# Wind Turbine Sound and Health Effects An Expert Panel Review

Prepared by (in alphabetical order):



## W. David Colby, M.D. Robert Dobie, M.D. Geoff Leventhall, Ph.D. David M. Lipscomb, Ph.D. Robert J. McCunney, M.D. Michael T. Seilo, Ph.D. Bo Søndergaard, M.Sc.

Prepared for:



## American Wind Energy Association

and 

## Canadian Wind Energy Association

December 2009

# Contents

iii Section Page Executive Summary ............................................................................................................. ........ES-1

1 Introduction................................................................................................................... ......1-1 1.1 Expert Panelists.......................................................................................................1-1 1.2 Report Terminology...............................................................................................1-2

2 Methodology .................................................................................................................... ...2-1 2.1 Formation of Expert Panel ....................................................................................2-1 2.2 Review of Literature Directly Related to Wind Turbines.................................2-1 2.3 Review of Potential Environmental Exposures..................................................2-1

3 Overview and Discussion.................................................................................................3-1 3.1 Wind Turbine Operation and Human Auditory Response to Sound.............3-1 3.1.1 Overview ....................................................................................................3-1 3.1.2 The Human Ear and Sound .....................................................................3-2 3.1.3 Sound Produced by Wind Turbines .......................................................3-3 3.1.4 Sound Measurement and Audiometric Testing....................................3-5 3.2 Sound Exposure from Wind Turbine Operation ...............................................3-6 3.2.1 Infrasound and Low-Frequency Sound .................................................3-6 3.2.2 Vibration .....................................................................................................3-9 3.2.3 Vestibular System....................................................................................3-11 3.3 Potential Adverse Effects of Exposure to Sound .............................................3-12 3.3.1 Speech Interference .................................................................................3-12 3.3.2 Noise-Induced Hearing Loss .................................................................3-13 3.3.3 Task Interference .....................................................................................3-13 3.3.4 Annoyance................................................................................................3-13 3.3.5 Sleep Disturbance....................................................................................3-13 3.3.6 Other Adverse Health Effects of Sound ...............................................3-13 3.3.7 Potential Health Effects of Vibration Exposure ..................................3-14 3.4 Peer-Reviewed Literature Focusing on Wind Turbines, Low-Frequency Sound, and Infrasound ........................................................................................3-15 3.4.1 Evaluation of Annoyance and Dose -Response Relationship of Wind Turbine Sound .........................................................................................3-15 3.4.2 Annoyance................................................................................................3-16 3.4.3 Low-Frequency Sound and Infrasound ...............................................3-17

4 Results ........................................................................................................................ ..........4-1 4.1 Infrasound, Low-Frequency So und, and Annoyance .......................................4-1 4.1.1 Infrasound and Low-Frequency Sound .................................................4-2 4.1.2 Annoyance..................................................................................................4-2 4.1.3 Other Aspects of Annoyance ...................................................................4-3 4.1.4 Nocebo Effect .............................................................................................4-4CONTENTS, CONTINUED

Section Page

iv 4.1.5 Somatoform Disorders ............................................................................. 4-4 4.2 Infrasound, Low-frequency Sound and Disease ............................................... 4-5 4.2.1 Vibroacoustic Disease............................................................................... 4-5 4.2.2 High-Frequency Exposure....................................................................... 4-6 4.2.3 Residential Exposure: A Case Series ...................................................... 4-6 4.2.4 Critique....................................................................................................... 4-7 4.3 Wind Turbine Syndrome ...................................................................................... 4-8 4.3.1 Evaluation of Infrasound on the Vestibular System ............................ 4-8 4.3.2 Evaluation of Infrasound on Internal organs........................................ 4-9 4.4 Visceral Vibratory Vestib ular Disturbance ...................................................... 4-10 4.4.1 Hypothesis ............................................................................................... 4-10 4.4.2 Critique..................................................................................................... 4-11 4.5 Interpreting Studies and Reports....................................................................... 4-11 4.6 Standards for Siting Wind Turbines.................................................................. 4-13 4.6.1 Introduction ............................................................................................. 4-13 4.6.2 Noise Regulations and Ordinances ...................................................... 4-13 4.6.3 Wind Turbine Siting Guidelines........................................................... 4-13

5 Conclusions.................................................................................................................... ..... 5-1

6 References ..................................................................................................................... ...... 6-1
Appendices

A Fundamentals of Sound B The Human Ear C Measuring Sound D Propagation of Sound E Expert Panel Members

Tables

1-1 Definitions of Ac oustical Terms........................................................................................ 1-2 3-1 Typical Sound Pressure Levels Measur ed in the Environment and Industry ........... 3-2 3-2 Hearing Thresholds in the Infr asonic and Low Frequency Range ............................. 3-7

Figures 3-1 Sound Produced by Wind Turbine Flow......................................................................... 3-4 3-2 Hearing Contours for Equal Loudness Level (ISO:226, 2003) ...................................... 3-9 3-3 Comparison of Excitation of an Ob ject by Vibration and by Sound.......................... 3-10 C-1 Weighting Networks ........................................................................................................ . C-2V 

# Acronyms and Abbreviations

μPa microPascal ACOEM American College of Occupational and Environmental Medicine ANSI American National Standards Institute AWEA American Wind Energy Association ASHA American Speech-Lang uage-Hearing Association CanWEA Canadian Wind Energy Association dB decibel dBA decibel (on an A-weighted scale) DNL day-night-level DSM-IV-TR Diagnostic and Statistical Manual of Mental Disorders , Fourth Edition EPA U.S. Environmental Protection Agency FDA Food and Drug Administration FFT Fast Fourier Transform GI gastrointestinal HPA Health Protection Agency Hz Hertz IARC International Agency for Research on Cancer ICD-10 International Statistical Classifi cation of Diseases and Related Health Problems, 10th Revision IEC International Engineering Consortium ISO International Organization for Standardization Km kilometer kW kilowatt L eq equivalent level LPALF large pressure amplitude and low frequency m/s meters per second m/s 2 meters per second squared NIESH National Institute of Environmental Health Sciences NIHL noise-induced hearing loss NIOSH National Institute for Occupational Safety and Health N/m 2 Newtons per square meter NRC National Research Council NTP National Toxicology Program ONAC Office of Noise Abatement and Control OSHA Occupational Safety and Health Administration Pa Pascal UK United Kingdom VAD vibroacoustic disease VVVD vibratory vestibular disturbance VEMP vestibular evoked myogenic potential response WHO World Health OrganizationES-1 

# Executive Summary

People have been harnessing the power of the wind for more than 5,000 years. Initially used widely for farm irrigation and millworks, toda y’s modern wind turbines produce electricity in more than 70 countries. As of the end of 2008, there were approximately 120,800 megawatts of wind energy capacity insta lled around the world (Global Wind Energy Council, 2009). Wind energy enjoys considerable public support , but it also has its detractors, who have publicized their concerns that the sounds emi tted from wind turbines cause adverse health
consequences. In response to those concerns, the Amer ican and Canadian Wind Energy Associations (AWEA and CanWEA) established a scientific advisory panel in early 2009 to conduct a review of current literature available on the issue of perceived health effects of wind turbines. This multidisciplinary panel is co mprised of medical doctors, audiologists, and acoustical professionals from the United States, Canada, Denmark, and the United Kingdom. The objective of the panel was to pr ovide an authoritative reference document for legislators, regulators, and anyone who wants to make sense of the conflicting information about wind turbine sound. The panel undertook extensive review, analysis , and discussion of the large body of peerreviewed literature on sound and health effects in general, and on sound produced by wind turbines. Each panel member contributed a un ique expertise in audiology, acoustics, otolaryngology, occupational/ environmental medi cine, or public health. With a diversity of perspectives represented, the panel assessed th e plausible biological effects of exposure to wind turbine sound. Following review, analysis, and discussion of current knowledge, the panel reached consensus on the following conclusions:

• There is no evidence that the audible or su b-audible sounds emitted by wind turbines have any direct adverse physiological effects.

• The ground-borne vibrations from wind turbin es are too weak to be detected by, or to affect, humans.

• The sounds emitted by wind turbines are no t unique. There is no reason to believe, based on the levels and frequencies of the so unds and the panel’s experience with sound exposures in occupational settings, that the sounds from wind turbines could plausibly have direct adverse health consequences.1-1 SECTION 1 

# Introduction

The mission of the American Wind Energy Association (AWEA) is to promote the growth of wind power through advocacy, communication, and education. Similarly, the mission of the Canadian Wind Energy Association (CanWEA ) is to promote the responsible and sustainable growth of wind power in Canada. Both organizations wish to take a proactive role in ensuring that wind energy projects ar e good neighbors to the communities that have embraced wind energy. Together AWEA and CanWEA proposed to a number of independent groups that they examine the scientific validity of recent reports on the adverse health effects of wind turbine proximity. Such reports have raised public concern about wind turb ine exposure. In the absence of declared commitment to such an effort from independent groups, the wind industry decided to be proactive and address the issue itself. In 2009, AWEA and CanWEA commissioned this report. They asked the author s to examine published scientific literature on possible adverse health effects result ing from exposure to wind turbines. The objective of this report is to address he alth concerns associated with sounds from industrial-scale wind turbines. Inevitably, a re port funded by an industry association will be subject to charges of bias and conflicts of interest. AWEA and CanWEA have minimized bias and conflicts of interest to the greatest possible extent through selection of a distinguished panel of independent experts in acoustics, audiology, medicine, and public health. This report is the result of their efforts.



# 1.1 Expert Panelists

The experts listed below were asked to investigate and analyze existing literature and publish their findings in this report; their current positions and/or qualifications for inclusion are also provided.

• W. David Colby, M.D. : Chatham-Kent Medical Officer of Health (Acting); Associate Professor, Schulich School of Medicine & Dentistry, University of Western Ontario

• Robert Dobie, M.D. : Clinical Professor, University of Texas, San Antonio; Clinical Professor, University of California, Davis

• Geoff Leventhall, Ph.D .: Consultant in Noise Vibration and Acoustics, UK

• David M. Lipscomb, Ph.D .: President, Correct Service, Inc.

• Robert J. McCunney, M.D. : Research Scientist, Massachus etts Institute of Technology Department of Biological Engineering; Sta ff Physician, Massachusetts General Hospital Pulmonary Division; Harvard Medical School

• Michael T. Seilo, Ph.D .: Professor of Audiology, Western Washington UniversityWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

1-2 • Bo Søndergaard, M.Sc. (Physics ): Senior Consultant, Dani sh Electronics Light and Acoustics (DELTA) Mark Bastasch, an acoustical engineer with th e consulting firm of CH2M HILL, acted as technical advisor to the panel.



# 1.2 Report Terminology

Certain terms are used frequently throughout th is report. Table 1-1 defines these terms. An understanding of the distinction between “sound” and “noise” may be particularly useful to the reader.

TABLE 1-1 Definitions of Acoustical Terms
Term Definitions

Sound Describes wave-like variations in air pr essure that occur at frequencies that can stimulate receptors in the inner ear and, if sufficiently powerful, be appreciated at a conscious level.

Noise Implies the presence of sound but also implies a response to sound: noise is often defined as unwanted sound.

Ambient noise level The composite of noise from all sources near and far. The normal or existing level of environmental noise at a given location.
Decibel (dB) A unit describing the amplitude of sound, equal to 20 times the logarithm to the base 10 of the ratio of the measured pressure to the reference pressure, which is 20 micropascals (μPa).
A-weighted sound pressure level (dBA) The sound pressure level in decibels as measured on a sound level meter using the A-weighted filter network. T he A-weighted filter de-emphasizes the very low and very high frequency components of the sound in a manner similar to the frequency response of the human ear and correlates well with subjective reactions to noise.
Hertz (Hz) A unit of measurement of frequency; t he number of cycles per second of a periodic waveform.

Infrasound According to the International Electrotechnical Commission’s (IEC’s) IEC1994, infrasound is: Acoustic oscillations whose frequency is below the lowfrequency limit of audible sound (about 16 Hz). However this definition is incomplete as infrasound at high enough levels is audible at frequencies below 16 Hz. (IEC (1994): 60050-801:1994 Internatio nal Electrotechnical Vocabulary - Chapter 801: Acoustics and electroacoustics).
Low-frequency sound Sound in the frequency range that overlaps the higher infrasound frequencies and the lower audible frequenc ies, and is typically considered as 10 Hz to 200 Hz, but is not closely defined. Source: HPA, 2009.2-1 SECTION 2 

# Methodology

Three steps form the basis for this report: form ation of an expert panel, review of literature directly related to wind turbines, and revi ew of potential environmental exposures.



# 2.1 Formation of Expert Panel

The American and Canadian wind energy asso ciations, AWEA and CanWEA, assembled a distinguished panel of independent experts to address concerns that the sounds emitted from wind turbines cause adverse health consequences. The objective of the panel was to provide an au thoritative reference document for the use of legislators, regulators, and people simply wanting to make sense of the conflicting information about wind turbine sound. The panel represented expertise in audiology, acoustics, otolaryngology, occupational/ environmental medicine, and public health. A se ries of conference calls were held among panel members to discuss literature and key heal th concerns that have been raised about wind turbines. The calls were followed by the development of a draft that was reviewed by other panel members. Throughout the follow-up period, literature was critically addressed.



# 2.2 Review of Literature Directly Related to Wind Turbines

The panel conducted a search of Pub Med un der the heading “Wind Turbines and Health Effects” to research and address peer-reviewed literature. In addition, the panel conducted a search on “vibroacoustic disease.” The refere nce section identifies the peer and non-peer reviewed sources that were consulted by the panel.



# 2.3 Review of Potential Environmental Exposures

The panel conducted a review of potential en vironmental exposures associated with wind turbine operations, with a focus on low fr equency sound, infrasound, and vibration.3-1 SECTION 3 

# Overview and Discussion

This section summarizes the results of the re view and analysis conducted by the expert panel and responds to a number of key questions:

• How do wind turbine operations affect human auditory response?

• How do we determine the loudness and frequency of sound and its effects on the human ear?

• How do wind turbines produce sound?

• How is sound measured and tested?

• What is vibration?

• W hat type of exposure to wind turbines is mo re likely to be perceived by humans (low frequency sound, infrasound or vibration)?

• Can sounds in the low frequency range, most notably the infrasonic range, adversely affect human health? Even when such levels are below the average person’s ability to hear them?

• How does the human vestibular system respond to sound?

• What are the potential adverse effects and health implications of sound exposure?

• What does scientific literature say abou t wind turbines, low frequency sound, and infrasound?



