BENEFITS : LOW ↔ IMPACTS : HIGH

Resource Documents: Safety (50 items)

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Date added: January 6, 2023
Norway, Safety •

Ice throw from wind turbines: Assessment and risk management

Author: Bredesen, Rolv

[excerpts]

What is in-cloud icing?

If temperatures are below 0°C and the structure is located inside a cloud (above cloud base height) we get in-cloud icing.

The ice accretion rates increases with the relative windspeed and the moisture content of the cloud.

Because the blade of a wind turbine moves fast there is an elevated hazard associated with ice throw and fall from turbines located in icing conditions.

How far can the ice be thrown?

Maximum throw distance (screening) : 1.5 × (Diam. + Ht.). ~ 350 m.*

Ice debris have so far not been found at this distance.

Ice pieces have been found at 68 % of the maximum throw distance.

1.4 × tip height (Cattin). 1000 ice pieces with 3 % above tip height

1 × tip height (Lunden, 2017). 500 ice pieces total.

*Strict German/Austrian regulations

Seifert screening formula of danger zone: (Hubheiht + rotordiameter) × 1.5

In Germany/Austria it is required to have ice detection systems if there are roads or buildings within this distance.

Restriction on production: turbine must stop when there is icing.

If detection systems are reliable and sensitive, then the potential hazard is most likely associated with ice fall and not throw of smaller ice pieces.

How dangerous is the ice?

An impact kinetic energy of more than 40 J is considered fatal.

40 J correpsonds to a 0.2 kg ice piece with density 500 g/dm³ falling from an elevation of 30–50 m.

Because of the turbine height all ice pieces larger than approximately 0.2 kg are potentially fatal.

How large a risk can we accept?

Localized individual risk metric: the probability that an average unprotected person, permanently present at a specified location, is killed in a period of one year due to an accident at a hazardous installation

Acceptable risk:

Ski tracks, hiking areas < 10⁻⁴

People walking along public road, industrial sites, scattered houses < 10⁻⁵

Houses, cafés, shops, etc. < 10⁻⁶

Schools, kindergartens, shopping malls, hospitals, etc. < 10⁻⁷

See also: R.E. Bredesen, H. Farid, M. Pedersen, D. Haaheim, S. Rissanen, G. Gruben and A. Sandve, “IceRisk: Assessment of risks associated with ice throw from wind turbine blades” (PO.339). https://windeurope.org/summit2016/conference/allposters/PO339.pdf, in WindEurope Summit, Hamburg, 2016.

Rolv Erlend Bredesen, Kjeller Vindteknikk
IEA Wind Task 19, Winterwind 2017
February 15, 2017

Download original document: “Ice throw from wind turbines: Assessment and risk management”

Date added: November 14, 2019
Safety, U.S. •

Wind Farms and Public Use Airports – Why the FAA Fails to Ensure Air Safety

Author: Armstrong, Alan

The explosion of wind turbine developments across the United States does not bode well for the continued viability of many public use airports.

OVERVIEW OF THE PROBLEM

Increasingly, wind farms with wind turbine generators (WTGs) nearly 500 feet above ground level litter the landscape. However, the disturbing reality is that these wind farms are being built in close physical proximity to public use airports. Because of their height and their interference with radar sites used by air traffic control and interference with normal traffic flow patterns, the construction of wind farms near public use airports is an existential threat to those airports. The erection of wind turbine generators near public use airports invariably leads to the following:

Interference with radar used to provide radar services to pilots operating aircraft in and out of the airport with “clutter” and other signal disturbances having an adverse impact on the ability of air traffic control to provide services to pilots;

Alterations of the traffic flow for VFR traffic operating in and out of the airport resulting in a “bottle neck” of traffic flow with a concomitant loss of separation between aircraft and the WTGs and aircraft and other aircraft;

Penetrations of “imaginary surfaces” designed to assure pilots operating aircraft separation from fixed objects such as WTGs and antennae that may present collision hazards in low visibility conditions;

An increase in the climb gradient for aircraft departing the airport in an effort to prevent departing aircraft from impacting the WTGs; and

An increase in the minimum descent altitudes and/or decision heights at which pilots may operate their aircraft when conducting instrument approach procedures into the airport.

The net result of these adverse effects is to make the airport a less safe and efficient destination whether for flight training purposes, refueling, or remaining overnight. Consequently, pilots, based upon their interest in self-preservation and the desire to avoid being impaled in the blades of a wind turbine generator, will select airports other than airports surrounded by wind turbine generators for fuel stops, remaining overnight, and for flight training purposes.

