Resource Documents: Noise (551 items)
Documents presented here are not the product of nor are they necessarily endorsed by National Wind Watch. These resource documents are provided to assist anyone wishing to research the issue of industrial wind power and the impacts of its development. The information should be evaluated by each reader to come to their own conclusions about the many areas of debate.
Author: Swinbanks, Malcolm; and Australia Senate Select Committee on Wind Turbines
Q1. You mention the NASA wind turbine research of the 1980s. Is that relevant to the type of wind turbines used today?
Research into very large (multi-megawatt) wind turbines began at NASA in 1975. Much of this work was undertaken by very competent aero-acousticians, drawing on experience gained in the context of propeller and jet-engine development, and which has successfully resulted in substantial improvements in aero-engine noise. They identified at an early stage why the existing “downwind rotor” turbines were so noisy, and in 1979 commenced theoretical and practical evaluation of the first very large “upwind-rotor” turbine, the 2.5 MW “MOD-2”. In this context, in 1981 they confirmed the predicted reduced noise characteristics, while also investigating the adverse power generation and noise effects associated with close spacings between wind-turbines. They subsequently identified additional circumstances under which the low-frequency and infrasound generation of such upwind-rotor turbines could be compromised, and performed important studies on the human perception of low-frequency noise and infrasound. The latter investigations initially concentrated on the noise characteristics of the earlier downwind-rotor turbines, but the underlying physics governing hearing perception relate also to the upwind-rotor configuration.
Over the intervening 25-35 years, the basic physics of aerodynamic noise generation has not changed, the adverse effects of unduly close-spaced wind-turbine interaction remain the same, and the characteristics of human hearing have not changed. These aspects all continue to have immediate relevance to modern wind-turbine installations, yet this research has often been dismissed as old-fashioned and irrelevant by the wind-development community.
Q2. How do wind turbines produce infrasound and is this hazardous to humans if they cannot hear it?
The infrasound is generated by the aerodynamic lift forces on the blades, which are necessary to provide the driving torque to rotate the blades and generate electrical power. Newton’s law requires that there are corresponding forces of reaction on the air passing over the blades. Although these forces may be comparatively “steady”, the constantly changing position of the blades means that the resultant force pattern acting on the surrounding air is also changing so that, inevitably, infrasound is generated. Additional factors, such as the difference between blades encountering slow moving air at the bottom of their cycle, and faster moving air higher up, causes further changes to the blade-lift and force pattern, which can result in higher intensity and more impulsive infrasound.
It has been considered that the levels of infrasound generated by wind turbines are too low to cause adverse health effects, but such opinions have often relied on a mistaken interpretation of the “threshold of hearing”. There have been numerous instances over the last 40 years where people have reported adverse effects at sound pressure levels which are too low for people to “hear” it, while recent research is starting to identify possible mechanisms by which this process may take place.
Q3. There seems to be a somewhat semantic argument regarding “sensitization” and “annoyance” related to wind turbine exposure. Can you explain what “sensitization” is?
This question is perhaps most easily answered from my own experience. From 1979 to 1981, I worked directly on the low-frequency noise and infrasound from a ground-based gas-turbine compressor installation in a rural area, which was causing complaints and sleep-disturbance for residents up to 1 mile away. When I initially started working at the site, I did not consider the noise to be excessive and in conditions of a brisk breeze it was barely perceptible even at 100 yards. After two years, however, I found that if I drove up to the site having just travelled on a noisy motorway,while still in the motor car with the engine running I could “sense” directly whenever the gas-turbines were operating. This was not an immediately audible effect, nor was it in any way associated with “annoyance”, but this “sensing” of whether or not the turbines were operating nevertheless prove to be unerringly accurate. This was a process of enhanced perception which had developed during my time spent on site, and which became increasingly apparent as time progressed.
Q4. You make comment regarding the inter-turbine spacing of wind farms and how this affects the noise produced. Could you explain this further?
When conducting ground-based noise testing of large fan-jet aero-engines, it is usual to suspend the engine on a gantry and mount an extremely large porous “golf-ball” enclosure over the inlet of the engine. Without this, the ingestion of turbulent airflow from ground-effect wind-shear can result in very substantially increased noise generation from the large ducted fan at the inlet of the engine. The porous “golf-ball” smoothes out this turbulence, to reproduce the much cleaner airflow characteristics similar to those encountered by an engine operating forward of the wing when the aircraft is in flight.