# 3.1 Wind Turbine Operation and Human Auditory Response to Sound

3.1.1 Overview The normal operation of a wind turbine prod uces sound and vibration, arousing concern about potential health implications. This se ction addresses the fundamental principles associated with sound and vibration, sound measurement, and potential adverse health implications. Sound from a wind turbine ar ises from its mechanical operation and the turning of the blades.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-2 

## 3.1.2 The Human Ear and Sound The human ear is capable of perceiving a wi de range of sounds, from the high-pitched sounds of a bird song to the low-pitched soun d of a bass guitar. Sounds are perceived based on their loudness (i.e., volume or sound pressu re level) or pitch (i.e., tonal or frequency content). The standard unit of measure for so und pressure levels is the decibel (dB). The standard unit used to describe the tonal or fr equency content is the Hertz (Hz), measured in cycles per second)—Appendix A provides more information on the fundamentals of sound. Customarily, the young, non-pathological ear can perceive sounds ranging from 20 Hz to 20,000 Hz. Appendix B provides more information on the human ear. Frequencies below 20 Hz are commonly called “infrasound,” although the boundary between infrasound and low frequency sound is not rigid. Infrasound, at certain frequencies and at high levels, can be audible to some people. Low frequency sound is customarily referred to as that between 10 Hz and 200 Hz, but any definition is arbitrary to some degree. Low frequency sound is the subject of concern to some with respect to potential health implications.

TABLE 3-1 TYPICAL SOUND PRESSURE LEVELS MEASURED IN THE ENVIRONMENT AND INDUSTRY
Noise Source At a Given Distance A-Weighted Sound Level in Decibels Qualitative Description
Carrier deck jet operation 140

130 Pain threshold Jet takeoff (200 feet) 120 Auto horn (3 feet) 110 Maximum vocal effort Jet takeoff (1000 feet) Shout (0.5 feet) 100

N.Y. subway station Heavy truck (50 feet) 90 Very annoying Hearing damage (8-hour,

continuous exposure) Pneumatic drill ( 50 feet) 80 Annoying Freight train (50 feet) Freeway traffic (50 feet) 70 to 80

70 Intrusive (Telephone use difficult) Air conditioning unit (20 feet) 60 Light auto traffic (50 feet) 50 Quiet Living room Bedroom 40

Library Soft whisper (5 feet) 30 Very quiet

Broadcasting/Recording studio 20

10 Just audible Adapted from Table E, “Assessing and Mitigati ng Noise Impacts”, NY DEC, February 2001.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-3 Table 3-1 shows sound pressure levels asso ciated with common activities. Typically, environmental and occupational sound pressure levels are measured in decibels on an A-weighted scale (dBA). The A-weighted scale de-emphasizes the very low and very high frequency components of the sound in a manne r similar to the frequency response of the human ear. For comparison, the sound from a wind turbine at distances between 1,000 and 2,000 feet is generally within 40 to 50 dBA. Section 3.2 discusses the effects of exposure to wind turbine sound. Section 3.3 describes the potential adverse effects of sound exposure as well as the health implications.



## 3.1.3 Sound Produced by Wind Turbines Wind turbine sound originates from either a mechanical or aerodynamic generation mechanism. Mechanical sound originates fr om the gearbox and control mechanisms. Standard noise control techniques typically are used to reduce mechanical sound. Mechanical noise is not typically the dominant so urce of noise from modern wind turbines (except for an occasional gear tone). The aerodynamic noise is present at all freque ncies, from the infrasound range over low frequency sound to the normal audible range and is the dominant source. The aerodynamic noise is generated by several mechanisms as is described below. The aerodynamic noise tends to be modulated in the mid frequency range, approximately 500 to 1,000 Hz. Aerodynamic sound is produced by the rotation of the turbine blades through the air. A turbine blade shape is that of an airfoil. An airfoil is simply a structure with a shape that produces a lift force when air passes over it . Originally developed for aircraft, airfoil shapes have been adapted to provide the turn ing force for wind turbines by employing a shape which causes the air to travel more rapi dly over the top of the airfoil than below it. The designs optimize efficiency by minimizing turbulence, wh ich produces drag and noise. An aerodynamically efficient blade is a quiet one. The aerodynamic sound from wind turbines is ca used by the interaction of the turbine blade with the turbulence produced both adjacent to it (turbulent boundary layer) and in its near wake (see Figure 3-1) (Brooks et al., 1989). Turbulence depends on how fast the blade is moving through the air. A 100-meter-diameter bl ade, rotating once every three seconds, has a tip velocity of just over 100 meters per se cond. However, the speed reduces at positions closer to the centre of rotation (the wind turbine hub). The main determinants of the turbulence are the speed of the blade and the shape and dimensions of its cross-section.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-4 FIGURE 3-1 Sound Produced by Wind Turbine Flow

The following conclusions have been derived from the flow conditions shown in Figure 3-1 (Brooks et al., 1989):

• At high velocities for a given blade, turbulen t boundary layers develop over much of the airfoil. Sound is produced when the turbul ent boundary layer passes over the trailing edge.

• At lower velocities, mainly laminar bounda ry layers develop, leading to vortex shedding at the trailing edge. Other factors in the production of ae rodynamic sound include the following:

• When the angle of attack is not zero—in othe r words, the blade is tilted into the wind— flow separation can occur on the suction side near to the trailing edge, producing sound.

• At high angles of attack, large-scale separation may occur in a stall condition, leading to radiation of low frequency sound.

• A blunt trailing edge leads to vort ex shedding and additional sound.

• The tip vortex contains highly turbulent flow. Each of the above factors may contribute to wind turbine sound prod uction. Measurements of the location of the sound source in wind turbines indicate that the dominant sound is produced along the blade—nearer to the tip en d than to the hub. Reduction of turbulence sound can be facilitated through airfoil shap e and by good maintenance. For example, surface irregularities resulting from damage or to accretion of additional material, may increase the sound.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-5 Aerodynamic sound has been shown to be generated at higher levels during the downward motion of the blade (i.e., the three o’clock posi tion). This results in a rise in level of approximately once per second for a typical three- bladed turbine. This periodic rise in level is also referred to as amplitude modulation , and as described above for a typical wind turbine, the modulation frequency is 1 Hz (onc e per second). In other words, the sound level rises and falls about once per second. The origin of this amplitude modulation is not fully understood. It was previously assumed that the modulation was caused when the blade went past the tower (given the tower disturbe d the airflow), but it is now thought to be related to the difference in wind speed between the top and bottom of the rotation of a blade and directivity of the aerodynamic noise (Oerlemans and Schepers, 2009). In other words, the result of aerodynamic mo dulation is a perceivable fluctuation in the sound level of approximately once per second . The frequency content of this fluctuating sound is typically between 500 Hz and 1,000 Hz, but can occur at higher and lower frequencies. That is, the sound pressure leve ls between approximately 500 and 1,000 Hz will rise and fall approximately once per second. It should be noted, however, that the magnitude of the amplitude modulation that is observed when standing beneath a tower does not always occur at greater separation distances. A study in the United Kingdom (UK) also showed that only four out of about 130 wind farms had a problem with aerodynamic modulation and three of these have b een solved (Moorhouse et al., 2007). In addition to the sound levels generated by the turbines, environmen tal factors affect the levels received at more distant locations. For example, warm air near the ground causes the turbine sound to curve upwards, away from the ground, which results in reduced sound levels, while warm air in a temperature invers ion may cause the sound to curve down to the earth resulting in increased sound levels. Wind may also cause the sound level to be greater downwind of the turbine—that is, if the wi nd is blowing from the source towards a receiver—or lower, if the wind is blowing fr om the receiver to the source. Most modeling techniques, when properly implemented, acco unt for moderate inversions and downwind conditions. Attenuation (reduction) of sound c an also be influenced by barriers, ground surface conditions, shrubbery and trees, among other things. Predictions of the sound level at varying dist ances from the turbine are based on turbine sound power levels. These turbine sound power levels are determined through standardized measurement methods.



## 3.1.4 Sound Measurement and Audiometric Testing

A sound level meter is a standard tool used in the measurement of sound pressure levels. As described in Section 3.1.2, the standard un it of sound pressure level (i.e., volume) is dB and the standard unit used to describe the pi tch or frequency is Hz (cycles per second). A sound level meter may use the A-weighting filter to adjust certain frequency ranges (those that humans detect poorly), resulting in a re ading in dBA (decibels, A-weighted). Appendix C provides more information on the measur ement of sound. The pitch or frequencies (sometimes referred to as sound level spectrum ) can be quantified using a sound level meter that includes a frequency analyzer. Octave ba nd, one-third octave band, and narrow band (such as Fast Fourier Transform, or FFT) are three common types of frequency analyzers.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-6 Consider, for example, a routine audiometric test (hearing test) in which a person sits in a booth and wears headphones, through which so unds are transmitted to evaluate hearing. Outside the booth, a technician turns a dial wh ich yields certain frequencies (for example, 125 Hz, a low-pitched sound, or 4,000 Hz, a high-pitched sound) and then the technician raises the volume of each frequency until the pe rson recognizes the sound of each tone. This is a standard approach used to measure th resholds for many reasons, including noiseinduced hearing loss (NIHL). As the technici an raises the volume of the designated frequency, the sound level (in dB) is noted. People who need more than 25 dB at more than one frequency to hear the sound (ie loudne ss of the tone) are considered to have an abnormal test. The effects of prolonged, high-level sound exposure on hearing have been determined through audiometric tests of workers in ce rtain occupations. The studies have been published in major medical journals and subjec ted to the peer review process (see, for example, McCunney and Meyer, 2007). Studies of workers have also served as the scientific basis for regulations on noise in industry that are overseen by the Occupational Safety and Health Administration (OSHA). Workers in nois e-intensive industries have been evaluated for NIHL and certain industries are known to be associated with high noise levels, such as aviation, construction, and areas of manufa cturing such as canning. Multiyear worker studies suggest that prolonged exposure to high noise levels can adversely affect hearing. The levels considered sufficiently high to ca use hearing loss are considerably higher than one could experience in the vicinity of wind turbines. For example, prolonged, unprotected high exposure to noise at levels greater than 90 dBA is a risk for hearing loss in occupational settings such that OSHA established this leve l for hearing protection. Sound levels from wind turbines do not approach these levels ( 50 dBA at a distance of 1,500 feet would be a conservative estimate for today’s turbines). Although the issue of NIHL has rarely been raised in opposition to wind farms, it is import ant to note that the risk of NIHL is directly dependent on the intensity (sound level) and du ration of noise exposure and therefore it is reasonable to conclude that there is no risk of NIHL from wind turbine sound. Such a conclusion is based on studies of workers ex posed to noise and among whom risk of NIHL is not apparent at levels less than 75 dBA.



# 3.2 Sound Exposure from Wind Turbine Operation

This section addresses the questions of (1) whether sounds in the low frequency range, most notably the infrasonic range, adversely affect human health, and whether they do so even when such levels are below the average pers on’s ability to hear them; (2) what we are referring to when we talk about vibration; and (3) how the human vestibular system responds to sound and disturbance. 

## 3.2.1 Infrasound and Low-Frequency Sound Infrasound and low frequency sound are addre ssed in some detail to offer perspective on publicized hypotheses that sound from a wind turbine may damage health even if the noise levels are below those associated with noise- induced hearing loss in industry. For example, it has been proposed that sounds that contai n low frequency noise, most notably within the infrasonic level, can adversely affect health even when the levels are below the average person’s ability to detect or hear th em (Alves-Pereira and Branco, 2007b).WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-7 Comprehensive reviews of infrasound and its sources and measurement have been published (Berglund and Lindvall, 1995; Leventhall et al., 2003). Table 3-2 shows the sound pressure level, in decibels, of the correspond ing frequency of infrasound and low frequency sound necessary for the sound to be heard by the average person (Leventhall et al., 2003).

TABLE 3-2 Hearing Thresholds in the Infrasonic and Low Frequency Range Frequency (Hz) 4 8 10 16 20 25 40 50 80 100 125 160 200
Sound pressure level (dB) 107 100 97 88 79 69 51 44 32 27 22 18 14

NOTE: Average hearing thresholds (for young healthy people) in the infrasound (4 to 20 Hz) and low frequency region (10 to 200 Hz). Source: Leventhall et al., 2003

As Table 3-2 indicates, at low frequencies, a much higher level sound is necessary for a sound to be heard in comparison to higher frequencies. For example, at 10 Hz, the sound must be at 97 dB to be audible. If this level occurred at the mid to high frequencies, which the ear detects effectively, it would be ro ughly equivalent to standing without hearing protection directly next to a power saw. Deci bel for decibel, the low frequencies are much more difficult to detect than the high frequenc ies, as shown in the hearing threshold levels of Table 3-2.

Table 3-2 also shows that even sounds as low as 4 Hz can be heard if the levels are high enough (107 dB). However, levels from wind tu rbines at 4 Hz are more likely to be around 70 dB or lower, and therefore inaudible. Stud ies conducted to assess wind turbine noise have shown that wind turbine sound at typical distances does not exceed the hearing threshold and will not be audible below abou t 50 Hz (Hayes 2006b; Kamperman and James, 2008). The hearing threshold level at 50 Hz is 44 dB, as shown in Table 3-2. Recent work on evaluating a large number of noise sources be tween 10 Hz and 160 Hz suggests that wind turbine noise heard indoors at typical separati on distances is modest on the scale of low frequency sound sources (Pedersen, 2008). The lo w levels of infrasound and low frequency sound from wind turbine operations have been confirmed by others (Jakobsen, 2004; van den Berg, 2004). The low frequency sound associated with wind turbines has attracted attention recently since the A-weighting scale that is used fo r occupational and environmental regulatory compliance does not work well with soun ds that have prominently low frequency components. Most environmental low frequenc y sound problems are caused by discrete tones (pitch or tones that are significantly higher in level (volume) than the neighboring frequencies); from, for example, an engine or compressor, not by continuous broadband sound. The high frequency sounds are assesse d by the A-weighted measurement and, given their shorter wavelengths, are controlled mo re readily. Low frequency sounds may be irritating to some people and, in fact, some low frequency sound complaints prove impossible to resolve (Leventhall et al., 2003). This observation leads to a perception that there is something special, sinister, and harmful about low frequency sound. To the contrary, most external sound when heard indo ors is biased towards low frequencies due to the efficient building attenuatio n of higher frequencies. One may recognize this when noiseWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-8 from a neighbor’s stereo is heard within th eir home—the bass notes are more pronounced than the higher frequency sounds. Any unwanted sound, whether high frequency or low frequency, can be irritating and stressful to some people. Differences in how a low frequency sound and high frequency sound are perceived are well documented. Figure 3-2 shows that lower-freque ncy sounds typically need to be at a high sound pressure level (dB) to be heard. Figure 3-2 also demonstrates that as the frequency lowers, the audible range is compressed leading to a more rapid rise in loudness as the level changes in the lower frequencies. At 1,000 Hz, the whole range covers about 100 dB change in sound pressure level, while at 20 Hz the same range of loudness covers about 50 dB (note the contours displayed in Figure 3-2 are in te rms of phons, a measure of equal loudness; for additional explanation on phons, the reader is referred to http://www.sfu.ca/sonicstudio/handbook/Phon.html [Truax, 1999]). As the annoyance of a given sound increases as loudness increases, there is also a more ra pid growth of annoyance at low frequencies. However, there is no evidence for direct physio logical effects from either infrasound or low frequency sound at the levels generated from wi nd turbines, indoors or outside. Effects may result from the sounds being audible, but thes e are similar to the effects from other audible sounds. Low frequency sound and infrasound are furt her addressed in Section 3.3, Potential Adverse Effects of Exposure to Sound.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-9 FIGURE 3-2 Hearing Contours for Equal Loudness Level (I nternational Standards Organization, 2003)



