort scale — and earlier if the load has a large surface. The manufacturer's limit for your crane always applies first.

Pendulation and rotation can be dampened with a guide line so you can hold the load at rest from the ground without standing under it. But a guide line has its limits: if the wind takes too much hold, the load cannot be safely controlled anymore, and so the lift is postponed until the wind subsides.

BFA Industri recommends a tag line for outdoor crane work. It keeps the load from rotating and prevents the slinger from getting trapped.

Poor visibility — fog, heavy rain, snow, or darkness — makes it difficult for the driver and signaler to see the load and area and communication becomes uncertain. Cold and ice can make the surface slippery, freeze mechanics, and make tools and surfaces slippery to handle. All these factors are included in the assessment of whether the lift is safe.

In winter, the load can be covered with snow or frozen to the ground. That makes it heavier than you think and increases the risk of the crane being overloaded or overturning (BFA Industri).

When weather makes the lift uncertain, it's postponed. That's a professional decision, not a defeat: a lift can always be done later when conditions are better. Doubt about wind counts the same as doubt about weight or stability—if there's doubt, there's no lift.