Without such measures, turbulent ingestion can unrealistically increase the measured noise levels of the aero-engine by as much as 15dB, which is completely unacceptable for precision noise research and certification.
Exactly the same situation now relates to the operation of wind-turbines. Closely spaced wind turbines result in the turbulent wake from an upstream turbine becoming incident on a wind turbine immediately downstream, and the resultant unsteady airflow over the blades of the latter causes increased fluctuating lift forces giving enhanced noise generation and a reduced blade life due to fatigue. As indicated above, the need to guard against such effects has been well-known to the aero-acoustics community for many years.
Q5. Would you care to elaborate on your comments concerning the change in human hearing threshold between noisy and quiet environments and explain how this effects people living in close proximity to wind turbines?
I first became aware of the effects of the variable hearing threshold when performing experiments in the active control of low frequency sound in the late 1970’s and early 1980’s. Such experiments involved generating low-frequency noise for extended periods of time, while frequently alternating between the unsilenced condition and then turning on the active silencing to yield significantly reduced noise levels. I found that there could be very different perception of the magnitude of the apparent change when going from long periods of the quiet condition (sensitive threshold of hearing) to the loud condition, compared to going from a protracted period of noisy exposure (raised threshold of hearing) to the quiet condition.
The hearing tests carried out by NASA in 1982 (referred to in my answer to Q1) confirm the relevance to wind-turbine noise. Tests of simulated wind-turbine impulsive low-frequency noise and infrasound under very quiet conditions showed perception could take place at a level significantly below the nominal threshold of hearing. Introducing an increased ambient background of 35dB required the simulated sound level to be increased by approximately 10dB in order for the sound to be perceived. With an ambient level of 45dB the level required for perception became even higher, being increased by a further 6dB.
Some acousticians have argued that since infrasound levels directly comparable to wind-turbine infrasound are not a problem in urban environments (55dBA), then they should not be a problem in rural environments (25dBA). This argument completely fails to take into account the very significant increase in hearing sensitivity in the rural environment. Perception and response in these two very different sound environments cannot be equated in this manner. An immediate consequence is that such levels can give rise to significantly greater sleep disturbance in the rural environment.
Q6. It appears that continued exposure to low-frequency noise and infrasound can result in progressively more acute physical sensitivity to the sensations. Could you elaborate on this for us?
I referred in my answer to Q3 to my own experience of increased perception and sensing ability, which for me appeared to have evolved entirely naturally. In a 2004 publication , Dr Leventhall stated “ If complainants spend a great deal of time listening to, and listening for, their particular noise, it is possible that they may develop enhanced susceptibility to this noise. Enhanced susceptibility is therefore a potential factor in long-term low frequency noise annoyance.” The only aspect of this statement with which I would disagree is that it places responsibility on the victim by implying that their own actions and behaviour have led to the enhanced susceptibility. But if the victim cannot escape the imposed disturbance, it is entirely likely that they will also be unable to escape the enhanced susceptibility.
I know sufferers from wind-turbine noise who report that the effects can be felt as pressure pulsations in the chest. One farmer has told me that he could even sense the wind-turbines while riding his tractor. So the overall nature of the sensations can amount to more than a simple impact on hearing.
A further comment is that I know of couples for whom the continuing stress of exposure to wind turbines has ultimately threatened the stability of their marriage. The long term consequences can result in more than just immediate stress-related health problems.
Q7. You comment on the differences between setback distances between Australia and the USA. Would you like to comment on what you consider to be the safe setback distances for wind turbines?
When I first became familiar with the problems of wind-turbines, it was immediately apparent that the setbacks such as 1000 feet and 1320 feet, which I encountered in the USA, were completely unacceptable. I then met people in the UK who were experiencing problems at 3000 feet, so I formed the opinion that a safe distance would be in the order of 5000-6000 feet. It should be noted that in the UK, the “ETSU” procedure is not to define a fixed setback distance, but rather to define permitted sound pressure levels and then to place the onus on the wind-developer to show that his proposed windfarm layout will not exceed these permitted levels. The overall assessment process takes substantial account of measured ambient sound pressure levels at various dwellings, coupled with anticipated projection of measured ground level wind speeds to the wind-turbine hub height, and estimation of the resultant wind-turbine noise generation under those ambient conditions.
