Wind Farms Health and Safety

By Dr Richard Griffiths, PhD, MSc, MEd, Cert Ed, Grad R.S.C, CMIOSH, MIIRSM, AIEMA, FRSH, FRIPH

Reducing dependency on fossil fuels is a key element in tackling climate change and there is now a great deal of support from the UK Government for sustainable energy solutions, wind farms being one of them.

Wind farms can have a number of effects on the environment as well as possible health and safety issues. Since the early 1970s the wind energy industry has experienced 14 worker fatalities worldwide, directly or indirectly during wind farm construction or related accidents.

The scope of each life phase of a wind farm is governed by a number of constraints/criteria including predicted wind resource; proximity to residential dwellings; electricity grid connection; access; sites of special scientific interest; military or aviation activity; and availability of land; as well as a number of environmental issues including:

• Landscape and visual impacts - colour, physical structure.
• Hydrology and hydrogeology, soil erosion.
• Noise/vibration.
• Archaeology and cultural heritage.
• Traffic/transport issues.
• Aviation and telecommunications.
• Social and economic impacts and public access.
• Shadow flicker - when the blades rotate, the shadow flicks on and off.
• Blade or tower glint - when the sun strikes a rotor blade or the tower at a particular orientation. (This is a temporary phenomenon for new turbines only, and disappears when blades have been soiled after a few months.)
• Effects on wildlife - from collisions of birds and bats with turbine blades to loss of habitat for certain species and possible disorientation due to ultrasound emissions from wind farms.
• Ecology and nature conservation issues, biodiversity problems, etc.

Health and Safety

A wind farm consists of two distinct systems:

• The high voltage (HV) infrastructure - HV safety rules apply.
• The wind turbines with their associated low voltage (LV) infrastructure - wind turbine rules apply.

The Wind Turbine Safety Rules (WTSR) specify actions and procedures necessary to protect people working on wind turbines from the dangers inherent in the installed electrical and mechanical equipment.

"To carry out work on equipment in a wind turbine, the WTSR require Approved Written Procedures (AWP's) to be put in place for each work package significant enough to warrant it. An AWP is a procedure which specifies how work on plant and apparatus below 1,000V AC or 1,500V DC, which require safety precautions to be taken, will be carried out safely - it is similar to a method statement and it includes checkpoint signatures as auditable proof that precautions were taken and work was completed. The WTSR's also give guidance on where AWP's are required and where they are not necessary." (British Wind Energy Association)

There are occupational safety risks for employees during manufacturing and construction both onshore and offshore including working at heights (particularly in windy conditions), crane and heavy or rotating machinery operations, high voltage electricity, working in hazardous weather, e.g. sleet or snow conditions, working over water, and driving vehicles.

Wind farms, if constructed on or located near airports, may have an impact on aircraft safety directly through potential collision or alteration of flight paths. They may also affect the operation of aviation radar by causing signal distortion, which may cause loss of signal and erroneous signals on the radar screen. Generally, however, wind farms are unlikely to impact on the safety of commercial and domestic air transport as pilots regularly navigate hazards such as power and phone lines.

Similarly, if located near ports, harbours, or known shipping lanes, an offshore wind turbine may have an impact on shipping safety through collision or alteration of vessel traffic.

Construction activities for wind energy projects typically include clearing for site preparation and access routes; excavation, foundation blasting, and filling; transportation of supply materials and fuels; building foundations involving excavations and mixing/placement of concrete; operating cranes for unloading and installation of equipment; and commissioning new equipment.

Decommissioning activities may include removal of project infrastructure and site rehabilitation and tower collapses - all activities producing their associated noise. While most of these are extremely unusual events, these potential occurrences can be mitigated by establishing reasonable setbacks from residences and public corridors based on the size of the turbine and blades.

A turbine blade can break, resulting in blade throw due to improper design, improper manufacturing, improper installation, wind gusts that exceed the maximum design load of the turbine structure, impact with cranes or towers, or lightning. The distance a blade piece can be thrown from a turbine depends on its mass, shape, speed at the time it breaks from the machine, the orientation of the blade at the time of the throw, and the wind speed at the time. These occurrences are rare, due to better testing, design and engineering of commercial wind turbines.

Fire

The risk of fire at wind farms is low, as the flammable components are located high above the ground and there is normally no vegetation around the base of the turbine towers. Similarly, high-voltage connections are underground, and access tracks act as firebreaks and provide fire-fighting access. Lightning protection devices are installed on every wind turbine, while dedicated monitoring and control systems shut down the turbines when the threshold temperatures of critical components are reached.

Wind turbines are often struck by lightning, but are equipped with lightning protection systems, while turbine blades usually have internal lightning conductor rods running all the way to the blade tips.

Typically, a turbine fire is allowed to burn itself out, while protecting against the potential for ground fires that might start due to sparks or falling material. An effective method for extinguishing a turbine fire from the ground does not yet exist and the fires do not last long enough to warrant aerial attempts to extinguish them.

Tower collapses are rare and the reasons for collapses vary depending on conditions and tower type, but include blade strikes, rotor over speed, cyclonic winds, and poor or improper maintenance.

Ice Shedding

Blade icing can occur in severely cold weather when the rotor is stationary. Once operation recommences, blade flexing causes the ice to break off and fall vertically to the ground. Actual 'sling shooting' of ice has not been reported. Turbines will shut down in icing conditions because the wind vane and/or anemometer sensors become frozen, making the turbine inoperable. As the ice melts, it will fall to the ground in the vicinity of the turbine. During operable wind speeds and when the turbine has not yet been shut down automatically or manually, ice can break off the blades and be thrown from the turbine (instead of dropping straight down).

