BY GEORGE H. POTTER
As fossil fuels become more scarce AND harder to locate and exploit, researchers have explored alternative energy sources such as solar, biofuels, wind, and ocean waves, with more or less positive results, as some of the viable solutions. Of these solutions, wind (aeolic energy) is proving to be a substantially clean and efficient alternative energy source although quite costly because of engineering, fabrication, and exploitation expenditures.
WIND TURBINE OPERATION
A wind turbine or aerogenerator is essentially a sophisticated windmill, similar to those still used in many rural areas for pumping water from deep wells and powering small agricultural or industrial machinery. However, the domestic windmill may only be 30 to 50 feet high and have as many as 12 blades with a rotor diameter of 20 feet or so, whereas the average wind energy tower may be more than 300 feet tall and be fitted with three blades, each 100 feet or more in length. These wind turbines may be situated along hilltops, on flat plains, or even at sea.
This fairly recent technology has taken hold in more than 80 countries around the world, led by the United States and closely followed by Germany, China, and Spain. Although the “fuel” that powers these turbines (wind) is free, the expenditures needed to make installations reasonably profitable are considerable.
The operating principles are basic. Wind blowing though the blades makes them rotate and turn the shaft of an electric power generator situated inside an elevated compartment, called a nacelle (Figures 1, 2). Inside the nacelle are other controls such as brakes, rotor pitch controllers, gearboxes, and fire protection equipment (Figure 3). As the blades rotate, they produce energy, which turns the gears and reducers, which turn the generator’s torque shaft. The generator produces energy, which is then transmitted from the tower to transformer stations through high-tension power lines for distribution.
|Figure 1. Wind Turbine Tower|
|Figures 1-3 courtesy of author.|
|Figure 2. Tower Interior|
|Figure 3. Nacelle Interior|
The towers are normally situated in groups called wind farms in areas where winds are constant with small variation in direction and speed. Wind farms may cover several hundred acres and are usually situated along hilltops and similar elevated areas. Prior to erecting the towers, viability studies are made in a number of alternative locations to ascertain which would be the most ideal. Land acquisition, either by outright purchase or long-term leasing follows, with access road construction, ground preparation, tree and other obstacle removal, and leveling completed before transporting the components to the site.
The road transport of the components is in itself quite an operation, since sections of the towers can be some 60 or more feet long and more than 12 feet in diameter. An average tower will have four to five vertical sections. The blades can be as long as 130 feet, although the most common blades are about 100 feet long. Once on site, cranes raise the tower shafts, situate the nacelle and generator components, and mount the blades. Construction can take several weeks; often several months; and more than a year, depending on the number of generators to be erected. The average total cost of one aerogenerator, including engineering, construction, erection, and start-up, can be around $1.5 million, although complications in location, erection, and other costs can elevate the total to well over $3 million.
Standard operating procedures/guidelines (SOPs/SOGs) for emergency operations at wind turbine sites are absolutely necessary. The turbine-supporting tower can be as much as 300 feet high with very slim access shafts (generally no elevators, just vertical ladders) and extremely confined interiors. Although a few towers may be equipped with elevators, they would be very tight spaces. They could be used where available for lifting some rescue personnel and equipment up to the nacelle, although it would be difficult to lower a victim unless that person could be evacuated in a standing position.
High-angle rescue techniques are the most appropriate, but they must incorporate very specific actions.
Spain ranks fourth in the world in wind power production; several Spanish companies are recognized world leaders in the engineering, design, and construction of wind turbines. The Navarra region has the country’s highest concentration of aerogenerators. Recognizing the need for emergency response procedures, the Navarra Emergency Response Agency, in close cooperation with the Spanish affiliate of General Electric, one of the country’s leading aeolic energy providers, developed a very precise SOP for emergency response to incidents involving wind turbines at any height as well as the surrounding wind farm site (see sidebars “Wind Turbine Emergency Procedure” and “Wind Turbine Rescue”). The 12-station agency has more than 1,000 employees and protects a 3,861 square-mile area with 630,500 residents. The adaptation of the Navarra SOP below provides a guideline for all fire departments worldwide in developing specific SOPs/SOGs for emergency response to incidents involving wind turbines.
Fire and personal injury are the principal emergency situations that could affect a wind turbine and require emergency service response. These two overall categories encompass many variants that require specific response procedures. Added to the high initial costs of engineering and construction, damages to a wind turbine could well run up to hundreds of thousands of dollars in repairs and reconstruction, in addition to many months of downtime and subsequent loss of income.