## 3.2.2 Vibration
Vibration, assumed to result from inaudible low frequency so unds, has been postulated to have a potential adverse effect on health. This section defines vibration, describes how it is measured, and cites studies that have addr essed the risk of vibration on health. Vibration refers to the way in which energy travels through solid material, whether steel, concrete in a bridge, the earth, the wall of a house or the human body. Vibration is distinguished from sound, which is energy flow ing through gases (like air) or liquids (like water). As higher frequency vibrations attenuate rapidly, it is low fr equencies which are of potential concern to human health. When vibration is de tected through the feet or through the seat, the focus of interest is the vibration of th e surface with which one is in contact—for example, when travelling in a vehicle. Vibration is often measured by the acceleration of the surface in meters per second, squared (m/s 2 ), although other related units are used. Vi bration can also be expressed in decibels, where the reference excitation leve l used in buildings is often 10 –5 m/s 2 and the vibration level is 20log (A/10 -5 ) dB, where A is the acceleration level in m/s 2

. The threshold of perception of vibratio n by humans is approximately 0.01 m/s 2 . If a frequency of excitation (vibration) corresponds with a resonant frequency of a system, thenWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-10 excitation at the resonant frequency is greater than at other frequencies. However, excitation by sound is not the same as excitation by mechanical excitation applied at, say, the feet. Figure 3-3 shows an object excited by point mechanical vibration and by sound. The object contains a resiliently suspended system. For example, if the object was the body, the suspended system might be the viscera (internal organs of th e body). The left hand of the figure can be interpreted as the body vibrated by input to the feet. The vibration of the viscera will be maximum at the resonant frequency 1 of the suspended system, which, for viscera, is about 4 Hz. When excitation is by long wavelength low frequency sound waves, as shown at the right of the figure, not only is the force acting on the body much smaller than for vibration input, but, as the wavelength is much greater than the dimensions of the body, it is acting around the body in a comp ressive manner so that there is no resultant force on the suspended system and it does not vibrate or resonate.

FIGURE 3-3 Comparison of Excitation of an Object by Vibration and by Sound

Unfortunately, this lack of effect has not b een addressed by those who have suggested the mechanical vibration response of the body instea d of the acoustic response as a potential health consequence. This oversight has led to inaccurate conclusions. For example, Dr. Nina Pierpont bases one of her key hypotheses for the cause of “wind turbine syndrome” on such an egregious error (Pierpont, 2009, pre-publ ication draft). Although not a recognized medical diagnosis, “wind turbine syndrome” ha s been raised as a concern for proposed projects—refer to Section 4.3 for more information. Vibration of the body by sound at one of its resonant frequencies occurs only at very high sound levels and is not a factor in the percepti on of wind turbine noise. As will be discussed

1 A common example of resonance is pushing a child on a swing in which energy is given to the swing to maximize its

oscillation.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-11 below, the sound levels associated with wind tu rbines do not affect the vestibular or other balance systems.



## 3.2.3 Vestibular System The vestibular system of the body plays a majo r role in maintaining a person’s sense of balance and the stabilization of visual images. The vestibular system responds to pressure changes (sound pressure, i.e., decibels) at variou s frequencies. At high levels of exposure to low frequency sound, nausea and changes in respiration and blood pressure may occur. Studies have shown, however, that for these effects to occur, considerably high noise levels (greater than 140 dB, similar in sound level of a jet aircraft heard 80 feet away) are necessary (Berglund et al., 1996). Head vibration resulting from low frequency so und has been suggested as a possible cause of a variety of symptoms that some hypothesize as being associated with wind turbines. In order to properly assess this hypothesis, this section addresses the human vestibular system. The “vestibular system” comprises the sense org ans in the vestibular labyrinth, in which there are five tiny sensory organs: three semici rcular canals that detect head rotation and two chalk-crystal-studded organs called otoliths (literally “ear-stones”) that detect tilt and linear motion of the head. All five organs cont ain hair cells, like those in the cochlea, that convert motion into nerve impulses travelin g to the brain in the vestibular nerve. These organs evolved millions of years before the middle ear. Fish, for example, have no middle ear or cochlea but have a vestibular laby rinth nearly identical to ours (Baloh and Honrubia, 1979). The vestibular or gans are specialized for stimulation by head position and movement, not by airborne sound. Each vestibular organ is firmly attached to the skull, to enable them to respond to the slightest head movement. In contrast, the hair cells in the cochlea are not directly attached to the skull; they do not normally respond to head movement, but to movements of the inner ear fluids. The otolith organs help fish hear low frequenc y sounds; even in primates, these organs will respond to head vibration (i.e., bone-condu cted sound) at frequencies up to 500 Hz (Fernandez and Goldberg, 1976). These vibratory responses of the vestibular system can be elicited by airborne sounds, however, only when they are at a much higher level than normal hearing thresholds 2 (and much higher than levels associ ated with wind turbine exposure). Thus, they do not help us hear but appear to be vestiges of our evolutionary past.

The vestibular nerve sends information about he ad position and movement to centers in the brain that also receive input from the eyes and from stretch receptors in the neck, trunk, and

2

Young et al. (1977) found that neurons coming from the ve stibular labyrinth of monkeys responded to head vibration at frequencies of 200-400 Hz, and at levels as low as 70 to 80 dB below gravitational force. Ho wever, these neurons could not respond to airborne sound at the same frequencies until levels exce eded 76 dB sound pressure level (SPL), which is at least 40 dB higher than the normal threshold of human hearing in this frequency range. Human eye movements respond to 100 Hz head vibration at levels 15 dB below audibl e levels (Todd et al., 2008a). This does not mean that the vestibular labyrinth is more sensitive than the cochlea to air borne sound, because the impedance-matching function of the middle ear allows the cochlea to respond to sounds that are 50-60 dB less intens e than those necessary to c ause detectable head vibration. Indeed, the same authors (Todd et al., 2008b) found that for ai rborne sound, responses from the cochlea could always be elicited by sounds that were below the threshold for vestibul ar responses. Similarly, Welgam pola et al. (2003) found that thresholds for vestibular evoked myogeni c potential response (VEMP) were higher than hearing thresholds and stated: “the difference between hearing thresholds and VEMP thresholds is much greater for air conducted sounds than for bone vibration.” In other words, the vestigial vestibular response to sound is relatively sensitive to bone conduction, which involv es vibration of the whole head, and much less sensitive to air conduction.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-12 legs (these stretch receptors tell which muscle s are contracted and which joints are flexed, and provide the “proprioceptive” sense of the body’s position and orientation in space). The brain integrates vestibular, vi sual, and proprioceptive inputs into a comprehensive analysis of the position and movement of the head and body, essential for the sense of balance, avoidance of falls, and keeping the eyes focused on relevant targets, even during movement. Perception of the body’s position in space may al so rely in part on input from receptors in abdominal organs (which can shift back and fo rth as the body tilts) and from pressure receptors in large blood vessels (blood pools in the legs when standing, then shifts back to the trunk when lying down). These “somatic graviceptors” (Mittelstaedt, 1996) could be activated by whole-body movement and possibly by structure-borne vibration, or by the blast of a powerful near explosion, but, as desc ribed in Section 4.3.2, it is unlikely that intraabdominal and intra-thoracic or gans and blood vessels could detect airborne sound like that created by wind turbines. Trauma, toxins, age-related degeneration, and various ear diseases can cause disorders of the vestibular labyrinth. A labyrinth not func tioning properly can cause a person to feel unsteady or even to fall. Since the semicircul ar canals of the ear normally detect head rotation (such as shaking the head to indicate “no”), one of the consequences of a dysfunctional canal is that a person may feel a “spinning” sensation. This reaction is described as vertigo, from the Latin word to turn. In normal conversation, words like vertigo and dizziness can be used in ambiguous ways and thus make ca reful interpretation of potential health claims problematic. “Di zzy,” for example, may mean true vertigo or unsteadiness, both of which may be symptoms of inner ear disease. A person who describes being ”dizzy” may actually be experiencing lig ht-headedness, a fainting sensation, blurred vision, disorientation, or almost any other di fficult-to-describe sensation in the head. The word “dizziness” can represent different sensatio ns to each person, with a variety of causes. This can make the proper interpretation of re search studies in which dizziness is evaluated a challenge to interpret. Proper diagnostic testing to ev aluate dizziness can reduce erro rs in misclassifying disease. The vestibular labyrinth, for example, can be tested for postural stability. Information from the semicircular canals is fed to the eye muscle s to allow us to keep our eyes focused on a target; when the head moves; this “vestibulo -ocular reflex” is easily tested and can be impaired in vestibular disorders (Baloh and Honrubia, 1979).



# 3.3 Potential Adverse Effects of Exposure to Sound

Adverse effects of sound are directly depend ent on the sound level; higher frequency sounds present a greater risk of an adverse e ffect than lower levels (see Table 3-2). Speech interference, hearing loss, and task interference occur at high sound levels. Softer sounds may be annoying or cause sleep disturbanc e in some people. At normal separation distances, wind turbines do not produce sound at levels that cause speech interference, but some people may find these sounds to be annoying.



## 3.3.1 Speech Interference It is common knowledge that conversation can be difficult in a noisy restaurant; the louder the background noise, the louder we talk and the harder it is to communicate. AverageWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-13 levels of casual conversation at 1 meter (arm ’s length) are typically 50 to 60 dBA. People raise their voices—slightly and unconsciously at first—when ambient levels exceed 50 to 55 dBA, in order to keep speech levels slightly above background noise levels. Communication at arm’s length requires consci ous extra effort when levels exceed about 75 dBA. Above ambient levels of 80 to 85 dBA, people need to shout or get closer to converse (Pearsons et al., 1977; Webster, 1978). Levels below 45 dBA can be considered irrelevant with respect to speech interference.



## 3.3.2 Noise-Induced Hearing Loss Very brief and intense sounds (above 130 dBA , such as in explosions) can cause instant cochlear damage and permanent hearing loss, but most occupational NIHL results from prolonged exposure to high noise levels between 90 and 105 dBA (McCunney and Meyer 2007). Regulatory (OSHA, 1983) and advisory (N IOSH, 1998) authorities in the U.S. concur that risk of NIHL begins at about 85 dBA, fo r an 8-hour day, over a 40-year career. Levels below 75 dBA do not pose a risk of NIHL. Thus, the sound levels associated with wind turbine operations would not cause NIHL because they are not high enough.



## 3.3.3 Task Interference Suter (1991) reviewed the effects of noise on performance and behavior. Simple tasks may be unaffected even at levels well above 100 dB A, while more complex tasks can be disrupted by intermittent noise as low as 75 dBA. Sp eech sounds are usually more disruptive than nonspeech sounds. Levels below 70 dBA do not result in task interference.



## 3.3.4 Annoyance Annoyance as a possible “effect” of wind turbin e operations is discussed in detail in later sections of this report (Sections 3.4 and 4.1). In summary, annoyance is a subjective response that varies among people to many types of sounds. It is important to note that although annoyance may be a frustrating experience for people, it is not considered an adverse health effect or disease of any kind. Certain everyda y sounds, such as a dripping faucet—barely audible—can be annoying. Annoya nce cannot be predicted easily with a sound level meter. Noise from airports, road traffic, and othe r sources (including wind turbines) may annoy some people, and, as described in Section 4.1, the louder the noise, the more people may become annoyed.



## 3.3.5 Sleep Disturbance The U.S. Environmental Protection Agency (EPA) document titled Information on Levels of Environmental Noise Requisite to Protect Public H ealth and Welfare with an Adequate Margin of Safety (1974) recommends that indoor day-night-level (DNL) not exceed 45 dBA. DNL is a 24-hour average that gives 10 dB extra weight to sounds occurring between 10p.m. and 7 a.m., on the assumption that during these sleep hours, levels above 35 dBA indoors may be disruptive.



## 3.3.6 Other Adverse Health Effects of Sound At extremely high sound levels, such as thos e associated with expl osions, the resulting sound pressure can injure any air-containing organ: not only the middle ear (eardrumWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-14 perforations are common) but also the lungs and intestines (Sasser et al., 2006). At the other extreme, any sound that is chronically annoying , including very soft sounds, may, for some people, create chronic stress, which can in turn lead to other health problems. On the other hand, many people become accustomed to regu lar exposure to noise or other potential stressors, and are no longer annoyed. The hypothesis that chronic noise exposure might lead to chronic health problems such as hypertensi on and heart disease has been the subject of hundreds of contradictory studies of highly va riable quality, which will not be reviewed in this document. Other authors have reviewed this literature, and some of their conclusions are quoted below: “It appears not likely that noise in industry can be a direct cause of general health problems..., except that the noise can create conditions of psychological stress...which can in turn cause physiological stress reactions...” (Kryter, 1980) “Epidemiological evidence on noise expo sure, blood pressure, and ischemic heart disease is still limited.” (Babisch, 2004), and “c ontradictory’ (Babisch, 1998), but “there is some evidence...of an increased risk in subj ects who live in noisy areas with outdoor noise levels of greater than 65 - 70 dBA.” (Babisch, 2000) “The present state of the art does not permit any definite conclusion to be drawn about the risk of hypertension.” (van Dijk, Ettema, and Zielhuis, 1987) “At this point, the relationship between noise induced hearing loss and hypertension must be considered as possible but lack ing sufficient evidence to draw causal associations." (McCunney and Meyer, 2007)



## 3.3.7 Potential Health Effects of Vibration Exposure People may experience vibration when some part of the body is in direct contact with a vibrating object. One example would be hold ing a chainsaw or pneumatic hammer in the hands. Another would be sitting in a bus, truck, or on heavy equipment such as a bulldozer. Chronic use of vibrating tools can cause “hand-arm vibration syndrome,” a vascular insufficiency condition characterized by nu mbness and tingling of the fingers, cold intolerance, “white-finger” attacks, and eventu ally even loss of fing ers due to inadequate blood supply. OSHA does not set limits for vi bration exposure, but the American National Standards Institute (ANSI) (2006) recommends that 8-hour workday exposures to hand-arm vibration (5 to 1400 Hz, summed over three orthogonal axes of movement) not exceed acceleration values of 2.5 m/s 2

. Excessive whole-body vibration is clearly linke d to low back pain (Wilder, Wasserman, and Wasserman, 2002) and may contribute to gastro intestinal and urinary disorders, although these associations are not well established. ANSI (1979) recommends 8-hour limits for whole-body vibration of 0.3 m/s 2 , for the body’s most sensitive frequency range of 4 to 8 Hz. This is about 30 times more intense than the weakest vibration that people can detect (0.01 m/s 2 ). Airborne sound can cause detectable body vibrat ion, but this occurs only at very high levels—usually above sound pressure levels of 100 dB (unweighted) (Smith, 2002; Takahashi et al., 2005; Yamada et al., 1983). There is no sc ientific evidence to suggest that modern wind turbines cause perceptible vibration in homes or that there is an associated health risk.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-15 

# 3.4 Peer-Reviewed Literature Focusing on Wind Turbines, Low-Frequency Sound, and Infrasound

This section addresses the scientific review of the literature that has evaluated wind turbines, the annoyance effect, low frequency sound, and infrasound.