The distance travelled by a piece of ice depends on the position of the blade when the ice breaks off, the location of the ice on the blade when it breaks off, the rotational rate of the blade when the ice breaks from the blade, the mass of the ice, the shape of the ice (e.g. spherical, flat, smooth), and the prevailing wind speed. Design features such as the use of black blades and the application of special coatings have been used. In addition to accumulating on the blades, icing also affects the wind speed and direction sensors on the nacelle that provide information to the control system of the turbine. If the sensors become iced up, turbine operation then stops automatically. When ice melts from the sensor, the control computer automatically returns the turbine to operation. Icing on the blades also results in reduced performance, unusual loads, or vibrations that are detected by the control system and trigger an automatic stop. In these cases, the turbine remains off-line until an operator inspects and manually restarts the turbine. If the turbine is not operating, ice from the blades, nacelle and tower falls to the ground in the immediate vicinity of the machine.

Project operators can halt operation of certain turbines during icing events to prevent ice throws and equipment damage. Provided some wind is available, site operators can manually 'bump' the rotor for a few slow rotations to make the blades flex and relieve some of the ice build-up. Under these conditions, the slow rotor speed will again result in ice falling to the ground in the immediate vicinity of the machine.

Many concerns associated with safety, fire, noise, vandalism, trespassing, icing, blade throw, etc. can be addressed by placing distance (safety setbacks) between the wind turbines and people, property lines, roads, and scenic areas. The most common way to define a setback distance is in terms of a multiple of the turbine height or to specify a fixed distance, or a combination of a fixed distance and a multiple of the turbine height. Establishing adequate setback areas from inhabited buildings, roads and power lines also reduces the risk of injury or damage in the event of ice throws.

Another factor to consider when assessing the risk of ice throws from wind turbines is that the power grid turbine operations stop immediately when grid power is lost, thereby reducing ice throw risks. The people most at risk from falling ice are the site personnel, as most ice falls from the blades, nacelle and rotor near the base of the tower. Most developers have strict rules established for personnel and operations during icing events to prevent worker injury and to protect the public.

Wind turbines and wind power projects are inspected at each phase of design, construction and operation to confirm compliance with these standards and to be certified by an accredited body, e.g. Germanischer Lloyd and Det Norske Veritas.

Other safety/health problems that may arise are due to slips, trips and falls on access ladders due to marine growth (offshore) and platform S02 production inside structures caused by microbes which can also accelerate corrosion.

Noise

Wind plants are quiet compared to other types of industrial facilities, but most industrial plants are not located in rural or low-density residential areas. Wind turbines most commonly produce some broadband noise as their revolving rotor blades encounter turbulence in the passing air, typically a 'swishing' or 'whooshing' sound. Some wind turbines (usually older ones) can also produce tonal sounds (a 'hum' or 'whine' at a steady pitch). This can be caused by mechanical components, or by unusual wind currents interacting with turbine parts. This problem has been almost eliminated in modern turbine design. However, problems can occur in hilly terrain where nearby residences are in dips or hollows downwind that are sheltered from the wind - in such a case, turbine noise may carry further than on flat terrain. There are, though, strict guidelines on wind turbines and noise emissions to ensure the protection of residential amenity.

Most rotors are upwind. (A wind turbine can be either 'upwind', i.e. where the rotor faces into the wind; or 'downwind', i.e. where the rotor faces away from the wind.) A downwind design offers some engineering advantages, but when a rotor blade passes the 'wind shadow' of the tower as the rotor revolves, it tends to produce an 'impulsive' or thumping sound that can be annoying. Today, almost all of the commercial wind machines on the market are upwind designs, and the few that are downwind have incorporated design features aimed at reducing impulsive noise (for example, positioning the rotor so that it is further away from the tower).

Towers and nacelles are streamlined. Streamlining reduces any noise that is created by the wind passing the turbine. Turbines also incorporate design features to reduce vibration and any associated noise, e.g. soundproofing, and mounting equipment on sound-dampening buffer pads. The generator, gears and other moving parts located in the turbine nacelle produce mechanical noise. Wind turbines use special gearboxes, in which the gear wheels are designed to flex slightly and reduce mechanical noise. Wind turbine blades have become more efficient. The more efficient they are, the more the wind's energy is converted into rotational energy and the less aerodynamic noise is created. Small wind turbines tend to be noisier for their size than large machines, due to higher rotational speed of the blade tips, and more research money has been invested in reducing noise from large turbines.

Safety Features

Wind turbines have special inbuilt safety equipment to deal with emergencies, e.g. vibration sensors to detect rotor problems and complete shutdown during excessive wind speeds. Many of the potential risks are reduced by the use of enclosed tubular steel towers (rather than open lattice towers), locking systems on doors, intruder alarms, and protective safety fencing around open switchyards. The only potentially toxic or hazardous materials involved in the operation of wind farms are relatively small amounts of lubricating oils, hydraulic and insulating fluids.

Note: The article above is presented not to give a biased or distorted view of wind farms but as an attempt to identify key environmental and health and safety issues which have presented problems in the past, are doing so at present, or could do so in the future, in order that a continual improvement in these areas is maintained or even bettered.

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