Subsequently, however, my wife and I have experienced ( limited) sleep disturbance from the newly erected windfarm 3 miles to the south of us, under certain weather conditions. I have already described in my written testimony, the measurements that I had obtained at Ubly on the occasion that I became severely ill. At a later date, the Australian acoustician Les Huson sent me his infrasound measurements taken at the Macarthur windfarm, where residents were encountering severe adverse effects at a distance of 3 miles. I compared his infrasound signals to my Ubly measurements, and found them to be very similar indeed, so it came as no surprise that residents were reporting similar problems. It is quite apparent that for some windfarms, a distance even of 3 miles can be insufficient.
The problem is twofold. First, there is very little experience of the accurate prediction of the generation of infrasound and low frequency noise by windfarms, particularly if the wind-turbines are badly positioned with respect to each other. Secondly, the subsequent propagation of low frequency and infrasound is highly dependent on the geometry of the terrain, the temperature profile, and the wind-profile. These factors can be difficult to predict with a high level of confidence.
Thus, I regret that at this stage I cannot give a firmer recommendation as to appropriate setbacks, but to emphasize that as the size of windfarms is increased, so the need for greater setbacks becomes increasingly apparent.
Q8. There is a lot of controversy surrounding what is called the Nocebo Effect. Can you comment on whether or not you think that this could be an explanation for the adverse health effects reported by residents living in close proximity to wind farms?
My personal opinion is that attributing the problems suffered by people in close proximity to wind farms to the “Nocebo Effect” is simply a convenient “get-out”. There have been a sufficient number of examples where communities have welcomed the introduction of wind-turbines, only to discover the adverse effects after they commenced operation. Moreover, there are also common factors with respect to overall noise levels, or low-frequency noise levels and infrasound levels to indicate that such adverse effects are not of a completely random nature. In many circumstances they are only to be expected. Unfortunately, failure to acknowledge these problems, or attempts to dismiss them as “Nocebo Effects” can have the opposite effect, namely of strengthening opposition to wind farms. During the 1970’s and 1980’s, when I encountered noise problems of a similar nature, it was quite customary to acknowledge the problems and attempt to address them. Now the policy is often a complete refusal to acknowledge them.
Q9. What were your experiences when you investigated a wind farm in Ubly. How can you be sure the effects you experienced were due to the wind turbines and have you ever experienced this reaction again?
The sequence of events at Ubly started early in the evening, at a house located downwind of six turbines, with the nearest at 1500 feet. There was little or no wind at ground levels, but there was clearly wind at the height of the turbines which were running steadily but with little sound. Inside the house it was impossible to hear or feel anything. We set up instrumentation, and started taking 30-minute measurements which I then would analyse before undertaking the next recording using modified instrumentation parameters. I certainly did not consider that the measured infrasound levels were sufficient to be of significance. After 1 hour I began to feel lethargic with reduced concentration, after 3 hours I felt distinctly nauseous, but only after 3.5 hours did I start to attribute the problem to the wind turbines. After 5 hours I was extremely relieved to leave, only to find that my ability to drive was severely compromised, to an extent that I have never previously encountered.
The effects had started when I was working amongst the wind turbines, and finally abated 5 hours after I had left. Although I have encountered some adverse effects in the past from low frequency noise and infrasound, I have never before encountered anything of this severity.
On a few subsequent visits to this house under similar conditions I have again experienced the preliminary indications of this process, but I have always made a point of leaving promptly, before any effects have had time to build up.
Q10. A number of residents report sleep disturbance when turbines are operating. Do you think this could be due to the wind turbines and if so, are these effects serious?
The low-frequency levels and infrasound levels for some residents near to windfarms are such that it is only to be expected that they have experienced sleep disturbance. It is my understanding that protracted sleep disturbance can ultimately lead to more complex and serious medical effects. Dr Chris Hanning, a retired specialist from the sleep research laboratory in Leicester, England, whom I believe has given testimony to this Senate Hearing, has often commented on such medical effects.