Although the airport sponsor has an obligation under FAA Sponsor Grant Assurance No. 20 to keep the approaches and departures from the airport safe and clear of obstructions, the reality is that the FAA Obstacle Evaluation Group overrides those concerns and invariably rules in favor of the wind farm developer by issuing a Determination of No Hazard (DNH). In the DNH, the FAA will concede that the wind turbine generators interfere with radar, elevate the minimum descent altitudes, require increased climb gradients, and the host of other problems, but will still conclude there are no “adverse consequences” to the erection of wind turbine generators in close physical proximity to a public use airport. This simply is a reality. The FAA Obstacle Evaluation Group invariably finds in favor of the developer and demonstrates no interest in protecting the safety of the airport, even though the airport sponsor has promised the FAA Airports Division to keep the airport safe and free of obstructions.

HOW THE GAME IS PLAYED

The developer of a wind farm is required to file with the FAA a Form 7460-1 if the wind farm will be built in the vicinity of a public use airport. Generally, in response to the filing of the form, the FAA renders a Notice of Presumed Hazard (NPH). The NPH catalogs all the problems the erection of the wind farm will present to the airport such as increasing the climb gradients, increasing the minimum descent altitudes, adverse impact on radar facilities employed by air traffic control in providing radar services to pilots operating to and from the airport, and a host of other problems that are presented by the erection of WTGs in the vicinity of the airport. However, the Obstacle Evaluation Group of the FAA invariably states in the NPH that a different result might be achieved if an aeronautical study were conducted. An aeronautical study is conducted pursuant to 49 U.S.C. §44718, 14 C.F.R. §77.29, and FAA Order JO 7400.2M, Procedures for Handling Airspace Matters (“the Handbook”). The aeronautical study is supposed to consider the impact on arriving and departing IFR and VFR flights, the impact on the public use airport, the impact on traffic capacity at the airport or planned airports, the impact on the minimum obstacle clearance altitudes, the minimum flight instrument rules altitudes, the impact on approved or planned instrument approach procedures and departure procedures, the potential effect on ATC radar including the physical or electromagnetic effects on air navigation facilities, and the cumulative effect of the wind turbine generators when combined with the effects of other existing or proposed structures.

While there are clear, engineering and scientific principles in determining whether structures are obstructions to air navigation, those clear, empirical considerations vanish with the execution of an aeronautical study which gives the person conducting the study the latitude to determine whether or not obstructions to air navigation that penetrate imaginary surfaces have an “adverse effect” on safety. While the FAA pretends in the Handbook that its primary objective is to ensure safety in air navigation, in reality its primary goal is to enable developers of wind turbine generators and others who create obstructions to air navigation to put their structures in place. In fact, the conciliatory nature with which the Obstacle Evaluation Group views penetrations to imaginary surfaces is borne out by the fact that it seeks to resolve the issues through “negotiations” with the sponsor. Why is this? The answer is simple. The FAA does not want to spend its precious resources fighting with developers of wind turbine generators. That economic burden falls on the city or county that owns the airport or on public interest groups that seek to preserve and protect the airport. That is of no concern to the FAA. Moreover, while the airport sponsor must keep the approaches and departure surfaces of the airport safe and free of obstructions to comply with the Sponsor Grant Assurances, the Obstacle Evaluation Group frequently frustrates those obligations and responsibilities of the airport sponsor.

It is troubling that the FAA views itself as an enabler of developers who seek to construct wind turbine generators. However, this is a reality. Moreover, time and time again, the FAA has been reversed because it has demonstrated it does not understand its own Handbook. This is precisely what happened in Town of Barnstable, Massachusetts v. Federal Aviation Administration, 659 F.3d 28, 36 (D.C. Cir. 2011) where the FAA was reversed and the United States Court of Appeals for the District of Columbia declared:

The FAA repeatedly notes in its brief that the Handbook “largely consists of criteria rather than rules to follow.” Respondent’s Br. at 40. We agree. Any sensible reading of the Handbook, and of §6-3-8(c)(1) in particular, would indicate there is more than one way in which the wind farm can pose a hazard to VFR operations. Indeed, other sections of the Handbook, especially when read in light of some of the evidence noted above, suggest that the project may very well be such a hazard. Here, by abandoning its own established procedure, see D&F Alfonso Realty Trust v. Garvey, 216 F.3d 1191, 1197 (D.C. Cir. 2000), the FAA catapulted over the real issues and the analytical work required by its Handbook.

659 F.3d at 36.

THE STATE COURT OPTION

The laws in the various jurisdictions vary. In some states, if the FAA issues a determination of no hazard, the state officials rubber-stamp the FAA determination and issue a permit to erect the wind turbine generators. Further, in some states, there are local airport authorities with airport zoning rules, and until and unless the wind turbine generator developer obtains a determination of no hazard, a variance from the zoning ordinances cannot be obtained. On the other hand, in the State of Iowa, even though there is a determination of no hazard, the local airport zoning board can preclude the erection of an obstruction in navigable airspace, a fact borne out by the decision of the Supreme Court of Iowa In the Carroll Airport Commission v. Danner, 927 N.W.2d 635 (IA 2019). The Iowa Supreme Court reasoned that the FAA airspace regulations do not occupy the field to such an extent that the field is preempted by FAA regulations and further concluded that regulating navigable airspace is a joint endeavor between the FAA and state government.

