Cranes are powerful and efficient machines used in various industries to lift heavy objects, but when strong winds come into play, proper safety measures must be taken. Wind speed is a critical factor in safe crane operation and must always be considered. This post will go through the essentials of safe crane operation during windy conditions.
When working in wind, it's important to consider the following factors in order of importance:
1. The Load Every load has its own characteristics that need to be taken into account when working in wind. Wind resistance is a major factor that affects the stability of the load and the crane, along with wind speed and direction. This may cause the load to move uncontrollably or the crane to exceed known limits. To minimize risks, consider the cross-section of the load exposed to the wind relative to the load's weight. Use tag lines where possible while following the manufacturer's wind speed guidance.
2. Manufacturers Limit Every make and model of crane has its own limits set by the manufacturer based on the crane and its configuration. There may be limits for setup and operation specified by the manufacturer. These limits should never be exceeded.
Typical maximum in-service wind speeds are:
- Tower cranes 20 m/s (45 mph / 72 kph)
- Crawler cranes 14 m/s (31 mph / 50 kph)
- Mobile cranes 9.8 m/s (22 mph / 35 kph)
For specific limitations on the crane in use, check with the manufacturer. Operational limitations may well be lower than these figures, e.g., when handling loads with a large wind area such as wide formwork panels.
3. Crane Operators Limit The crane operator is the most experienced person on the crane, and their experience and knowledge of the load and manufacturer's specification is vital. The crane operator is also the best person to take into account the wind direction and boom configuration. Wind forces acting on the rear of the boom can result in decreased forward stability, wind forces acting on the underside of the boom can result in decreased backward stability, and winds acting on the side of the boom can result in structural damage.
4. The Crane Companies Limit The controller of the crane may impose limits under their responsibilities for the crane as stated in the Pressure Equipment, Cranes and Passenger Ropeway Regulations. The controller is often the most experienced and knows the crane operator's competency and the equipment's capability. Our experience is that crane companies often set a figure of 9.8 m/s as a point that the wind must be considered for safety. This may be lower or higher based on points 1 - 3 above.
5. The Site Limit Every site is different, and the owner of the site is often the most experienced person in local conditions and may set a limit on activities based on the site. The wind speed should take into account the speed the wind is gusting in the area of operation, its frequency, and duration.
When working with cranes and wind, it's also important to take into account wind forces acting on the load. This Wind force can be calculated based on formulas outlined in a guideline issued by the Federation for European Manufacturers - product group cranes and lifting equipment. This formula is reasonably complicated, so it's best to contact the Crane Association of New Zealand or us for further information on its use.
To read more on Wind Safety for cranes, we recommend reading a document produced by Liebherr called "Influence of wind on crane operation".