Q11. Dr. Leventhall is somewhat critical of your work and conclusions. Can you give us your side of the story?
In written testimony prepared for the Kent Breeze 2011 hearings in Ontario, Canada, and in verbal testimony in 2013 in Alberta, Dr Leventhall has commented on my work. Several of his comments have resulted from his inaccurate recollection and description of my papers and presentations. But Dr Leventhall also stated that I had misunderstood 1982 NASA work on the perception of simulated low-frequency wind-turbine noise, arguing that it related only to old-fashioned downwind-rotor turbines. He had failed to appreciate that the relevant issue lies in the basic physics of the impulsive process. This physics applies not just to the impulsive low-frequency sound of the early wind-turbines, but also to the impulsive infrasound emissions from modern upwind-rotor turbines. Failure to quantify this correctly has led to many instances where modern-day acousticians have examined infrasonic wind-turbine power spectra from a superficial perspective and consequently have completely underestimated the likelihood of its perception.
In his 2013 testimony, Dr Leventhall stated of my work “he tends to overcomplicate things. He can’t do things in a sort of simple broad-brush clear way”. He also took me to task for having apparently failed to read properly the definitive 2004 paper of Moller and Pedersen  I had read and cited this paper in my very first wind-turbine submission in December 2009 – yet the specific issue which Dr Leventhall claimed that I “obviously did n’t read” is not mentioned in it. His comments related to my 2011 paper  in which I had started out by referring to an acknowledged problem for which no-one could offer any solution. I proposed a solution, and showed how it endorsed a commonly applied rule-of-thumb. My intention was to demonstrate that my investigations using rigorous methodology yielded a start point which could be confirmed, namely a result consistent with existing empirical evidence. I then developed this methodology further, drawing directly on Moller & Pedersen’s argument that at extremely low frequencies, it is the time history of the infrasonic waveform that is important. In this way, I could investigate methodically what consequences might follow-on from their statements.
It should be remarked that in the early 1970’s, it was extremely difficult to assimilate the vast amounts of data that often are associated with acoustic analysis. In those circumstances, there was often no alternative but to adopt a “broad-brush” approach. The advent of mini-computers and powerful digital analysis equipment later in that same decade transformed the nature of acoustics research and analysis, so that it was no longer necessary to rely on informed guesswork. This revolution became extremely important in such areas as the development of quiet aero-engines, or very quiet submarine design, together with efficient underwater sound detection.
I decided to apply similar methodology to the process of hearing perception, using no more than the established macro-level hearing characteristics which are well known to audiologists, but then examining what features emerge when one conducts dynamic simulation of these processes. Using this approach, I concluded that perception of infrasound may be possible to very much lower frequencies and sound pressure levels than has hitherto been considered to be the case. Moller & Pedersen’s paper states “Generally low-frequency and infrasonic sounds from everyday life are not pure tones alone, but rather combinations of different random noises and tonal components. It is however, impossible to make thresholds for all imaginable combinations of sounds that exist ….. “.
The unique and all-pervading noise characteristics of wind-turbines represents a situation where it is essential to make constructive inroads into this apparently “impossible” task. This necessarily requires a much more rigorous approach than simple “broad-brush” procedures.
Q12. What level of infrasound, low frequency noise would be safe in your view?
As a result of increasing familiarity with these problems, I have had to continually revise and lower my estimates of levels that would be considered to be safe or acceptable. I very recently met with a family who have been suffering for almost 6 years with the problem of sleep disturbance from an adjacent windfarm. Initially they could not sleep in their bedrooms. They converted the underground basement of their house into sleeping quarters, and found some immediate relief moving to this location. But then with the passage of time, they found that this was no longer satisfactory and they appeared to be becoming increasingly sensitive. So they constructed a dedicated sleeping chamber within the basement, with improved sound proofing which yielded measurably lower infrasound and low-frequency sound levels. Moving into this additional chamber was found to give further relief, but now in the longer term, even in this lower sound environment they are again finding their sleep patterns to be unsatisfactory. The noise characteristics of wind turbines are essentially unique, which results in them causing annoyance at much lower levels than more conventional noise sources (e.g. motor vehicles, railways and aircraft). For higher frequency audible components of the spectrum, external sound pressure levels of 35dBA would appear to be acceptable for the majority of people, but placing firm figures on safe levels of low-frequency noise and infrasound is still a difficult question given the potential for enhanced long-distance propagation under adverse weather conditions.