The Caithness Windfarm Information Forum, based in the United Kingdom, compiled a summary of more than 900 incidents involving wind turbines.1
In a December 2009 incident in Uelzen, Germany, a fire occurred in a wind turbine at a height of 130 meters (427 feet). The fire department closed off the the area and allowed the fire to burn out because it could not fight the fire at that height and had no other choice.
Lightning strikes damaged wind turbines on the Campo Indian Reservation in California in August 2009, severely damaging two of them.
At the same installation, in April 2010, a wind-farm worker who suffered an electrical shock was airlifted to safety.
Lightning struck a turbine that was offline for repairs at the Elkhorn Ridge wind farm near Bloomfield, Nebraska, in August 2010. There were no injuries. The Bloomfield Fire Department responded to the emergency call, but the small fire burned itself out. In late 2008, an explosion and fire in a turbine injured three workers during construction of the wind farm.
In August 2010, the Hatchet Fire burned five acres near wind turbines before crews contained it. The fire occurred west of Hatchet Ridge, California.
The most recent wind turbine emergency at this writing occurred in December 2010 at the Pouille-les-Coteaux wind farm in France. The report said that firefighters had to rescue an injured 22-year-old maintenance technician by lowering him 98 meters (322 feet) in freezing temperatures.
The interior dimensions of wind turbines vary among manufacturers, but in general they are all pretty tight. Mounted on the top of the tower, the nacelle contains the electricity-generating equipment that is connected to the turbine blades. In general, a typical nacelle is approximately 30 feet long, between 7½ and 8 feet high, and around 9½ to 11 feet wide. An “average” man—six feet tall with a trim build—would have to crouch and bend himself in pretty much all interior spaces. The largest open area is around the service hoist and around the drive shaft. Some blade manufacturers claim that their blades are accessible, but they don’t describe the physical characteristics necessary to get into the blades. The blades are one of the problematic spaces for possible entrapment.
The average tower diameters are between 14 and 15 feet at ground level, about 12 feet at midheight, and between seven and 10 feet at the top where the nacelle is mounted. Tower heights can range from 150 feet up to 330 feet; some more recent generation towers are even higher.
Fires can occur in distinct locations and heights and may involve various fuels and ignition sources. The wind tower’s primary objective is to produce electricity. Hence, a number of possible ignition sources exist from ground level and in more than a few wind farms, from underground levels up to more than 300 feet above ground.
Fuels can include electrical cables, plastics, and even textiles, any and all of which can also be found at all heights. Since the construction materials used in these towers and their components will invariably include plastics and possibly some combustible metals (e.g., titanium and aluminum, among others), as well as relatively easily deformable metallic structural and enclosure materials, the consequences of a fire in a wind turbine can be disastrous.
Also, a fire in a turbine assembly can propagate to surrounding vegetation and produce a wildland fire risk, and a fire involving surrounding vegetation could pose a threat to the wind farm.
The origins of fires in wind generators are numerous and in some instances almost inevitable. Statistics show that the major cause of fires in aerogenerators is lightning. Although aerogenerators include lightning arresters and other elements to reduce the potential of ignition from lightning strikes, they do not completely eliminate possible lightning damage.
Another frequent cause of fires is the mechanical friction among the multiple moving parts of the turbine assembly, gears, shafts, and other moving or rotating metal components that may provoke sparking. Since the average wind turbine may contain more than 200 gallons of hydraulic fluid plus variable quantities of other lubricants and similar combustible liquids, there’s no shortage of fuel.
Electrical short circuits can occur in numerous locations, anywhere from the windmill’s top to the base. Fires in wind turbines are known to contribute to structural failure and collapse.
The major inconvenience at wind farms in regard to possible fires is that most of these installations are unattended. The operating companies have technicians available within reasonable distances, but they are not usually present, except during periodic inspections or maintenance operations. Fire protection at wind farms and inside the aerogenerators depends entirely on automatic fire detection and extinguishment systems, with reliable and constant supervision at one or more fixed locations. Detection is usually multidisciplinary, including early detection—fast response systems coupled with self-contained automatic extinguishing systems such as water mist or inert gases. The detection systems, usually networked and requiring detection/confirmation of a fire, instantaneously communicate the alarm to the supervision station and simultaneously activate the extinguishing system. The supervision of the detection and extinguishing systems must be full-time and be able to clearly and concisely communicate complete information to responsible emergency responding agencies.