## 3.4.1 Evaluation of Annoyance and Dose-Response Relationship of Wind Turbine Sound To date, three studies in Europe have specific ally evaluated potential health effects of people living in proximity to wind turbines (Pedersen and Persson Waye, 2004; Pedersen and Persson Waye, 2007; Pedersen et al., 2009). These studies have been primarily in Sweden and the Netherlands. Customarily, an e ligible group of people are selected for possible participation in the study based on thei r location with respect to a wind turbine. Control groups have not been included in any of these reports. In an article published in August 2009, investigat ors reported the results of their evaluation of 725 people in the Netherlands, who lived in th e vicinity of wind turb ines (Pedersen et al., 2009). The potential study population consiste d of approximately 70,000 people living within 2.5 kilometers of a wind turbine at sele cted sites in the Netherlands. The objective of the study was to (1) assess the relationship be tween wind turbine sound levels at dwellings and the probability of noise annoyance, taking into account possible moderating factors, and (2) explore the possibility of generalizing a do se response relationship for wind turbine noise by comparing the results of the st udy with previous studies in Sweden. Noise impact was quantified based on the rela tionship between the sound level (dose) and response with the latter measured as the prop ortion of people annoyed or highly annoyed by sound. Prior to this study, dose response curves had been modeled for wind turbines. Previous studies have noted different degrees of relationships between wind turbine sound levels and annoyance (Wolsink et al., 1993; Pedersen and Persson Waye, 2004; Pedersen and Persson Waye, 2007). Subjective responses were obtained through a survey. The calculation of the sound levels (dose) in Sweden and the Netherlands were similar. A dose response relationship was observed between calculated A-weighted soun d pressure levels and annoyance. Sounds from wind turbines were found to be more annoying than several other environmental sources at comparable sound levels. A strong correlation was also noted between noise annoyance and negative opinion of the impact of wind turbines on the landscape, a finding in earlier studies as well. The dominant qua lity of the sound was a swishing, the quality previously found to be the most annoying type. The authors concluded that this study could be used for calculating a dose response curve for wind turbine sound and annoyance. The st udy results suggest that wind turbine sound is easily perceived and, compared with sound from other sources, is annoying to a small percentage of people (5 percent at 35 to 40 dBA). In this study, the proportion of people who reported being annoyed by wind turbine noise was similar to merged data from two prev ious Swedish studies (Pederson and PerssonWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-16 Waye, 2004; Pedersen and Persson Waye, 2007). About 5 percent of respondents were annoyed at noise levels between 35 to 40 dBA and 18 percent at 40 to 45 dBA. Pedersen et al. also reported significant dose responses between wind turbine sound and self-reported annoyance (Pedersen and Persso n Waye, 2004). High exposed individuals responded more (78 percent) than low exposed individuals (60 percent) , which suggests that bias could have played a role in the final results. An analysis of two cross-sectional socio-ac oustic studies—one that addressed flat landscapes in mainly rural settings (Peder sen and Persson Waye, 2004) and another in different terrains (complex or flat) and different levels of urbanization (rural or suburban) (Pedersen and Persson Waye, 2007)—was pe rformed (Pedersen, 2008). Approximately 10 percent of over 1000 people surveyed via a questionnaire reported being very annoyed at sound levels of 40 dB and greater. Attitude towa rd the visual impact of the wind turbines had the same effect on annoyance. Response to wind turbine noise was significantly related to exposure expressed as A-weighted sound pressure levels dB. Among those who could hear wind turbine sound, annoyance with wind turbine noise was highly correlated to the sound characteristics: swishing, whistling, re sounding and pulsating/throbbing (Pedersen, 2008). A similar study in Sweden evaluated 754 people living near one of seven sites where wind turbine power was greater than 500 kilowatt (kW) (Pedersen and Persson Waye, 2007). Annoyance was correlated with sound level and also with negative attitude toward the visual impact of the wind turbines. Note that none of these studies included a control group. Earlier field studies performed among people livin g in the vicinity of wind turbines showed a correlation between sound pressure level and noise annoyance; however, annoyance was also influenced by visual factors and attitude s toward the impact of the wind turbines on the landscape. Noise annoyance was noted at lower sound pressure levels than annoyance from traffic noise. Although some people may be affected by annoyance, there is no scientific evidence that noise at levels create d by wind turbines could cause health problems (Pedersen and Högskolan, 2003).



## 3.4.2 Annoyance A feeling described as “annoyance” can be associ ated with acoustic factors such as wind turbine noise. There is considerable variabilit y, however, in how people become “annoyed” by environmental factors such as road cons truction and aviation noise, among others (Leventhall, 2004). Annoyance is clearly a subjec tive effect that will vary among people and circumstances. In extrem e cases, sleep disturbance may occur. Wind speed at the hub height of a wind turbine at night may be up to twic e as high as during the day and may lead to annoyance from the amplitude modulated sound of the wind turbine (van den Berg, 2003). However, in a study of 16 sites in 3 European countries, only a weak correlation was noted between sound pressure level and noise anno yance from wind turbines (Pedersen and Högskolan, 2003). In a detailed comparison of the role of noise sensitivity in response to environmental noise around international airports in Sydney, Lond on, and Amsterdam, it was shown that noise sensitivity increases one’s perception of annoyance independently of the level of noise exposure (van Kamp et al., 2004).WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

3-17 In a Swedish study, 84 out of 1,095 people li ving in the vicinity of a wind turbine in 12 geographical areas reported being fairly or very annoyed by wind turbines (Pedersen, 2008). It is important to note that no differences were reported among people who were “annoyed” in contrast to those who were not annoyed with respect to hearing impairment, diabetes, or cardiovascular disease. An earlie r study in Sweden showed that the proportion of people “annoyed” by wind turbine sound is higher than for other sources of environmental noise at the same decibel level (Pedersen and Persson Waye, 2004).



## 3.4.3 Low-Frequency Sound and Infrasound No scientific studies have specifically eval uated health effects from exposure to low frequency sound from wind turbines. Natura l sources of low frequency sound include wind, rivers, and waterfalls in both audibl e and non-audible frequencies. Other sources include road traffic, aircraft, and industri al machinery. The most common source of infrasound is vehicular (National Toxicology Program, 2001). Infrasound at a frequency of 20 Hz (the upper li mit of infrasound) is not detectable at levels lower than than 79 dB (Leventhall et al., 2003). Infrasound at 145 dB at 20 Hz and at 165 dB at 2 Hz can stimulate the auditory system and cause severe pain (Leventhall, 2006).These noise levels are substantially higher than any noise generated by wind turbines. The U.S. Food and Drug Administration (FDA) has appr oved the use of infrasound for therapeutic massage at 70 dB in the 8 to 14 Hz range (National Toxicology Program, 2001). In light of the FDA approval for this type of therapeutic use of infrasound, it is reasonable to conclude that exposure to infrasound in the 70 dB range is safe. According to a report of the National Research Council (NRC), low frequency sound is a concern for older wind turbines but not the modern type (National Research Council, 2007).4-1 SECTION 4 

# Results

This section discusses the results of the anaylsis presented in Section 3. Potential effects from infrasound, low frequency sound, and the fl uctuating aerodynamic “swish” from turbine blades are examined. Proposed hypotheses be tween wind turbine sound and physiological effects in the form of vibroacoustic diseas e, “wind turbine syndrome,” and visceral vibratory vestibular dist urbance are discussed.



# 4.1 Infrasound, Low-Frequency Sound, and Annoyance

Sound levels from wind turbines pose no ri sk of hearing loss or any other nonauditory effect. In fact, a recent review concluded t hat “Occupational noise-induced hearing damage does not occur below levels of 85 dBA.” (Ising and Kruppa, 2004) The levels of sound associated with wind turbine operations ar e considerably lower than industry levels associated with noise induced hearing loss. However, some people attribute certain health problems to wind turbine exposure. To make sense of these assertions, one must consider no t only the sound but the complex factors that may lead to the perception of “annoyance.” Most health complaints regarding wind turbines have centered on sound as the cause. There are two types of sounds from wind turbines: mechanical sound, which originates from the gearbox and control mechanisms, and the more dominant aerodynamical sound, which is present at all frequencies from the infrasound range over low frequency so und to the normal audible range. Infrasound from natural sources (for example, ocean waves and wind) surrounds us and is below the audible threshold. The infrasound emitte d from wind turbines is at a level of 50 to 70 dB, sometimes higher, but well below the audi ble threshold. There is a consensus among acoustic experts that the infrasound from wind turbines is of no consequence to health. One particular problem with many of these assertions about infrasound is that is that the term is often misused when the concerning sound is ac tually low frequency sound, not infrasound. Under many conditions, low frequency sound below about 40 Hz cannot be distinguished from environmental background sound from th e wind itself. Perceptible (meaning above both the background sound and the hearin g threshold), low frequency sound can be produced by wind turbines under conditions of unusually turbulent wind conditions, but the actual sound level depends on the distance of the listener from the turbine, as the sound attenuates (falls off) with distance. The hi gher the frequency, the greater the sound attenuates with distance—Appendix D provides more information on the propagation of sound. The low frequency sound emitted by spinning wind turbines could possibly be annoying to some when winds are unusually turb ulent, but there is no evidence that this level of sound could be harmful to health. If so, city dwelling would be impossible due to the similar levels of ambient sound levels normally present in urban environments. Nevertheless, a small number of people find city sound levels stressful.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-2 It is not usually the low frequency nonfluctuating sound component, however, that provokes complaints about wind turbine soun d. The fluctuating aerodynamic sound (swish) in the 500 to 1,000 Hz range occurs from th e wind turbine blades disturbing the air, modulated as the blades rotate which changes the sound dispersion characteristics in an audible manner. This fluctuating aerodynamic so und is the cause of most sound complaints regarding wind turbines, as it is harder to be come accustomed to fluctuating sound than to sound that does not fluctuate. However, this fluctuation does not always occur and a UK study showed that it had been a problem in only four out of 130 UK wind farms, and had been resolved in three of those (Moorhouse et al., 2007).



## 4.1.1 Infrasound and Low-Frequency Sound Infrasound occurs at frequencies less than 20 Hz. At low and inaudible levels, infrasound has been suggested as a cause of “wind tu rbine syndrome” and vibroacoustic disease (VAD)—refer to Section 4.2.1 for more informat ion on VAD. For infrasound to be heard, high sound levels are necessary (see Section 3, Table 3-2). There is little risk of short term acute exposure to high levels of infrasound . In experiments related to the Apollo space program, subjects were exposed to between 120 and 140 dB without known harmful effects. High level infrasound is less harmful than the same high levels of sound in the normal audible frequency range. High levels of low frequency sound can exci te body vibrations (Leventhall, 2003). Early attention to low frequency sound was directed to the U.S. space program, studies from which suggested that 24-hour exposures to 120 to 130 dB are tolerable below 20 Hz, the upper limit of infrasound. Modern wind turb ines produce sound that is assessed as infrasound at typical levels of 50 to 70 dB, be low the hearing threshold at those frequencies (Jakobsen, 2004). Jakobsen concluded that infras ound from wind turbines does not present a health concern. Fluctuations of wind turbin e sound, most notably the swish-swish sounds, are in the frequency range of 500 to 1,000 Hz, which is neither low frequency sound nor infrasound. The predominant sound from wind turbines, however, is often mischaracterized as infrasound and low frequency sound. Leve ls of infrasound near modern-scale wind farms are in general not perceptible to people. In the human body, the beat of the heart is at 1 to 2 Hz. Higher-frequency heart sounds measured externally to the body are in the low frequency range (27 to 35 dB at 20 to 40 Hz), al though the strongest frequency is that of the heartbeat (Sakai, Feigen, and Luisada, 1971). Lu ng sounds, measured externally to the body are in the range of 5 to 35 dB at 150 to 600 Hz (Fiz et al., 2008). Schust (2004) has given a comprehensive review of the effects of high level low frequency sound, up to 100 Hz.



## 4.1.2 Annoyance Annoyance is a broad topic on which volumes have been written. Annoyance can be caused by constant amplitude and amplitude modulated sounds containing rumble (Bradley, 1994). As the level of sound rises, an increasing number of those who hear it may become distressed, until eventually nearly everybody is affected, although to different degrees. This is a clear and easily understood process. Howeve r, what is not so clearly understood is that when the level of the sound reduces, so that ve ry few people are troubled by it, there remain a small number who may be adversely affected. This occurs at all frequencies, although there seems to be more subjective variability at the lower frequencies. The effect of lowWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-3 frequency sound on annoyance has recently b een reviewed (Leventhall, 2004). The standard deviation of the hearing threshold is approx imately 6 dB at low frequencies (Kurakata and Mizunami, 2008), so that about 2.5 percent of the population will have 12 dB more sensitive hearing than the average person. However, hear ing sensitivity alone does not appear to be the deciding factor with respect to annoyanc e. For example, the same type of sound may elicit different reactions among people: one pers on might say “Yes, I can hear the sound, but it does not bother me,” while another may say, “The sound is impossible, it is ruining my life.” There is no evidence of harmful effect s from the low levels of sound from wind turbines, as experienced by people in their homes. Studies have shown that peoples’ attitudes toward wind turbines may affect the level of annoyance that they report (Pedersen et al., 2009). Some authors emphasize the psychological effe cts of sounds (Kalveram, 2000; Kalveram et al., 1999). In an evaluation of 25 people expose d to five different wind turbine sounds at 40 dB, ratings of “annoyance” were different among different types of wind turbine noise (Persson Waye and Öhrström, 2002).
None of the psycho-acoustic parameters could explain the difference in annoyance responses. Another study of more than 2,000 people suggested that personality traits play a role in the perception of annoyance to enviro nmental issues such as sound (Persson et al., 2007). Annoyance originates from acoustical signals that are no t compatible with, or that disturb, psychological functions, in particular, disturbance of current ac tivities. Kalveram et al. (1999) suggest that the main function of noise annoyance is as a warning that fitness may be affected but that it causes little or no ph ysiological effect. Protracted annoyance, however, may undermine coping and progress to stress relate d effects. It appears that this is the main mechanism for effects on the health of a small number of people from prolonged exposure to low levels of noise. The main health effect of noise stress is disturbed sleep, which may lead to other consequences. Work with low frequencies has shown that an audible low frequency sound does not normally become objectionable unt il it is 10 to 15 dB above hearing threshold (Inukai et al., 2000; Yamada, 1980). An except ion is when a listener has developed hostility to the noise source, so that annoyance commences at a lower level.