Q13. What research should be carried out as a priority to progress our understanding of this whole issue of adverse human effects from wind turbine emissions?
In the early 1980’s, NASA published a report containing a figure indicating that adverse effects had been reported in houses where the measured infrasound levels were significantly below the threshold of hearing. They commented that the effects might be due to subsequent induced vibration of the house structure by the pressure variations. At present, it is not known whether the effects are due to pure infrasound in the absence of any other sound components, or vibration induced by infrasound, or (according to my own analysis) by the interaction of low-level higher frequency noise causing the infrasound to become perceptible.
A first priority is to identify which of these mechanisms can successfully reproduce the symptoms in people who have already reported adverse effects from wind-turbines. Hearing processes and associated neurological response are extremely complex. It is well known that when people enter a well-designed anechoic chamber, which is intended to suppress all acoustic reflection and reproduce an entirely “dead” acoustic environment, they can often feel that they are being suffocated and suffering from lack of air. So even the complete absence of sound and reflections can result in strongly adverse physical reactions !;
It has even been considered that the adverse effects from wind-turbines might be induced by some electromagnetic influence. This would seem unlikely, however, because similar effects were reported back in the 1970’s from aero-engine test-beds, where there is no accompanying electromagnetic effect. Moreover, the long-distance effects appear to correlate with specific atmospheric sound propagation conditions, which would suggest that some aspect of sound generation is responsible.
Q14. What factors do you consider should be included in the development of appropriate setback distances for proposed windfarms?
I consider that it is important to obtain better assessment and prediction techniques for infrasound and low frequency noise from windfarms. Until comparatively recently, such measurements have only been made on a limited basis, and the incorrect use of long averaging times and third octave measurements has substantially compromised their usefulness. It is important to obtain consistent time-data records using instrumentation having appropriate characteristics for measurements at these frequencies. Deployment of low cost, very low frequency microbarometers, coupled with more conventional higher frequency microphones can be useful in providing a detailed overall perspective.
Setback distances are more appropriately defined according to likely expected noise levels, rather than being defined by single all-embracing distances which may not be relevant for extremely large windfarms.
There have been recent arguments  that dBA levels provide an adequate prediction of wind turbine low-frequency noise levels, resulting from a supposedly close correlation between dBA levels and low-frequency noise. This cannot be correct under all circumstances, because the effects of temperature gradient and wind-shear can significantly modify the propagation characteristics of low-frequency wind-turbine noise, whereas the frequency components which dominate dBA measurement are generally much less sensitive to these effects.
Q15. Do you consider we have enough information about the factors to be able to make assessments that ensure public safety?
There is still much to be learned about both the operating characteristics of large windfarms, and the detailed factors which can compromise health and well-being. I believe the most constructive improvement will come about when the already-known problems that residents can face are formally acknowledged. This would permit the adoption of mechanisms by which people who experience proven difficulties can receive reasonable compensation or redress, without having to undertake solitary and protracted legal action against heavyweight, subsidised organizations.
Q16. How do you propose that councils ensure they are able to assess the quality of information presented in windfarm consent applications?
This is a difficult question which I cannot answer fully. While there are many acousticians who appear to possess the necessary formal qualifications to address these issues, there can still be a considerable lack of real experience. Given that the deployment of wind-turbine technology continues to give rise to unsatisfactory installations, conventional qualifications alone do not yet guarantee a competent outcome. Pressure to conform to political or financial pressures relating to specific windfarm installations can also lead to compromise recommendations which may ultimately prove to be less than satisfactory.
Q17. You comment that low-frequency noise could cause a blockage in the helicotrema. If that is true, could this result in less of the low-frequency signal reaching the underside of the basilar membrane, thus it would not stimulate hearing so readily? However, could this cause an increase in pressure in the endolymph, which is connected to the utricle and saccule of the vestibular system? Could this pressure imbalance actually cause vestibular effects as the endolymph is connected to the utricle and saccule? Could this cause displacement of the otoliths and generate motion sickness and vertigo? Could you please comment on this?