SUMMARY AND CONCLUSION

The explosion of wind turbine developments across the United States does not bode well for the continued viability of many public use airports. The operators of those airports are going to have to appreciate the legal and regulatory milieu in which they find themselves and garner the resources to combat the proliferation of wind turbine generators in and around their airports. Otherwise, their airports may face extinction.

Alan Armstrong
Oct 17, 2019
alanarmstronglaw.com

Date added: November 3, 2018
Ontario, Safety •

Wind Turbine Public Safety Risk, Direct and Indirect Health Impacts

Author: Palmer, William

Abstract —
Wind turbines are often perceived as benign. This can be attributed to the population majority dwelling in urban locations distant from most wind turbines. Society may understate the risk to individuals living near turbines due to an overstatement of the perceived benefits of turbines, and an understatement of the risk of injury from falling turbine parts, or shed ice. Flaws in risk calculation may be attributed to a less than fully developed safety culture. Indications of this are the lack of a comprehensive industry failure database, and safety limits enabling the industry growth, but not protective of the public. A comprehensive study of wind turbine failures and risks in the Canadian province of Ontario gives data to enable validation of existing failure models. Failure probabilities are calculated, to show risk on personal property, or in public spaces. Repeated failures, and inadequate safety separation show public safety is not currently assured. A method of calculating setbacks from wind turbines to mitigate public risk is shown. Wind turbines with inadequate setbacks can adversely impact public health both directly from physical risk and indirectly by irritation from loss of safe use of property. Physical public safety setbacks are separate from larger setbacks required to prevent irritation from noise and other stressors, particularly when applied to areas of learning, rest and recuperation. The insights provided by this paper can assist the industry to enhance its image and improve its operation, as well as helping regulators set safety guidelines assuring protection of the public.

William K.G. Palmer, Journal of Energy Conservation – 2018;1(1):41-78

Download original document: “Wind Turbine Public Safety Risk, Direct and Indirect Health Impacts”

Date added: March 2, 2018
Safety •

Analysis of throw distances of detached objects from horizontal-axis wind turbines

Author: Sarlak, Hamid; and Sørensen, Jens

Figures 4 to 6 show the results for different-size blade pieces from different-size turbines at different wind speeds and blade tip speeds. For normal tip speeds (figs 4 and 5), the potential blade throw distance for a 2.3-MW turbine was calculated to be ~500 m (1,640 ft) and for a 5-MW turbine ~900 m (2,953 ft). At “extreme” tip speeds (fig 6) the corresponding distances were 800 m (2,625 ft) and 1500 m (4,921 ft).

[ABSTRACT] This paper aims at predicting trajectories of the detached fragments from wind turbines, in order to better quantify consequences of wind turbine failures. The trajectories of thrown objects are attained using the solution to equations of motion and rotation, with the external loads and moments obtained using blade element approach. We have extended an earlier work by taking into account dynamic stall and wind variations due to shear, and investigated different scenarios of throw including throw of the entire or a part of blade, as well as throw of accumulated ice on the blade. Trajectories are simulated for modern wind turbines ranging in size from 2 to 20 MW using upscaling laws. Extensive parametric analyses are performed against initial release angle, tip speed ratio, detachment geometry, and blade pitch setting. It is found that, while at tip speeds of about 70 m/s [157 mph] (normal operating conditions), pieces of blade (with weights in the range of approximately 7-16 ton) would be thrown out less than 700 m for the entire range of wind turbines, and turbines operating at the extreme tip speed of 150 m/s [336 mph] may be subject to blade throw of up to 2 km from the turbine. For the ice throw cases, maximum distances of approximately 100 and 600 m are obtained for standstill and normal operating conditions of the wind turbine, respectively, with the ice pieces weighing from 0.4 to 6.5 kg. The simulations can be useful for revision of wind turbine setback standards, especially when combined with risk assessment studies.

Hamid Sarlak and Jens N. Sørensen
Section of Fluid Mechanics, Department of Wind Energy, Technical University of Denmark, Lyngby, Denmark

Wind Energy 2016; 19:151–166. DOI: 10.1002/we.1828

Download original document: “Analysis of throw distances of detached objects from horizontal-axis wind turbines”

See also:

“A method for defining wind turbine setback standards” by Jonathan Rogers, Nathan Slegers, and Mark Costello, Wind Energy 2012; 15:289–303. (463 m [1,519 ft] for a Vestas 2-MW turbine)

“Analysis of blade fragment risk at a wind energy facility” by Scott Larwood and David Simms, Wind Energy (published online 6 April 2018). “The results showed that a setback to property lines of 2 times the overall turbine height would be acceptable. However, the setback to dwellings should probably be increased from 3 to 3.5 times the overall turbine height for an acceptable risk.”

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