There is no evidence that sound at the levels from wind turbines as heard in residences will cause direct physiological effects. A small nu mber of sensitive people, however, may be stressed by the sound and suffer sleep disturbances.



## 4.1.3 Other Aspects of Annoyance Some people have concluded that they have health problems caused directly by wind turbines. In order to make sense of these comp laints, we must consider not only the sound, but the complex factors culminating in annoyance. There is a large body of medical literature on stress and psychoacoustics. Three factors that may be pertinent to a short discussion of wind turbine annoyance effects are the nocebo effect, sensory integration dysfunc tion and somatoform disorders.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

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## 4.1.4 Nocebo Effect

The nocebo effect is an adverse outcome, a wors ening of mental or physical health, based on fear or belief in adverse effects. This is the opposite of the well known placebo effect, where belief in positive effects of an intervention may produce positive results (Spiegel, 1997). Several factors appear to be associated wi th the nocebo phenomenon: expectations of adverse effects; conditioning from prior expe riences; certain psychological characteristics such as anxiety, depression and the tendency to somatize (express psychological factors as physical symptoms; see below), and situational and contextual factors. A large range of reactions include hypervagotonia, manifested by idioventricular heart rhythm (a slow heart rate of 20 to 50 beats per minute resulting from an intrinsic pacemaker within the ventricles which takes over when normal sinoatrial node regulation is lost), drowsiness, nausea, fatigue, insomnia, headache, weakness, dizzine ss, gastrointestinal (GI) complaints and difficulty concentrating (Sadock and Sadock, 2005, p.2425). This array of symptoms is similar to the so-called “wind turbine syndrome ” coined by Pierpont (2009, pre-publication draft). Yet these are all common symptoms in the general population and no evidence has been presented that such symptoms are more common in persons living near wind turbines. Nevertheless, the large volume of media covera ge devoted to alleged adverse health effects of wind turbines understandably creates an anticipatory fear in some that they will experience adverse effects from wind turbines. Every person is suggestible to some degree. The resulting stress, fear, and hypervigilance ma y exacerbate or even create problems which would not otherwise exist. In this way, anti-w ind farm activists may be creating with their publicity some of the problems that they describe.


## 4.1.5 Somatoform Disorders

There are seven somatoform disord ers in the Fourth Edition of Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) (American Psyc hiatric Association, 2000). Somatoform disorders are physical symptoms wh ich reflect psychological states rather than arising from physical causes. One common soma toform disorder, Conversion Disorder, is the unconscious expression of stress and anx iety as one or more physical symptoms (Escobar and Canino, 1989). Co mmon conversion symptoms are sensations of tingling or discomfort, fatigue, poorly localized abdomi nal pain, headaches, back or neck pain, weakness, loss of balance, hearing and visual abnormalities. The symptoms are not feigned and must be present for at least six months according to DSM-IV-TR and two years according to the International Statistical Cla ssification of Diseases and Related Health Problems, 10th Revision (ICD-10) (WHO, 1993). ICD-10 specifies the symptoms as belonging to four groups: (1) Gastrointestinal (abdomi nal pain, nausea, bloating/gas/, bad taste in mouth/excessive tongue coating, vomiti ng/regurgitation, frequent/loose bowel movements); (2) Cardiovascular (breathl essness without exertion, chest pains); (3) Genitourinary (frequency or dysuria, unpleasant genital sensations, vaginal discharge), and (4) Skin and Pain (blotchiness or discolorat ion of the skin, pain in the limbs, extremities or joints, paresthesias). ICD-10 specifies that at least six symptoms must be present in two or more groups. One feature of somatoform disorders is somatosensory amplification , a process in which a person learns to feel body sensations more ac utely and may misinterpret the significance of those sensations by equating th em with illness (Barsky, 1979). Sensory integration dysfunctionWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-5 describes abnormal sensitivity to any or all sensory stimuli (sound, touch, light, smell, and taste). There is controversy among research ers and clinicians as to whether sensory integration problems exist as an independent entity or as components of a pervasive developmental disorder (Sadock and Sadock, 2005, p. 3135), but their presence can lead to overestimation of the likelihood of be ing ill (Sadock and Sadock, 2005, p. 1803). Sensory integration dysfunction as such is not lis ted in the DSM-IV-TR or in the ICD-10. Day-to-day stressors and adverse life events provide multiple stimuli to which people respond, and that response is often somatic due to catecholamines and activation of the autonomic nervous system. This stress response can become conditioned as memory. There is some evidence that poor coping mechanisms ( anger impulsivity, hostility, isolation, lack of confiding in others) are linked to physiolo gical reactivity, which is associated with somatic sensation and amplification (Sadock and Sadock, 2005, p. 1806). In summary, the similarities of common huma n stress responses and conversion symptoms to those described as “wind turbine syndrome ” are striking. An annoyance factor to wind turbine sounds undoubtedly exists, to which ther e is a great deal of individual variability. Stress has multiple causes and is additive. Associated stress from annoyance, exacerbated by the rhetoric, fears, and negative publicit y generated by the wind turbine controversy, may contribute to the reported symptoms descri bed by some people living near rural wind turbines.



# 4.2 Infrasound, Low-frequency Sound and Disease

Some reports have suggested a link between lo w frequency sound from wind turbines and certain adverse health effects. A careful review of these reports, however, leads a critical reviewer to question the validity of the claims for a number of reasons, most notably (1) the level of sound exposure associated with the putati ve health effects, (2) the lack of diagnostic specificity associated with the health effects re ported, and (3) the lack of a control group in the analysis.



## 4.2.1 Vibroacoustic Disease Vibroacoustic disease (VAD) in the context of exposure of aircraft engine technicians to sound was defined by Portuguese researchers as a whole-body, multi-system entity, caused by chronic exposure to large pressure amp litude and low frequency (LPALF) sound (AlvesPereira and Castelo Branco, 2007a; Alves-Pere ira and Castelo Branco, 2007b; Alves-Pereira and Castelo Branco, 2007c; Alves-Pereira and Castelo Branco, 2007d). VAD, the primary feature of which is thickening of cardiovasc ular structures, such as cardiac muscle and blood vessels, was first noted among airplane technicians, military pilots, and disc jockeys (Maschke, 2004; Castelo Branco, 1999). Workers had been exposed to high levels for more than 10 years. There are no epidemiological stud ies that have evaluated risk of VAD from exposure to infrasound. The likelihood of such a risk, however, is remote in light of the much lower vibration levels in the body itself. Studies of workers with substantially higher exposure levels have not indicated a risk of VAD. VAD has been described as leading from initial respiratory infections, through pericardial thickening to severe and life-threatening illness such as stroke, myocardial infarction , and risk of malignancy (Alves-Pereira and Castelo Branco, 2007a).WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

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## 4.2.2 High-Frequency Exposure All of the exposures of subjects for whom th e VAD concept was developed, were dominated by higher frequency sounds, a critical poin t since the frequency range claimed for VADinducing sound is much wider than the freque ncy range of exposures experienced by the aircraft technicians who were diagnosed wi th VAD (Castelo Branco, 1999). Originally, proponents of the VAD concept had proposed a “greater than 90 dB” criterion for VAD. However, now some claim that VAD will result from exposure to almost any level of infrasound and low frequency sound at any frequency below 500 Hz. This assertion is an extraordinary extrapolation given that the co ncept of VAD developed from observations that a technician, working around military airc raft on the ground, with engines operating, displayed disorientation (Castelo Branco, 1999). Sound levels near aircraft were very high. In an evaluation of typical en gine spectra of carrier based co mbat aircraft operating on the ground, the spectra peaked at frequencies above 100 Hz with sound levels from 120 to 135 dB close to the aircraft (Smith, 2002). The le vels drop considerably, however, into the low frequency region.

There is an enormous decibel difference between the sound exposure of aircraft technicians and the sound exposure of people who live near wind turbines. Animal experiments indicated that exposure levels necessary to cause VAD were 13 weeks of continuous exposure to approximately 100 dB of low frequency sound (Mendes et al., 2007). The exposure levels were at least 50 to 60 dB higher than wind turbine levels in the same frequency region (Hayes, 2006a).



## 4.2.3 Residential Exposure: A Case Series Extrapolation of results from sound levels gr eater than 90 dB and at predominantly higher frequencies (greater than 100 Hz) to a risk of VAD from inaudible wind turbine sound levels of 40 to 50 dB in the infrasound region, is a new hypothesis. One investigator, for example, has claimed that wind turbines in residentia l areas produce acoustical environments that can lead to the development of VAD in near by home-dwellers (Alves-Pereira and Castelo Branco, 2007a). This claim is based on comparison of only two infrasound exposures. The first is for a family which has experienced a range of health problems and which also complained of disturbances from low frequency sound. The se cond is for a family which lived near four wind turbines, about which they have become anxious (Alves-Pereira and Castelo Branco, 2007a; Alves-Pereira and Castelo Branco, 2007b). The first family (Family F), was exposed to low levels of infrasound consisting of about 50 dB at 8 Hz and 10 Hz from a grain terminal ab out 3 kilometers (km) away and additional sources of low frequency sound, including a nearer railway line and road. The second family (Family R) lives in a rural area and was described as exposed to infrasound levels of about 55 dB to 60 dB at 8 Hz to 16 Hz. These exposures are well below the hearing threshold and not uncommon in urban areas. Neither the frequency nor volume of the sound exposures experienced by Families F or R are unus ual. Exposure to infrasound (< 20 Hz) did not exceed 50 dB.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

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### 4.2.3.1 Family F—Exposure to Low Levels of Infrasound Family F has a long history of poor health and a 10-year-old boy was diagnosed with VAD due to exposure to infrasound from the grain terminal (Alv es-Pereira and Castelo Branco, 2007a; Castelo Branco et al., 2004). However, the infrasound levels are well below hearing threshold and are typical of urban infrasound , which occurs widely and to which many people are exposed. According to the authors, the main effect of VAD was demonstrated by the 10-year-old boy in the family, as pericardial thickening. 3 However, the boy has a history of poor health of unknown etiology (Castelo Branco et al., 2004). Castelo Branco (1999) has defined pericardial thickening as an indicator of VAD and assumes that the presence of pericardial thickening in the boy from Family F must be an effect of VAD, caused by exposure to the low-level, low frequency sound from the grai n terminal. This assumption excludes other possible causes of pericardial thickening, includ ing viral infection, tuberculosis, irradiation, hemodialysis, neoplasia with pericardial infiltrati on, bacterial, fungal, or parasitic infections, inflammation after myocardial infarction, asbe stosis, and autoimmune diseases. The authors did not exclude these other possible causes of pericardial thickening.



### 4.2.3.2 Family R—Proximity to Turbines and Anxiety Family R, living close to the wind turbines , has low frequency sound exposure similar to that of Family F. The family does not have symptoms of VAD, but it was claimed that “Family R. will also develop VAD should they choose to remain in their home.” (AlvesPereira and Castelo Branco, 2007b). In light of the absence of literature of cohort and case control studies, this bold statement seems to be unsubstantiated by available scientific literature.



## 4.2.4 Critique It appears that Families F and R were self-s elected complainants. Conclusions derived by Alves-Pereira and Castelo Branco (2007b) have been based only on the poor health and the sound exposure of Family F, using this single exposure as a measure of potential harmful effects for others. There has been no attempt at an epidemiological study.

Alves-Pereira and Castelo Branco claim that ex posure at home is more significant than exposure at work because of the longer peri ods of exposure (Alves -Pereira and Castelo Branco, 2007e). Because an approximate 50 dB di fference occurs between the exposure from wind turbines and the exposure that induced VAD (Hayes, 2006a), it will take 10 5 years (100,000 years) for the wind turbine dose to equal that of one year of the higher level sound. Among published scientific literature, this desc ription of the two families is known as a case series, which are of virtually no value in understanding potential causal associations between exposure to a potential hazard (i.e., low frequency sound) and a potential health effect (i.e., vibroacoustic disease). Case repo rts have value but primarily in generating hypotheses to test in other studies such as larg e groups of people or in case control studies. The latter type of study can systematically eval uate people with pericardial thickening who live near wind turbines in comparison to peop le with pericardial thickening who do not live

3 Pericardial thickening is unusual thickeni ng of the protective sac (pericardium) wh ich surrounds the heart. For example, see

http://www.emedicine.com/radio/topic191.htm

.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-8 near wind turbines. Case reports need to be co nfirmed in larger studies, most notably cohort studies and case-control studies, before definiti ve cause and effect assertions can be drawn. The reports of the two families do not provid e persuasive scientific evidence of a link between wind turbine sound and pericardial thickening. Wind turbines produce low levels of infrasou nd and low frequency sound, yet there is no credible scientific evidence that these levels are harmful. If the human body is affected by low, sub-threshold sound levels, a unique and not yet discovered receptor mechanism of extraordinary sensitivity to sound is ne cessary—a mechanism which can distinguish between the normal, relatively high-lev el “sound” inherent in the human body 4 and excitation by external, low-level sound. Esse ntial epidemiological studies of the potential effects of exposure at low sound levels at low frequencies have not been conducted. Until the fuzziness is clarified, and a receptor me chanism revealed, no reliance can be placed on the case reports that the low levels of infrasound and low frequency sound are a cause of vibroacoustic disease. 5 The attribution of dangerous properties to low levels of infrasound continues unproven, as it has been for the past 40 years. No fo undation has been demonstrated for the new hypothesis that exposure to sub-threshold, low levels of infrasound will lead to vibroacoustic disease. Indeed, human evolutio n has occurred in the presence of natural infrasound.



# 4.3 Wind Turbine Syndrome

“Wind turbine syndrome” as promoted by Pierpo nt (2009, pre-publication draft) appears to be based on the following two hypotheses:

1. Low levels of airborne infrasound from wind turbines, at 1 to 2 Hz, directly affect the vestibular system.

2. Low levels of airborne infrasound from wind turbines at 4 to 8 Hz enter the lungs via the mouth and then vibrate the diaphragm, which tran smits vibration to the viscera, or internal organs of the body.

The combined effect of these infrasound fr equencies sends confusing information to the position and motion detectors of the body, wh ich in turn leads to a range of disturbing symptoms.