This question Q17 suggests a credible overall explanation for the adverse effects. But the initial statement “less of the low-frequency signal reaching the underside of the basilar membrane, thus it would not stimulate hearing so readily” is incorrect. The purpose of the helicotrema is to provide pressure relief across the basilar membrane at very low frequencies. Natural background infrasound tends to rise in level as the frequency reduces, and it is important to prevent the basilar membrane from being unduly displaced by such natural pressure variations at these very low frequencies. Fluid motion through the open helicotrema ensures that the pressure tends to equalize on both sides of the membrane, thus minimizing displacement and reducing hearing sensitivity at such frequencies. But if the helicotrema is blocked, pressure balancing is prevented, and there is higher pressure on the upper side resulting in unwanted increased membrane excursions and resultant increased excitation of the cochlea hair cells. This in turn causes significantly increased sensitivity to very low-frequency sound (by as much as 20dB according to Dr Alec Salt.)
Q17 then considers whether such a one-sided pressure distribution can cause increased pressure within the endolymph – the separate central fluid which communicates with the utricle and saccule of the vestibular system. This quite possibly may be the case, so the same process which gives rise to increased hearing sensitivity may perhaps give rise to greater excitation of the otolith organs. If such enhanced excitation does indeed occur, it would then be expected to give rise to motion sickness and vertigo.
Q18. Is the sound pressure level important when considering biological effects of infrasound and low frequencies or could it be the frequency via acoustic resonance? Would this mean the level is less important?
I am not aware of any specific acoustic resonances within the conventional hearing organs which would account for extremely low frequency perception. At the higher frequencies, travelling waves along the basilar membrane “bunch together” at specific locations, giving a maximum resonant response to specific frequencies. Different locations along the basilar membrane are tuned to respond preferentially to different parts of the frequency range, with the highest frequencies concentrating at the input end of the cochlea (stapes) and the lowest frequencies concentrating towards the apex of the cochlea. At the very lowest frequencies, the entire basilar membrane tends to be excited.
The sensitivity of the vestibular organs which has been demonstrated by response to motion sickness testing does however show a broad bandwidth “resonant” type of behavior, with maximum response over the frequency range 0.07Hz to 0.7Hz. This corresponds to motions with period 1.4 seconds to 14 seconds. Over this frequency range, frequency can have as much or more importance in defining the response than the level. The fundamental blade rates of the largest, most modern wind-turbines do start to encroach on the upper end of this frequency range. It may be relevant that the adverse effects of wind-turbines appear to have become more apparent as the overall size has increased, and corresponding blade-rate frequencies have reduced. Until the precise mechanisms governing adverse health effects from wind turbines have been fully identified, such commentary is largely speculative, but may still represent relevant contributory information.
1. H.G. Leventhall. Low frequency noise and annoyance Noise & Health, Volume 6, 23 pp 59-72, 2004
2. H. Moller & C.S. Pedersen. Hearing at Low & Infrasonic Frequencies, Noise & Health, Volume 6, Issue 23, April-June 2004
3. M.A. Swinbanks. The Audibility of Low Frequency Wind Turbine Noise. Fourth International Meeting on Wind Turbine Noise Rome Italy 12-14 April 2011
4. R.G. Berger, P.Ashtiani, C.A. Ollson, M.W. Aslund, L.C. McCallum, H.G. Leventhall, L.D. Knopper. Health-based audible noise guidelines account for infrasound and low-frequency noise produced by wind turbines. Frontiers in Public Health, Volume 3, Article 31, February 2015
Additional Questions on Notice from Senator Anne Urquhart
AU1. What symptoms do you think are directly attributable to the operation of wind farms if there are any? What research are you basing this on?
For many years, it has been well-known and acknowledged that low-frequency noise can give rise to such symptoms as nausea, dizziness, headaches, feelings of pressure in the chest, while at nighttime it can give rise to very significant sleep disturbance. Over the years that I have worked with such noise, I have experienced several of these effects myself; these effects are not generally considered to represent an issue which is disputed in the acoustics community.
