Worker Health and Safety on Offshore Wind Farms - Special Report 310 (2013) / Chapter Skim
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2 Hazards of Wind Farms1
2 Hazards of Wind Farms1
Pages 19-43
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of the committee's charge, this chapter briefly describes the hazards involved with the phases of wind farm development and provides background for the more in-depth discussion of offshore hazards in Chapter 4. In addition, Chapter 2 provides an introductory comparison of the relative risk of hazards associated with offshore oil and gas operations that are relevant to offshore wind farms and that will be discussed further in Chapter 4.
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. For offshore wind turbines and land-based wind turbines, once the technician is inside the wind turbine, most tasks are exactly the same.
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The foundation is a structural support system that stabilizes the wind turbine by transferring the vertical and horizontal forces acting on it to the surrounding ground. For land-based turbines, foundations are generally some type of reinforced concrete slab, monopile, or multipile solution and are determined by the geotechnical conditions of the site (AWEA n.d.)
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FIGURE 2-3 Offshore 5-MW wind turbine with wind technicians on board. (Source: http://www.areva.com.)
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. Wind Farms As mentioned in Chapter 1, the National Renewable Energy Laboratory (NREL)
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. Wind farms consist of one or more independently operating wind turbines that generate power, are connected together with electric cables, and are connected to an electrical substation.
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Trucks hauling components and installation equipment must travel over existing roads, often to remote areas, which limits access to areas and ultimately the size and capacity of land-based turbines. In contrast, marine transportation and installation equipment can accommodate larger and heavier turbine components for offshore wind farms.
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Developers of land-based wind farms must consider many issues.4 The preinstallation phase involves identifying a potential wind farm site and understanding the suitability of its wind resources -- important factors for any developer. NREL provides some information on existing wind resources for the United States.5 More detailed wind resource data are collected through meteorological towers installed at or near the potential site, a process that can take up to 3 years but that can provide data useful in optimizing turbine location.
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, how cabling between turbines will be done and the electrical power exported to shore, what port facilities will be needed, the overall operations and maintenance strategy, and the decommissioning plan. The developer is constantly aware that work on the wind farm occurs in a marine environment and that all access to the site is by boat or by helicopter; workers cannot just drive up to the work site and get out of their truck, nor can they easily evacuate a wind turbine in an emergency.
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Installation This phase involves the installation of major components, among them the foundation and transition piece, and the assembly of the wind turbine. It includes most of the heavy lifting of turbine components.
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. Installation of the foundations or substructures for a wind farm will be complete or well under way before that of the wind turbines themselves begins.
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In larger wind farms and those farther offshore, the ESP is sometimes a manned structure providing living quarters for turbine technicians, medical personnel, and personnel watching the wind farm's remote monitoring systems. It is also provided with advanced rescue equipment and has a helicopter landing platform.
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This phase is of particular interest because the risk of electrical incidents is now present.9 Operations and Maintenance Once they are operational, wind farms are essentially unmanned offshore facilities with personnel accessing them only to perform maintenance and repairs. Scheduled maintenance ensures ongoing functionality of the equipment and system, and scheduled inspections evaluate condition; maintain safety systems; and satisfy lease, permit, and regulatory requirements.
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Decommissioning Current regulations require wind farm operators to decommission or remove all facilities and wind farm components at some point in the future.12 The committee is unaware of any offshore wind projects that have been decommissioned anywhere in the world, but the process is understood to be the reverse of the installation process and could be more hazardous and difficult than the installation phase. This process would include the removal of all underwater cables, wind turbines, towers, ESP, transition pieces, and foundations and would require equipment and vessels similar to those used during installation.
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The installation of electric cables between turbines and to a substation and then to the grid is interconnected in a similar pattern in land-based and offshore wind farms, but the introduction of water in the offshore environment adds another dimension, since cable installation is accomplished with remotely controlled vehicles. Likewise, the manual handling of components, for example bolts and cables, in a wind turbine is similar for land-based and offshore facilities, as are most of the tools and equipment.
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Logistical coordination with the transport vessel is critical for successful offshore work. Offshore communication and logistics are also critical as more work teams are shuttled by transfer vessels and work simultaneously in more wind turbines.
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As offshore platforms became larger and moved farther from shore, the transfer of workers by helicopter became more routine. On some European offshore wind farms workers are lowered from a helicopter to a platform on the nacelle, but for the most part offshore wind farm workers will continue to rely on transfers from a boat to the ladder and the transition piece on the wind turbine.
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Although cranes are used on wind turbines, they are used less frequently and involve fewer personnel. Hazards involved in Wind Farm development Hazards to worker health and safety related to wind farm development can occur during the major phases of the project: installation, commissioning, operations and maintenance, and decommissioning.
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Chemical exposure Confined space entry Crane and lifting Demolition (decommissioning only) Diving Dropped objects Electrocution and arc flash Emergency evacuation Electric and magnetic field exposure (operations only, once power is being generated)
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Among them are personnel transfers between vessels and wind turbines; helicopter access to offshore facilities; allisions between vessel and wind turbines; collisions between two or more vessels operating in the same area; falls into water by personnel; diving hazards during foundation installation, cable laying, and regular turbine inspections; evacuation from a wind turbine during a fire, explosion, or severe weather event; and the travel distance to and from shore during emergencies. Hazards of Offshore Oil and gas Facilities relevant to Offshore Wind Farms Many offshore oil and gas hazards and their associated risks are similar to those of offshore wind farms.
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Confined space entry Similar Wind turbines have more confined spaces and must be entered more frequently; regardless, confined space entry for both oil and gas and offshore wind carries inherent risk and can have serious consequences. Falls into water Similar Activities in locations where falls into water are likely are similar.
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The hazards and risks between offshore wind and offshore oil and gas are not always directly comparable. After installation, offshore wind farms are more like oil and gas production platforms and less like oil and gas drilling rigs.
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to access wind turbines, weather conditions and sea state will determine the accessibility of the wind farm. The dependence on a vessel to access offshore wind turbines creates issues not only when the technician transfers back and forth between the vessel and turbine but also when the worker needs to evacuate or requires spare tools or components.
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The oil and gas industry works with a more volatile product, and the risk of an explosion or fire on an offshore oil and gas platform is greater than on an offshore wind turbine. Furthermore, offshore drilling platforms are manned and thus pose a greater risk to human life than does the unmanned wind turbine.
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2011. Special Report 305: Structural Integrity of Offshore Wind Turbines: Oversight of Design, Fabrication, and Installation.
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