## 4.3.1 Evaluation of Infrasound on the Vestibular System Consider the first hypothesis. The support fo r this hypothesis is a report apparently misunderstood to mean that the vestibular syst em is more sensitive than the cochlea to low levels of both sound and vibration (Todd et al., 2008a). The Todd report is concerned with vibration input to the mastoid area of the sk ull, and the corresponding detection of these vibrations by the cochlea and vestibular system. The lowest frequency used was 100 Hz,

4 Body sounds are often used for diagnosis. For example see Gross, V., A. Dittmar , T. Penzel, F., Schüttler, and P. von

Wichert.. (2000): "The Relationship between Normal Lung Sounds, Age, and Gender. " American Journal of Respiratory and Critical Care Medicine . Volume 162, Number 3: 905 - 909. 5 This statement should not be interpreted as a criticism of t he work of the VAD Group with ai rcraft technicians at high noise

levels.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-9 considerably higher than the upper limit of the infrasound frequency (20 Hz). The report does not address air-conducted sound or infr asound, which according to Pierpont excites the vestibular system by airborne sound and by skull vibration. This source does not support Pierpont’s hypothesis and does not demonstrate the points that she is trying to make.

There is no credible scientific evidence that low levels of wind turbine sound at 1 to 2 Hz will directly affect the vestibular system. In fact , it is likely that the sound will be lost in the natural infrasonic background sound of th e body. The second hypothesis is equally unsupported with appropriate scientific invest igations. The body is a noisy system at low frequencies. In addition to the beating heart at a frequency of 1 to 2 Hz, the body emits sounds from blood circulation, bowels, stomac h, muscle contraction, and other internal sources. Body sounds can be detected externally to the body by the stethoscope.



## 4.3.2 Evaluation of Infrasound on Internal organs It is well known that one source of sound may mask the effect of another similar source. If an external sound is detected within the bo dy in the presence of internally generated sounds, the external sound must produce a gr eater effect in the body than the internal sounds. The skin is very reflecti ve at higher frequencies, althou gh the reflectivity reduces at lower frequencies (Katz, 2000). Investigations at very low frequencies show a reduction of about 30 dB from external to internal sound in the body of a sheep (Peters et al., 1993). These results suggest an attenuation (reduction) of low frequency sound by the body before the low frequency sound reaches the internal organs. Low-level sounds from outside the body do not cause a high enough excitation within the body to exceed the internal body sounds. Pier pont refers to papers from Takahashi and colleagues on vibration excitation of the head by high levels of external sound (over 100 dB). However, these papers state that response of the head at frequencies below 20 Hz was not measurable due to the masking effect of inte rnal body vibration (Takahashi et al., 2005; Takahashi et al., 1999). When measuring chest re sonant vibration caused by external sounds, the internal vibration masks resonance for ex ternal sounds below 80 dB excitation level (Leventhall, 2006). Thus, the second hypothesis also fails. To recruit subjects for her study, Pierpont se nt out a general call for anybody believing their health had been adversely affected by wind turbines. She asked respondents to contact her for a telephone interview. The case series resu lts for ten families (37 subjects) are presented in Pierpont (2009, pre-publication draft). Sy mptoms included sleep disturbance, headache, tinnitus, ear pressure, vertigo, nausea, vi sual blurring, tachycardia, irritability, concentration, memory, panic attacks, internal pulsation, and quivering. This type of study is known as a case series. A case series is of limited, if any, value in evaluating causal connections between an environmental exposure (in this case, sound) and a designated health effect (so called “wind turbine syndrome”). This particular case series is substantially limited by selection bias, in which people who al ready think that they have been affected by wind turbines “self select“ to participate in the case series. This approach introduces a significant bias in the results, especially in the absence of a control group who do not live in proximity of a wind turbine. The results of this case series are at best hypothesis-generating activities that do not provide support for a causal link between wind turbine sound and socalled “wind turbine syndrome.”WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-10 However, these so called “wind turbine syndrome“ symptoms are not new and have been published previously in the context of “annoyanc e” to environmental sounds (Nagai et al., 1989; Møller and Lydolf, 2002; Mirowska and Mroz, 2000). The following symptoms are based on the experience of noise sufferers exte nding over a number of years: distraction, dizziness, eye strain, fatigue, feeling vibratio n, headache, insomnia, muscle spasm, nausea, nose bleeds, palpitations, pressure in the ears or head, skin burns, stress, and tension (Leventhall, 2002). The symptoms are common in cases of extreme and persistent annoyance, leading to stress responses in the affected individual and may also result from severe tinnitus, when there is no external sound. The sympto ms are exhibited by a small proportion of sensitive persons and may be alleviated by a course of psycho therapy, aimed at desensitization from the sound (Leventhall et al., 2008). The similarity between the symptoms of noise annoyance and those of “wind turbine syndrome” indicates that this “diagnosis“ is not a pathophysiological effect, but is an example of the well-known stress effects of exposure to noise, as displayed by a small proportion of the population. These effects are familiar to environmental noise control officers and other “on the ground” professionals. “Wind turbine syndrome,” not a recognized medi cal diagnosis, is essentially reflective of symptoms associated with noise annoyance and is an unnecessary and confusing addition to the vocabulary on noise. This syndrome is not a recognized diagnosis in the medical community. There are no unique symptoms or combinations of symptoms that would lead to a specific pattern of this hypothesized disorder. The collective symptoms in some people exposed to wind turbines are more likely asso ciated with annoyance to low sound levels.



# 4.4 Visceral Vibratory Vestibular Disturbance

4.4.1 Hypothesis In addition to case reports of symptoms repo rted by people who live near wind turbines, Pierpont has proposed a hypothesis that purp orts to explain how some of these symptoms arise: visceral vibratory ve stibular disturbance (VVVD) (P ierpont, 2009, pre-publication draft). VVVD has been described as consisting of vibration associated with low frequencies that enters the body and causes a myriad of symptoms. Pierpont considers VVVD to be the most distinctive feature of a nonspecific set of symptoms that she describes as “wind turbine syndrome.” As the name VVVD implies, wind turb ine sound in the 4 to 8 Hz spectral region is hypothesized to cause vibrations in abdomi nal viscera (e.g., intestines, liver, and kidneys) that in turn send neural signals to the part of the brain that normally receives information from the vestibular labyrinth. These signals hypothetically conflict with signals from the vestibular labyrinth and other sensory inputs (v isual, proprioceptive), leading to unpleasant symptoms, including panic. Unpleasant symp toms (especially nausea) can certainly be caused by sensory conflict; this is how scient ists explain motion sickness. However, this hypothesis of VVVD is implausible based on knowledge of sensory systems and the energy needed to stimulate them. Whether implausibl e or not, there are time-tested scientific methods available to evaluate the legitimacy of any hypothesis and at this stage, VVVD as proposed by Pierpont is an untested hypothes is. A case series of 10 families recruited to participate in a study based on certain symptoms would not be considered evidence of causality by research or policy institutions such as the Inter national Agency for Research onWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-11 Cancer (IARC) or EPA. As noted earlier in this report, a case series of self-selected patients does not constitute evidence of a causal connection.



## 4.4.2 Critique Receptors capable of sensing vibration are loca ted predominantly in the skin and joints. A clinical neurological examination normally includ es assessment of vibration sensitivity. It is highly unlikely, however, that airborne soun d at comfortable levels could stimulate these receptors, because most of airborne soun d energy is reflected away from the body. Takahashi et al. (2005) used airborne sound to produce chest or abdominal vibration that exceeded ambient body levels. This vibration may or may not have been detectable by the subjects. Takahashi found that levels of 100 dB sound pressure level were required at 20 to 50 Hz (even higher levels would have been re quired at lower and higher frequencies). Sounds like this would be considered by most people to be very loud, and are well beyond the levels produced by wind turbines at resi dential distances. Comparison of the responses to low frequency airborne sound by normal hearing and profoundly deaf persons has shown that deaf subjects can detect sound transmitted through their body only when it is well above the normal hearing threshold (Yamada et al., 1983). For example, at 16 Hz, the deaf persons’ average threshold was 128 dB soun d pressure level, 40 dB higher than that of the hearing subjects. It has also been shown t hat, at higher frequencies, the body surface is very reflective of sound (Katz, 2000). Simila rly, work on transmission of low frequency sound into the bodies of sheep has shown a loss of about 30 dB (Peters et al., 1993) The visceral receptors invoked as a mechani sm for VVVD have been shown to respond to static gravitational position changes, but not to vibration (that is why they are called graviceptors). If there were vibration-sensit ive receptors in the abdominal viscera, they would be constantly barraged by low frequenc y body sounds such as pulsatile blood flow and bowel sounds, while external sounds would be attenuated by both the impedance mismatch and dissipation of energy in the over lying tissues. Finally, wind turbine sound at realistic distances possesses little, if any, acoustic energy, at 4 to 8 Hz. It has been hypothesized that the vestibular labyrinth may be “abnormally stimulated” by wind turbine sound (Pierpont, 2009, pre-publicat ion draft). As noted in earlier sections of this report, moderately loud airborne sound, at frequencies up to about 500 Hz, can indeed stimulate not only the cochlea (the hearing organ) but also the otolith organs. This is not abnormal, and there is no evidence in the medica l literature that it is in any way unpleasant or harmful. In ordinary life, most of us are exposed for hours every day to sounds louder than those experienced at realistic distances fr om wind turbines, with no adverse effects. This assertion that the vestibular labyrinth is stimulated at le vels below hearing threshold is based on a misunderstanding of research that used bone-conducted vibration rather than airborne sound. Indeed, those who wear bone conduction hearing aids experience constant stimulation of their vestibular systems, in addi tion to the cochlea, without adverse effects.



# 4.5 Interpreting Studies and Reports

In light of the unproven hypotheses that have been introduced as reflective of adverse health effects attributed to wind turbines, it c an be instructive to review the type of research studies that can be used to determine definiti ve links between exposure to an environmentalWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-12 hazard (in this case, sound and vibration emissi ons from wind turbines) and adverse health effects (the so-called “wind turbine syndrome”). How do we know, for example, that cigarettes cause lung cancer and that excessive noise causes hearing loss? Almost always, the first indication that an exposure might be harmful comes from the informal observations of doct ors who notice a possible correlation between an exposure and a disease, then communicate thei r findings to colleagues in case reports, or reports of groups of cases ( case series ). These initial observations are usually uncontrolled; that is, there is no comparison of the people who have both exposure and disease to control groups of people who are either non-exposed or disease-free. There is usually no way to be sure that the apparent association is statistically significant (as opposed to simple coincidence), or that there is a causal relati onship between the exposure and the disease in question, without control subjects. For these re asons, case reports and case series cannot prove that an exposure is really harmful, but can only help to develop hypotheses that can then be tested in controlled studies (Levine et al., 1994; Genovese, 2004; McLaughlin, 2003). Once suspicion of harm has been raised, cont rolled studies (case-control or cohort) are essential to determine whether or not a causal association is likely, and only after multiple independent-controlled studies show consistent results is the association likely to be broadly accepted (IARC, 2006).

Case-control studies compare people with the di sease to people without the disease (ensuring as far as possible that the two grou ps are well-matched with respect to all other variables that might affect the chance of having the disease, such as age, sex, and other exposures known to cause the dise ase). If the disease group is found to be much more likely to have had the exposure in question, and if multiple types of error and bias can be excluded (Genovese, 2004), a causal link is likely. Multiple case-control studies were necessary before the link between smoking and lung cancer could be proved.

Cohort studies compare people with the exposure to well-matched control subjects who have not had that exposure. If the exposed group proves to be much more likely to have the disease, assuming error and bias can be excl uded, a causal link is likely. After multiple cohort studies, it was clear that excessive noise exposure caused hearing loss (McCunney and Meyer, 2007).

In the case of wind turbine noise and its hypothetical relationships to “wind turbine syndrome” and vibroacoustic disease, the weakest type of evidence—case series—is available, from only a single investigator. These reports can do no more than suggest hypotheses for further research. Nevertheless, if additional and independent investigators begin to report adverse health effects in people exposed to wind turbine noise, in excess of those found in unexposed groups, and if some consistent syndrome or set of symptoms emerges, this advice could change. Thus, at this time, “wind turbine syndrome” and VVVD are unproven hypotheses (essentially unproven ideas) that have not been confirmed by appropriate research studies, most notably cohort and case control studies. However, the weakness of the basic hypotheses makes such studies unlikely to proceed.WIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

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# 4.6 Standards for Siting Wind Turbines

4.6.1 Introduction While the use of large industrial-scale wind turbines is well established in Europe, the development of comparable wind energy fac ilities in North America is a more recent occurrence. The growth of wind and other renewable energy sources is expected to continue. Opponents of wind energy development argue that the height and setback regulations established in some jurisdictions are too lenient and that the noise limits which are applied to other sources of noise (either in dustrial or transportat ion) are not sufficient for wind turbines for a variety of reasons. Ther efore, they are concerned that the health and well-being of some residents who live in the vici nity (or close proximity to) of these facilities is threatened. Critics maintain that wind tu rbine noise may present more than an annoyance to nearby residents especially at night when ambient levels may be low. Consequently, there are those who advocate for a revision of th e existing regulations for noise and setback pertaining to the siting of wind installations ( Kamperman and James, 2009 ) . Some have indicated their belief that setbacks of more t han 1 mile may be necessary. While the primary purpose of this study was to evaluate the po tential for adverse health effects rather than develop public policy, the panel does not fi nd that setbacks of 1 mile are warranted.



## 4.6.2 Noise Regulations and Ordinances In 1974, EPA published a report that examined the levels of environmental noise necessary to protect public health and we lfare (EPA, 1974). Based on the analysis of available scientific data, EPA specified a range of day-night sound le vels necessary to protect the public health and welfare from the effects of environmental noise, with a reasonable margin of safety. Rather than establishing standards or regula tions, however, EPA simply identified noise levels below which the general public would not be placed at risk from any of the identified effects of noise. Each federal agency has de veloped its own noise criteria for sources for which they have jurisdiction (i.e., the Federal Av iation Administration regulates aircraft and airport noise, the Federal Highway Administration regulates highway noise, and the Federal Energy Regulatory Commission regulates in terstate pipelines (Bastasch, 2005). State and local governments were provided guidance by EPA on how to develop their own noise regulations, but the establishment of appropri ate limits was left to local authorities to determine given each community’s differing va lues and land use priorities (EPA, 1975).