The transition between low-frequency noise and infrasound is often regarded as a “fuzzy boundary”, so it is not unreasonable to conclude that such effects would also be experienced in portions of the infrasound regime. This depends, however, on the existence of appropriate “perception”, so the thrust of my own research has been to investigate whether the present conventions for assessing infrasound perception are adequate. I have been able to show that these conventions are not adequate, and moreover that this is consistent with hitherto unexplained experimental reports in the peer-reviewed acoustics literature.
AU2. What proportion of the population do you think are susceptible to health impacts from wind farms if there are any? What factors do you think make people more susceptible than others? What research are you basing this on?
Based on the proportion of complaints arising from wind-farms, which are closely dependent on the setback distance, I would venture that around 5-10% of people in the immediate vicinity may suffer from direct physical effects. A much more common complaint is that of sleep disturbance, which over a long period of time can give rise to a very wide range of adverse physical effects.
One of the factors which is often not adequately taken into account is the fact that people cannot escape or gain relief from the exposure, nor can they be certain whether it will continue for hours or days at a time. This greatly enhances the psychological stress. Any noise which is purely transient, and is clearly going to come to an end ( for example the noise of a nearby combine harvester or large agricultural machine) is much more tolerable because it will only be of limited duration.
In a 2013 paper , Paul Schomer set out a convincing statistical argument indicating a strong correlation between people who suffer from motion sickness and those who experience adverse physical effects from wind turbines. But I have also been told of people who are not necessarily sensitive to motion, yet who have nevertheless experienced adverse effects from wind turbines.
AU3. How long do you think it takes from wind farm operations to manifest if there are any? What research are you basing this on?
I have read reports of people becoming adversely affected within 20 minutes in cases of nearby wind turbines. I know personally people who simply can no longer tolerate being in certain areas of their property and who react almost immediately, as a result of continuing exposure accumulated over several years. They do not “get used to it”. In my own case, I first experienced mild symptoms which I did not immediately recognize as due to wind turbines, after 1 hour. After 3 hours the symptoms were very clear and unpleasant, and after 5 hours I was only too glad to leave. I have based my conclusions on over 5 years of discussion and interaction with windfarm residents, both in the USA and the UK, together with my own direct experience.
AU4. What do you believe is an appropriate seback distance for wind farms? What research do you base this opinion on? In my answer to Q7 in the preceding set of questions, I remarked that with the passage of time and experience I have consistently revised and increased my assessment of an adequate setback distance. I believe the issue becomes increasingly important as the size of windfarms (ie number, land area, and individual size of turbines) is increased. I do not believe that sufficient consideration is being given to the cumulative effect of large numbers of turbines, or of the consequences of constructing multiple windfarms in close proximity.
AU5. You said in your testimony: “I believe that in a situation where people are reporting the effects that they observe while at the same time the operating characteristics of the wind farm are being monitored remotely, if you find that there is then a close correlation between those two situations, that does imply that there is a significant link and that people are reacting to real events.” Could you direct the committee to any peer-reviewed research published in an indexed medical journal that has found people’s perceived effects have been closely correlated to wind farm operating characteristics when they were operating within prescribed guidelines? If so, could you confirm what the statistical strength of this correlation was?
Unfortunately, I don’t think that there is to date any direct, peer-reviewed medical research which has addressed this specific issue. The recent work of Steven Cooper , an acoustician, represents probably the first quantitative study relating to this aspect. Such studies require close cooperation between the community and the windfarm operator.
In oral questions from the committee, I was asked (the equivalent of) whether I considered a success rate of 1/3rd in this particular context represented an adequate measure of statistical confidence. If one tosses a coin many times, one would expect to guess correctly “heads or tails” on average 50% of the time. In that particular context, a success rate of only 1/3rd would be a poor result, implying a problem with either the coin or the process. But suppose you have one person placed in an enclosed, windowless sound-proof room, who over an extended time interval tosses a coin many times at completely random well-separated instants, and allows it to land each time on the floor. Another person outside the room is asked to press a button whenever he thinks the coin has just landed. Under such circumstances, a success rate of 1/3rd would be a result indicating that some form of perception is likely to be taking place.
