Tower cranes are exposed to a vast amount of hazards with one of the main hazards being wind. Between 2000 and 2010, there were 1125 tower crane accidents reported worldwide, resulting in over 780 deaths. One of the main culprits behind these tragedies was exposure to wind, which caused directly 23 percent of all accidents and probably more as a contributor factor of other primary causes.
There are many blogs and guidance documents from HSE on this very subject which are helpful but from our point of view, you MUST measure continuously the wind speed with an anemometer mounted directly to the crane. The wind profile of a construction site is very unpredictable as its surroundings are continuously changing. Forecasts are good as guidance only.
EXTRACT FROM HSE – SAFE USE OF LIFTING EQUIPMENT, LIFTING OPERATIONS AND LIFTING REGULATIONS, APPROVED CODE OF PRACTICE AND GUIDANCE
This guidance is issued by the Health and Safety Executive. Following the guidance is not compulsory, unless specifically stated, and you are free to take other action. But if you do follow the guidance you will normally be doing enough to comply with the law. Health and safety inspectors seek to secure compliance with the law and may refer to this guidance.
Where lifting equipment and/or its load may be affected by high wind, appropriate devices should be made available and used so as to detect dangerous situations and allow measures to be taken to cease using the equipment.
Where appropriate, the maximum wind speed in which the lifting equipment can be used should be included in the instructions on use. Measures therefore should be in place to determine the wind speed and also reduce its effect.
Wind effects can be relevant both indoors and outdoors. Equipment use and selection should take account of this
When planning the installation of lifting equipment that will remain erected in high winds, the planning process should take into account the out-of-service winds that it could be subjected to (requirements for tower cranes are given in BS EN 14439). The foreseeable wind speeds will depend on where the crane is to be installed. A local wind speed study should be carried out by a person competent to do so, to assess the effects of the site location, terrain roughness and any tall structures in the vicinity. It may be necessary to restrict the maximum erected height or increase the size of the foundations and/or ballast.
Provide an accurate indication of the prevailing wind conditions at a particular moment in time for a particular areas supported by some weather forecasting. Monitoring wind gusts and turbulence is also very important.
The most common way of providing an indication of the wind speed is to fix an anemometer (wind speed sensor) to the lifting equipment. It should be fixed in the most exposed position, usually on the top of the lifting equipment.
The shape of the load, and the way it is lifted, could also increase the effects of the wind and consequently may affect the stability and rated capacity of the lifting equipment. The larger the surface area of the load presented to the wind then the greater the effect a gust of wind will have on the load and consequently to the strength and stability of the lifting equipment, as well as on the safety of nearby workers. This should also be taken into account when selecting lifting equipment for use. The crane manufacturer will be able to supply information on the maximum permissible in-service wind speeds and any derating for items with a large surface area.
To reduce wind effects on the lifting equipment and/or the load it may be necessary to set ‘wind action levels’, ie the wind speed(s) that require additional measures to be taken to ensure that the lifting equipment remains stable. The manufacturer will be able to provide this information.
The measures will vary depending upon the lifting equipment but could include ceasing to use it until the wind dies down (winding off), lowering the load to the ground, or dismantling the lifting equipment but ensuring it is left in a safe condition. This could apply to suspended access systems or to rope access work.