## 4.6.3 Wind Turbine Siting Guidelines Establishing appropriate noise limits and setb ack distances for wind turbines has been a concern of many who are interested in wind energy. There are several approaches to regulating noise, from any source, including wi nd turbines. They can generally be classified as absolute or relative standards or a comb ination of absolute and relative standards. Absolute standards establish a fixed limit irre spective of existing noise levels. For wind turbines, a single absolute limit may be esta blished regardless of wind speed (i.e., 50 dBA) or different limits may be established for variou s wind speeds (i.e., 40 dBA at 5 meters per second [m/s] and 45 dBA at 8 m/s). The Ontario Ministry of Environment (2008) wind turbine noise guidelines is an example of fixed limits for each integer wind speed between 4 and 10 meters per second. Relative standards li mit the increase over existing levels and mayWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-14 also establish either an absolu te floor or ceiling beyond whic h the relative increase is not considered. That is, for example, if a relative increase of 10 dBA with a ceiling of 50 dBA is allowed and the existing level is 45 dBA, a leve l of 55 dBA would not be allowed. Similarly, if a floor of 40 dBA was established and the existing level is 25 dBA, 40 dBA rather than 35 dBA would be allowed. Fixed distance setbacks have also been discu ssed. Critics of this approach suggest that fixed setbacks do not ta ke into account the number or size of the turbines nor do they consider other potential so urces of noise within the project area. It is clear that like many other sources of noise, a uniform regulator approach for wind turbine noise has not been established either domestically or internationally. A draft report titled Environmental Noise and Health in the UK , published for comment in 2009 by the Health Protection Agency (HPA) on be half of an ad hoc expert group, provides insightful comments on the World Health Or ganization’s noise guidelines (WHO, 1999). The HPA draft report can be viewed at the following address: http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1246433634856 The HPA report states the following: It is important to bear in mind that the WHO guideline values, like other WHO guidelines, are offered to policymakers as a contribution to policy development. They are not intended as standards in a formal sense but as a possible basis for the deve lopment of standards. By way of overall summary, the 1998 NPL report noted [a British report titled Health-Based Noise Assessment Methods— A Review and Feasibility Study (Porter et al., 1998) as quoted in HPA 2009]: The WHO guidelines represent a consensus view of international expert opinion on the lowest noise levels below which the occurrence rates of particular effects can be assumed to be negligible. Exceedances of the WHO guideline values do not necessarily imply significant noise impact and indeed, it may be that significant impacts do not occur until much higher degrees of noise exposure are reached. The guidelines form a starting point for policy development. However, it will clearly be important to consider the costs and benefits of reducing noise levels and, as in other areas, this should inform the setting of objectives. (From: HPA, 2009, p. 77) The HPA report further states the following: Surveys have shown that about half of the UK population lives in areas where daytime sound levels exceed those recom mended in the WHO Community Noise Guidelines. About two-thirds of the popu lation live in areas where the night-time guidelines recommended by WHO are exceeded. (p. 81) That sleep can be affected by noise is common knowledge. Defining a dose-response curve that describes the relationship between exposure to noise and sleep disturbance has, however, proved surpri singly difficult. Laboratory studies and field studies have generated different results. In part this is due to habituation to noise which, in the field, is common in many people. (p. 82) Our examination of the evidence relating to the effects of environmental noise on health has demonstrated that this is a rap idly developing area. Any single report will, therefore, need to be revised within a few years. We conclude and recommend that anWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

4-15 independent expert committee to address these issues on a long-term basis be established. (p. 82)

The statements cited above from the HPA and WHO documents address general environmental noise concerns rather than concer ns focused solely on wind turbine noise.5-1 SECTION 5 

# Conclusions

Many countries have turned to wind energy as a key strategy to generate power in an environmentally clean manner. Wind energy enjo ys considerable public support, but it has its detractors, who have publicized their co ncerns that the sounds emitted from wind turbines cause adverse health consequences. The objective of the panel was to develop an au thoritative reference document for the use of legislators, regulators, and citizens simply wanting to make sense of the conflicting information about wind turbine sound. To this end, the panel undertook extensive review, analysis, and discussion of the peer-reviewed literature on wi nd turbine sound and possible health effects. The varied professional backgr ounds of panel members (audiology, acoustics, otolaryngology, occupational and environmenta l medicine, and public health) were highly advantageous in creating a diversity of info rmed perspectives. Participants were able to examine issues surrounding health effects and discuss plausible biol ogical effects with considerable combined expertise. Following review, analysis, and discussion, the panel reached agreement on three key points:

• There is nothing unique about the sounds and vibrations emitted by wind turbines.

• The body of accumulated knowledge about sound and health is substantial.

• The body of accumulated knowledge provid es no evidence that the audible or subaudible sounds emitted by wind turbin es have any direct adverse physiological effects. The panel appreciated the complexities involved in the varied human reactions to sound, particularly sounds that modula te in intensity or frequency. Most complaints about wind turbine sound relate to the aerodynamic soun d component (the swish sound) produced by the turbine blades. The sound levels are sim ilar to the ambient noise levels in urban environments. A small minority of those exposed report annoyance and stress associated with noise perception. This report summarizes a number of physic al and psychological variables that may influence adverse reactions. In particular, the panel considered “wind turbine syndrome” and vibroacoustic disease, which have been clai med as causes of adverse health effects. The evidence indicates that “wind turbine synd rome” is based on misinterpretation of physiologic data and that the features of th e so-called syndrome are merely a subset of annoyance reactions. The evidence for vibroa coustic disease (tissue inflammation and fibrosis associated with sound exposure) is ex tremely dubious at levels of sound associated with wind turbines. The panel also considered the quality of epidem iologic evidence required to prove harm. In epidemiology, initial case reports and uncontro lled observations of disease associationsWIND TURBINE SOUND AND HEALTH EFFECTS AN EXPERT PANEL REVIEW

5-2 need to be confirmed through controlled studie s with case-control or cohort methodology before they can be accepted as reflective of casual connections between wind turbine sound and health effects. In the area of wind turbin e health effects, no case-control or cohort studies have been conducted as of this date. Accordingly, allegations of adverse health effects from wind turbines are as yet unprov en. Panel members agree that the number and uncontrolled nature of existing case reports of ad verse health effects alleged to be associated with wind turbines are insufficient to advocate for funding further studies.

In conclusion:

1. Sound from wind turbines does not pose a risk of hearing loss or any other adverse health effect in humans.

2. Subaudible, low frequency sound and infrasou nd from wind turbines do not present a risk to human health.

3. Some people may be annoyed at the presence of sound from wind turbines. Annoyance is not a pathological entity.

4. A major cause of concern about wind turbine sound is its fluctuating nature. Some may find this sound annoying, a reaction that de pends primarily on personal characteristics as opposed to the intensity of the sound level.6-1 SECTION 6 

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# Additional References

Alberts, D. 2006. Primer for A ddressing Wind Turbine Noise. http://www.maine.gov/doc/mfs/windpow er/pubs/pdf/AddressingWindTurbine Noise.pdf

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Chatham-Kent Public Health Unit. 2008. The He alth Impact of Wind Turbines: a Review of the Current White, Grey and Published Literature 2008. http://www.windworks.org/LargeTurbines/Health%20and%20Wind%20by%20CK%20Health%20Unit.pdf

. Copes, R. and K. Rideout. Wind Turbines and Health: A Review of Evidence. Ontario Agency for Health Protection and Promotion 2009. http://www.oahpp.ca/Documents/Wind%20Turbines%20- %20Sept%2010%202009.pdf

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. Stelling, K. and D. Phyt. 2009. Summary of recent research on adverse health effects of wind turbines. http://windconcernsontario.files.wordpress.com/2009/08/adversehealth-effects-of-wind-turbines1.pdf

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6-9 Industrial Wind Action Grou p. 2009. Maine Osteopathic Association Resolution: Wind Energy and Public Health. http://www.windaction.org/documents/23515

. Kamperman, G. and R. James. 2008. Why noise criteria are necessary for proper siting of wind turbines. http://www.windturbinesyndrome.com/wpcontent/uploads/2008/11/kamperman-and-james-9-pp.pdf

. Kamperman, G., and R. James. 2008. The how to guide to siting wind turbines to prevent health risks from sound. http://www.savethebluffs.c a/archives/files/kampermanjames-8-26-08-report.pdf

. Klug, H. Noise from wind turbines—st andards and noise reduction procedures. http://www.sea-acustica.es/Sevilla02/envgen013.pdf

. Keith, S. E., D. S. Michaud, and S. H. P. Bly. 2008. A proposal for evaluating the potential health effects of wind turbine noise for projects under the Canadian Environmental Assessment Act. Journal of Low Frequency Noise, Vibration and Active Control, 27 (4):253-265. Ramakrishnan, R. 2007. Acoustic Consulting Repo rt Prepared for the Ontario Ministry of the Environment: Wind Turbine Facilities Noise Issues. Aiolos Engineering Corporation. https://ospace.scholarsportal.info /bitstream/1873/13073/1/283287.pdf

. Regan, B. and T.G. Casey. 2006. Wind Turbine Noise Primer , Canadian Acoustics Journal 34 (2). Rogers, A. and J. Manwell . Wright, S. 2002. Wind turbine acoustic noise. http://www.ceere.org/rerl/publications /whitepapers/Wind_Turbine_Acoustic_N oise_Rev2006.pdf / Soysai, H., and O. Soysai. Wind farm noise and regulations in the eastern United States. 2007. Proceedings of the Second Internatio nal Meeting on Wind Turbine Noise. Lyon, France: September 20-21, 2007. INCE/Europe. State of Rhode Island, Department of Environmental Management. 2009. Terrestrial Wind Turbine Siting Report

. http://www.dem.ri.gov/cleannrg/pdf/terrwind.pdf

. Ward, W.D, L.H. Royster, and J.D. Royster. 2003. Anatomy and Physiology of the Ear: Normal and Damaged Hearing. In The Noise Manual , Eds. Berger EH, Royster LH, Royster JD, Driscoll DP, Layne M. AIHA Press, Fairfax VA. Welgampola, M.S., S.M. Rosengren, G.M. Halmagyi, and J.G. Colebatch. 2003. Vestibular activation by bone conducted sound. Journal of Neurology, Neurosurgery and Psychiatry 74: 771-778.
Wilder, D.G., D.E. Wasserman, and J. Wasserm an. 2002. Occupational Vibration Exposure. In Physical and Biological Hazards of the Workplace , Ed. Wald PH, Stave GM. John Wiley and Sons, New York. World Health Organization (WHO). 2009. Nigh t Noise Guidelines for Europe. The World Health Organization, Geneva, Switzerland. http://www.euro.who.int/document/e92845.pdf

.

## A PPENDIX 

## A 

# Fundamentals of SoundA-1 APPENDIX A 

# Fundamentals of Sound

The following appendix provides additional background information on sound and how it is defined. One atmospheric pressure is given by 100,000 pa scals (Pa), where one pascal is one Newton per square meter (N/m 2 ), and a sound pressure of 94 dB re 20 μ Pa is given by 1 Pa (See later for decibels). The frequency of the fluctuations may be between 20 times a second (20 Hz), and up to 20,000 times a second (20,000 Hz) for the “audible” noise. Frequencies below 20 Hz are commonly called “infrasound,” although there is a very fuzzy boundary between infrasound and low frequency noise. Infrasound at high levels is audible. Low frequency noise might be from about 10 Hz to about 200 Hz. In addition to frequency, the quantitie s which define a sound wave include:

• Pressure, P

• Wavelength, λ

• Velocity, c = 340m/s approx, depending on temperature The velocity and wavelength are related by : velocity = wavelength x frequency, Relating frequency and wavelength by velocity gives
Freq Hz 16 31.5 63 125 250 500 1000 2000 4000 Wavelength

m 21 11 5.4 2.7 1.4 0.68 0.34 0.17 0.085

Low frequencies have long wavelengths. It is useful to develop an appreciation of frequencies and related wavelengths, since this helps an understanding of noise propagation and control. Sound pressure in a wave is force per unit of area of the wave and has units of N/m 2 , which is abbreviated to Pa. The sound pressure fluc tuates above and below atmospheric pressure by a very small amount. The sound power is a characteristic of the sour ce, and is its rate of production of energy, expressed in watts. The sound power is the fu ndamental property of the source, whilst the sound pressure at a measurement location depe nds on the transmission path from source to receiver. Most sound sources, including wind tu rbines, are specified in terms of their sound power. The sound power of a wind turbine is typically in the 100-105 dBA range, which is similar to that of a leaf blower. The sound power is used to predict propagation of the sound, where the source is assumed to be at the hub.APPENDIX A FUNDAMENTALS OF SOUND

A-2 

# Sound Levels

The decibel is the logarithm of the ratio betw een two values of a quantity such as power, pressure or intensity, with a multiplying cons tant to give convenient numerical factors. Logarithms are useful for compressing a wide ra nge of quantities into a smaller range. For example: log 10 10 = 1 log 10 100 = 2 log 10 1000 = 3 The ratio of 1000:10 is compressed into a ratio of 3:1. This approach is advantageous for handling soun d levels, where the ratio of the highest to the lowest sound which we are likely to encounter is as high as 1,000,000 to 1. A useful development, many years ago, was to take the ratios with respect to the quietest sound which we can hear. This is the threshold of hearing at 1,000 Hz, which is 20 microPascals ( μ Pa) (2x10 -5 Pa) of pressure for the average young he althy person. Sound powers in decibels are taken with respect to a reference level of 10 -12 watts.

When the word “level” is added to the word for a physical quantity, decibel levels are implied, denoted by L X , where X is the symbol for the quantity.

Pressure level 

### ⎥ ⎦ ⎤ ⎢ ⎣ ⎡

=

0 10 

### log 20 P P L p dB

where P is the measured pressure and P 0 is the reference pressure level of 2x10 -5 Pa A little calculation allows us to express the soun d pressure level at a distance from a source of known sound power level as Sound pressure level, L P = L w –20log[r] –11 dB

Where L p is the sound pressure level L w is the sound power level of the source r is the distance from the source This is the basic equation for spherical sound pr opagation. It is used in prediction of wind turbine sound but, in a real calculation, has ma ny additions to it, to take into account the atmospheric, ground and topographic conditio ns. However, as a simple calculation, the sound level at a distance of 500m from a source of sound power 100 dBA is 35 dBA. Equivalent level (Leq): This is a steady leve l over a period of time, which has the same energy as that of the fluctuating level actua lly occurring during that time. A-weighted equivalent level, designated LAeq, is used for many legislative purposes, including for assessment of wind turbine sound. Percentiles (LN)L These are a statistical measure of the fluctuations in overall noise level, that is, in the envelope of the noise, which is usually sampled a number of times per second, typically ten times. The most used percentiles are L90 and L10. The L90 is the level exceeded for 90 percent of the time and represents a low le vel in the noise. It is often used to assessAPPENDIX A FUNDAMENTALS OF SOUND

A-3 background noise. The L10 is the level exceeded for 10 percent of the time and is a measure of the higher levels in a noise. Modern co mputing sound level meters give a range of percentiles. Note that the percentile is a stat istical measure over a sp ecified time interval. 