Responding fire departments may normally be several miles away and have to travel over roads that quite often require all-wheel-drive vehicles. The primary limiting factors to fire department intervention are the height of the fire and the extremely limited vertical access inside the tower. A fire actively fought, controlled, and extinguished by fire department personnel would be a rare event. The general rule established in SOPs is not to attempt to physically attack a fire inside the tower and generator assembly but instead to rely on the fixed installations. At the same time, it would be necessary to establish an exterior defensive attack to protect exposed structures and vegetation near the affected tower.
It is absolutely imperative that emergency responders interact with the wind turbine operators to create, implement, and maintain preemergency response planning. Responders should go to the site to familiarize themselves with the facilities and develop simulation emergency exercises with the operators.
Human injury rescue operations are another matter. Emergencies involving physical injury to operational and maintenance personnel occasionally present in and around the wind generators (mainly falls and similar accidents) and will inevitably require high-angle rescue techniques and tactics, since an injured operator may be more than 300 feet above ground and inside very tight confined spaces that have extremely limited access. These possible rescue situations are addressed in the detailed Navarra Emergency Agency SOPs/SOGs below.
NAVARRA EMERGENCY AGENCY WIND TURBINE EMERGENCY RESPONSE SOPs/SOGs
Hazards.Since an emergency situation involves electricity-generating systems situated at heights of from 120 to more that 300 feet above ground, including mechanical devices with multiple moving components, you must consider the following basic hazards: possible falls from great heights, the risk of electrocution, and entrapment.
Personal protective equipment (PPE) for each responder should include an approved harness, a dynamic anchoring rope, safety shackles, an adequate helmet, and gloves.
Team PPE should include the following:
- Rucksacks or bags with high-angle equipment (descenders, rope clamps, carabiners, pulleys, shackles, tape, protectors, and so on).
- Antifall devices for 8-mm steel cable, provided by the owner of the site, or dynamic rescue rope equipment for fall protection.
- Static and dynamic rope in lengths sufficient to access the height of the machinery (nacelle and blades). Alternately, sufficient lengths of rope that can be tied together, ensuring that the knots will pass through descenders and pulleys.
- A stretcher (backboard or stokes basket) that can be used horizontally or vertically. A confined-space stretcher may be necessary in very confined spaces, such as inside the nacelle or propeller blades.
Other equipment includes a flashlight and a two-way radio certified for use in confined spaces that have metallic enclosures.
Possible emergencies may include entrapment by mechanical elements in the nacelle, electrical shock, persons who have collapsed (e.g., fainted, suffered a heart attack or a similar ailment) or fallen inside the hub or tower, fire, and falls from the exterior wind turbine structure.
Overall personnel safety measures include the following:
- Before commencing operations, ensure that machinery is shut down and that no machinery will be started up during emergency operations.
- Shut off electrical power to the aerogenerator.
- Always maintain antifall equipment connections while working where falls might occur, even inside the nacelle.
During any emergency situation involving aerogenerators, a company maintenance operator must be present.
Aerogenerators have numerous anchorage points. In an evacuation by stretcher, it will be necessary to alternate between horizontal and vertical positions. The horizontal is a must for exiting the nacelle (exterior) or for crossovers inside the tower tube.
Wind turbine towers range from 120 to more than 300 feet in height, and even higher towers are in design. Hence, you must consider the possibility of evacuation from heights greater than the lengths of the rescue ropes. If ropes must be tied together to obtain the needed length, you must ensure that knots can pass through eyes.
Alarm reception.The recipient of the initial and follow-up alarm communications for emergencies involving wind turbines must obtain the following information and supplement it as the situation evolves:
- Incident type: Fall, entrapment, fire.
- Incident location: Wind farm site and number of the aerogenerator involved.
- Number of victims, their locations, and conditions.
- Access to the wind farm and the particular aerogenerator.
- Weather conditions.
- Any additional information.
For fire in an aerogenerator, do the following:
- Confirm disconnection of electrical power from other machinery or a substation.
- Establish a safety perimeter of 750 feet around the involved tower for possible falling components.
- Prevent spread of fire to surrounding vegetation or other exposures.
1. Caithness Windfarm Information Forum, “Wind Turbine Accident Compilation,” http://www.caithnesswindfarms.co.uk/fullaccidents.pdf.
GEORGE H. POTTER is a Spanish fire service instructor and a board member of the Spanish Firefighters Association (ASELF). A resident of Spain for almost 50 years, he has worked with fire protection systems, mobile fire apparatus, and training public service firefighters and officers and industrial emergency responders. Potter is a former Anne Arundel County, Maryland, volunteer firefighter and a United States Air Force crash rescue firefighter. He leads a working group in the firefighters’ association dedicated to developing and coordinating fire service response procedures to emergencies in wind turbines.
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