5. Schomer P, Edreich J, Boyle J, Pamidighantam P (2013). A proposed theory to explain some adverse physiological effects of the infrasonic emissions at some wind farm sites. 5th International Conference on Wind Turbine Noise 28-30, August 2013
Public Hearing, 23 June 2015
Parliament House, Canberra, ACT
Author: Castelo Branco, Nuno; Alves-Pereira, Mariana; et al.
In November 2006, 4 Industrial Wind Turbines (IWT) were installed in the vicinity of a residential dwelling in Portugal. In March 2007, this team was contacted by the family requesting assistance in dealing with their Infrasound & Low Frequency Noise (ILFN) problem that they claimed was being generated by the IWT. The family began legal proceedings for the removal of the IWT, and in September 2007, this team’s first report was presented at the 2nd International Meeting on Wind Turbine Noise. In June 2010, a follow-up report of this case was presented at the 14th International Meeting on Low Frequency Noise and Vibration and its Control, wherein ILFN-induced pathology was confirmed through histology in this family’s thoroughbred horses. The goal of this report is to provide second follow-up to this case, five years later.
Nuno A. A. Castelo Branco, M.D., Senior Surgical Pathologist
Mariana Alves-Pereira, Ph.D., Biomedical Engineer, Lusófona University
Augusto Martinho Pimenta, M.D., Senior Neurologist, Julio de Matos Hospital
José Reis Ferreira, M.D., Senior Pneumologist, Clínica Doentes Pulmonares
Presented at EuroNoise 2015, 31 May–3 June, Maastricht, The Netherlands
Author: Castelo Branco, Nuno; Alves-Pereira, Mariana; et al.
Segments of the general population who complain about infrasound & low frequency noise (ILFN) in their homes or in their workplaces continue to increase. These individuals often complain about similar sets of concurrent symptoms, and frequently attribute their ailments directly to ILFN exposure. Oftentimes, however, routine clinical evaluations of these individuals reveal no apparent dysfunction, and patients with persistent complaints are subsequently referred to psychology or psychiatry health professionals. The goal herein is to present an objective clinical protocol that scientifically evaluates these complaints, leading to the elimination of malingerers, and to the proper medical assistance of those developing ILFN-induced lesions.
Nuno A. A. Castelo Branco, M.D., Senior Surgical Pathologist
Mariana Alves-Pereira, Ph.D., Biomedical Engineer, Lusófona University
Augusto Martinho Pimenta, M.D., Senior Neurologist, Julio de Matos Hospital
José Reis Ferreira, M.D., Senior Pneumologist, Clínica Doentes Pulmonares
Presented at EuroNoise 2015, 31 May–3 June, Maastricht, The Netherlands
Author: Huson, Les
Microbarometers have been used to quantify the infrasonic emissions (0.05Hz to 20Hz) from five wind farms in Victoria, Australia. The wind farms measured include; Macarthur wind farm (140 turbines type Vestas V112 3MW); Cape Bridgewater (29 turbines type MM82 2MW); Leonards Hill (2 turbines type MM82 2MW); Mount Mercer (64 turbines type MM92 2MW), and; Waubra (128 turbines 3 types of Acciona Windpower 2MW).
Upwind indoor measurements at the Macarthur wind farm during an unplanned shutdown from full power and subsequent startup to 30% load has shown that stationary turbines subject to high winds emit infrasound pressure below 8 Hz at levels similar to the infrasound emissions at blade pass frequencies and harmonics.
The stationary V112 turbine infrasound emissions are caused primarily by blade and tower resonances excited by the wind. It is apparent from the mismatch of resonances and blade pass frequency components that Vestas have carefully designed this unit to minimise fatigue of the wind turbine.
Short range (up to 2km) measurements from the Leonards Hill wind farm have shown the determination of attenuation rate with distance to be problematic due to interference between the two turbines. A model to explain the unexpected attenuation results at Leonards Hill has demonstrated that the commonly observed amplitude modulation of blade pass tones is the result of changing phase between turbine rotor speed and changes in wind speed.
Long range measurements from two different wind farms over a distance of 80km have shown that infrasound below 6Hz has a propagation loss approximating 3dB per doubling of distance.
Les Huson, L Huson & Associates, Woodend, Victoria, Australia
6th International Conference on Wind Turbine Noise, Glasgow, 20-23 April 2015