# Frequency Analysis

This gives more detail of the frequency compon ents of a noise. Frequency analysis normally uses one of three approaches: octave band , one-third octave band or narrow band. Narrow band analysis is most useful for complex tonal noises. It could be used, for example, to determine a fan tone frequency, to find the frequencies of vibration transmission from machinery or to detect system resonances. A ll analyses require an averaging over time, so that the detail of fluctuations in the noise is normally lost.

Criteria for assessment of noise are based on dBA, octave bands, or 1/3-octave band measurements. These measures clearly give increasingly detailed information about the noise.

## A PPENDIX 

## B 

# The Human EarB-1 APPENDIX B 

# The Human Ear

Humans have ears with three general regions:

1. An outer ear, including an ear (auditory) canal

2. An air-containing middle ear that includes an eardrum and small bones called ossicles (three in mammals, one in other animals)

3. An inner ear that includes organs of hearing (in mammals, this is the organ of Corti in the cochlea) and balance (vestibular labyrinth) Airborne sound passes thorough the ear canal, making the eardrum and ossicles vibrate, and this vibration then sets the fluids of the cochlea into motion. Specialized “hair cells” convert this fluid movement into nerve impulses that travel to the br ain along the auditory nerve. The hair cells, nerve cells, and other cells in the cochlea can be damaged by excessive noise, trauma, toxins, ear diseases, and as part of the aging process. Damage to the cochlea causes “sensorineural hearing loss,” the most common type of hearing loss in the United States.

It is essential to understand the role of the middle ear, as well as the difference between air conduction and bone conduction. The middle ea r performs the essential task of converting airborne sound into inner ear fluid movement, a process known as impedance matching (air is a low-impedance medium, meaning that its mo lecules move easily in response to sound pressure, while water is a high-impedance me dium). Without impedance matching, over 99.9 percent of airborne sound energy is re flected away from the body. The middle ear enables animals living in air to hear very soft sounds that would otherwise be inaudible, but it is unnecessary for animals that live in wa ter, because sound traveling in water passes easily into the body (which is mostly water). Wh en a child has an ear infection, or an adult places earplugs in his ears, a “conductiv e hearing loss” dramatically reduces the transmission of airborne sound into the inner ear. People with conductive hearing loss can still hear sounds presented directly to the sk ull by “bone conduction.” This is how both humans and fishes hear underwater or when a vibrating tuning fork is applied to the head, but it requires much more acoustic energy than air conduction hearing.

## A PPENDIX 

## C 

# Measuring SoundC-1 APPENDIX C 

# Measuring Sound

A sound level meter is the standard way of measuring sound. Environmental sound is normally assessed by the A-weighting. Althou gh hand-held instruments appear to be easy to use, lack of understanding of their operation and limitations, and the meaning of the varied measurements which they can give , may result in misleading readings. The weighting network and electrical filters ar e an important part of the sound level meter, as they give an indication of the frequency components of the sound. The filters are as follows:

• A-weighting: on all meters

• C-weighting: on most meters

• Linear (Z-weighting): on many meters

• Octave filters: on some meters

• Third octave filters: on some meters

• Narrow band: on a few meters Sound level meter weighting networks are shown in Figure C-1. Originally, the A-weighting was intended for low levels of noise. C-weight ing was intended for higher levels of noise. The weighting networks were based on human hearing contours at low and high levels and it was hoped that their use would mimic the re sponse of the ear. This concept, which did not work out in practice, has now been abandoned and A- and C-weighting are used at all levels. Linear weighting is used to detect lo w frequencies. A specialist G-weighting is used for infrasound below 20 Hz. Figure C-1 shows that the A-weighting depresses the levels of the low frequencies, as the ear is less sensitive to these. There is general consensus that A-weighting is appropriate forestimation of the hazard of NIHL. With respect to other effects, such as annoyance, Aweighting is acceptable if there is largely middl e and high frequency noise present, but if the noise is unusually high at low frequencies, or contains prominent low frequency tones, the A-weighting may not give a valid measure. Compared with other noise sources, wind turbine spectra, as heard indoors at typical separation distances, have less low frequency content than most other sources (Pedersen, 2008).APPENDIX C MEASURING SOUND

C-2 FIGURE C-1 Weighting Networks

-80 -70 -60 -50 -40 -30 -20 -10

0 10

10 100 1000 10000 Frequency HzWeighting dB A C

## A PPENDIX 

## D 

# Propagation of SoundD-1 APPENDIX D 

# Propagation of Sound

The propagation of noise from wind turbines is determined by a number of factors, including:

• Geometrical spreading, given by K = 20log[r] –11 dB, at a distance r

• Molecular absorption. This is conversion of acoustic energy to heat and is frequency dependent

• Turbulent scattering from local variations in wind velocity and air temperature and is moderately frequency dependent

• Ground effects—reflection, topography and absorption are frequency dependent; their effects increasing as the frequency increases

• Near surface effects—temperature and wind gradients. The sound pressure at a point, distant from source, is given by

L P = L W - K—D - A A - A G (dB)

In which:

L P is the sound pressure at the receiving point

L W is the sound power of the turbine in decibels re 10 -12 watts K is the geometrical spreading term, which is inherent in all sources D is a directivity index, which take s non-uniform spreading into account

A A is an atmospheric absorption and other near surface effects term

A G is a ground absorption and other surface effects term Near surface meteorological effects are comple x, as wind and temperature gradients affect propagation through the air.

## A PPENDIX 

## E 

# Expert Panel MembersE-1 APPENDIX E 

# Expert Panel Members

Members of the expert panel are listed below. Biographies of each member are provided following the list. 

# Expert Panel Members

W. David Colby, M.D. Chatham-Kent Medical Officer of Health (Acting) Associate Professor, Schulich School of Me dicine & Dentistry, University of Western Ontario


### Robert Dobie, M.D.
Clinical Professor, Universi ty of Texas, San Antonio Clinical Professor, University of California, Davis



### Geoff Leventhall, Ph.D. Consultant in Noise Vibration and Acoustics, UK


### David M. Lipscomb, Ph.D. President, Correct Service, Inc.


### Robert J. McCunney, M.D. Research Scientist, Massachus etts Institute of Technology Department of Biological Engineering, Staff Physician, Massachusetts General Hosp ital Pulmonary Division; Harvard Medical School
Michael T. Seilo, Ph.D. Professor of Audiology, Western Washington University
Bo Søndergaard, M.Sc. (Physics) Senior Consultant, Danish Electr onics Light and Acoustics (DELTA)


# Technical Advisor

Mark Bastasch Acoustical Engineer, CH2M HILLAPPENDIX E EXPERT PANEL PARTICIPANTS

E-2 

# Panel Member Biographies

W. David Colby, M.D. W. David Colby M.Sc., M.D., FRCPC, is a fello w of the Royal College of Physicians and Surgeons of Canada in Medical Microbiology. Dr Colby is the Acting Medical Officer of Health in Chatham-Kent, Ontario an d Associate Professor of Medicine, Microbiology/Immunology and Physiology/Pharmacology at the Schulich School of Medicine and Dentistry at the University of We stern Ontario. He received his M.D. from the University of Toronto and completed his reside ncy at University Hospital, London, Ontario. While still a resident he was given a faculty appointment and later was appointed Chief of Microbiology and Consultant in Infectious Diseases at University Hospital. Dr Colby lectures extensively on antimicrobial chemot herapy, resistance and fungal infections in addition to a busy clinical prac tice in Travel Medicine and is a Coroner for the province of Ontario. He has received numerous awards for his teaching. Dr. Co lby has a number of articles in peer-reviewe d journals and is the author of the textbook Optimizing Antimicrobial Therapy: A Pharmacometric Approach. He is a Past President of the Canadian Association of Medical Microbiologists. On the basis of his ex pertise in Public Health, Dr Colby was asked by his municipality to assess the health im pacts of wind turbines. The report, titled The Health Impact of Wind Turbines: A Review of the Current White,Grey, and Published Literature is widely cited internationally.



### Robert Dobie, M.D. Robert Dobie, M.D., is clinical professor of otolaryngology at both the University of Texas Health Science Center at San Antonio and the Un iversity of California-Davis. He is also a partner in Dobie Associates, a consulting pr actice specializing in hearing and balance, hearing conservation, and ear disorders. The au thor of over 175 public ations, his research interests include age-related and noise-induced hearing loss, as well as tinnitus and other inner ear disorders. He is past president of the Association for Research in Otolaryngology, past chair of the Hearing and Equilibriu m Committee of the American Academy of Otolaryngology-Head and Neck Surgery, and ha s served on the boards and councils of many other professional organizat ions and scholarly journals.



### Geoff Leventhall, Ph.D. Geoff is a UK-based noise and vibration consultant who works internationally. His academic and professional qualifications incl ude Ph.D. in Acoustics, Fellow of the UK Institute of Physics, Honorary Fellow of the UK institute of Acoustics (of which he is a former President), Distinguished Internatio nal Member of the USA Institute of Noise Control Engineering, Member of th e Acoustical Society of America. He was formerly an academic, during which ti me he supervised 30 research students to completion of their doctoral studies in acou stics. Much of his academic and consultancy work has been on problems of infrasound and low frequency noise and control of low frequency noise by active attenuation

He has been a member of a number of Natio nal and International committees on noise and acoustics and was recently a member of two committees producing reports on effects of noise on health: the UK Health Protection Agency Committee on the Health Effects ofAPPENDIX E EXPERT PANEL PARTICIPANTS

E-3 Ultrasound and Infrasound and the UK Depart ment of Health Committee on the Effects of Environmental Noise on Health.


### David M. Lipscomb, Ph.D. Dr. David M. Lipscomb received a Ph. D. in Hearing Science from the University of Washington (Seattle) in 1966. Dr. Lipscomb taug ht at the University of Tennessee for more than two decades in the Department of Audiolo gy and Speech Pathology. While he was on the faculty, Dr. Lipscomb developed and di rected the department's Noise Research Laboratory. During his tenure at Tennessee and after he moved to the Pacific Northwest in 1988, Dr. Lipscomb has served as a consultant to many entities including communities, governmental agencies, industries, and legal organizations. Dr. Lipscomb has qualified in courts of law as an expert in Audiology since 1966. Currently, he investigates incidents to determine whet her an acoustical warning signal provided warning to individuals in harms way, and, if so, at how many seconds before an incident. With his background in clinical and research audiology, he undertakes the evaluation of hearing impairment claims for indust rial settings and product liability. Dr. Lipscomb was a bioacoustical consultant to the U. S. Environmental Protection Agency Office of Noise Abatement and Control (ONAC) at the time the agency was responding to Congressional mandates contained in the Noise Control Act of 1972. He was one of the original authors of the Criteria Document prod uced by ONAC, and he served as a reviewer for the ONAC document titled Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety . Dr. Lipscomb’s experience in writing and reviewing bioacoustical documentat ion has been particularly useful in his review of materials for AWEA regarding wind farm noise concerns.


### Robert J. McCunney, M.D. Robert J. McCunney, M.D., M.P.H., M.S., is board certified by the American Board of Preventive Medicine as a specialist in o ccupational and environmental medicine. Dr. McCunney is a staff physician at Massachuset ts General Hospital’s pulmonary division, where he evaluates and treats occupational and environmental illne sses, including lung disorders ranging from asbestosis to asthma to mold related health concerns, among others. He is also a clinical faculty member of Harv ard Medical School and a research scientist at the Massachusetts Institute of Technology Depart ment of Biological Engineering, where he participates in epidemiological research pe rtaining to occupational and environmental health hazards. Dr. McCunney received his B.S. in chemical en gineering from Drexel Un iversity, his M.S. in environmental health from the University of Minnesota, his M.D. from the Thomas Jefferson University Medical School and his M.P.H. from the Harvard School of Public Health. He completed training in internal medicine at Northwestern University Medical Center in Chicago. Dr. McCunney is past president of the American College of Occupational and Environmental Medicine (ACOEM) and an acco mplished author. He has edited numerous occupational and environmental medicine te xtbooks and over 80 published articles and book chapters. He is the Editor of all three editions of the text book, A Practical Approach to Occupational and Environmental Medicine , the most recent edition of which was published in 2003. Dr. McCunney received the Health Achievement Award from ACOEM in 2004.APPENDIX E EXPERT PANEL PARTICIPANTS

E-4 Dr. McCunney has extensive expe rience in evaluating the effects of noise on hearing via reviewing audiometric tests. He has written book chapters on the topic and regularly lectures at the Harvard School of Pu blic Health on "Noise and Health."
Michael T. Seilo, Ph.D. Dr. Michael T. Seilo received his Ph.D. in Aud iology from Ohio University in 1970. He is currently a professor of audiology in the Department of Communication Sciences and Disorders at Western Washington University in Bellingham, Washington where he served as department chair for a total of more than twen ty years. Dr. Seilo is clinically certified by the American Speech-Language-Hearing Asso ciation (ASHA) in both audiology and speech-language pathology and is a long-tim e member of ASHA, the American Academy of Audiology, and the Washington Speech and Hearing Association. For many years Dr. Seilo has taught courses in hearing conservation at both the graduate and undergraduate level. His special intere st areas include speec h perception and the impact of noise on human hearing sensitivity including tinnitus.

Dr. Seilo has consulted with industries on th e prevention of NIHL and he has collaborated with other professionals in the assessment of he aring-loss related claims pertaining to noise.


### Bo Søndergaard, M.Sc. (Physics) Bo Søndergaard has more than 20 years of experi ence in consultancy in environmental noise measurements, predictions and assessment. The last 15 years with an emphasis on wind turbine noise. Mr. Søndergaard is the conv enor of the MT11 work group under IEC TC88 working with revision of the measurement st andard for wind turbines IEC 61400-11. He has also worked as project manager for the follo wing research projects: Low Frequency Noise from Large Wind Turbines for the Danish Energy Authority, Noise and Energy optimization of Wind Farms, and Noise from Wind Turbines in Wake for Energinet.dk. 

# Technical Advisor Biography

Mark Bastasch Mr. Bastasch is a registered acoustical engi neer with CH2M HILL. Mr. Bastasch assisted AWEA and CanWEA in the establishment of the panel and provided technical assistance to the panel throughout the review process. Mr. Bastasch’s acoustical experience includes preliminary siting studies, regulatory development and assessments, ambient noise measurements, industrial measurements for model development and compliance purposes, mitigation analysis, and modeling of industrial and transportation noise. His wind turbine experience includes some of the first majo r wind developments in cluding the Stateline project, which when built in 2001 was the largest in the world. He also serves on the organizing committee of the biannual Internat ional Wind Turbine Noise Conference, first held in Berlin, Germany, in 2005.APPENDIX E EXPERT PANEL PARTICIPANTS

E-5 

# Acknowledgements

We acknowledge the following person for suggestions and comments on the manuscript. The final responsibility for the content remains with the authors.

Richard K. Jennings, M.D. —Psychiatrist, Retired