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MeCDC home > Wind Turbines Neuro-Acoustical Issues

Wind Turbines Neuro-Acoustical Issues

Dora Anne Mills, MD, MPH Maine CDC/DHHS
June, 2009

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1.  What protections are in Maine law regarding excessive noise and vibrations? 

Maine DEP has rules that apply to all developments in unorganized areas of the state and in all municipalities without a more restrictive noise ordinance.  The rules recognize in its text that excessive noise can degrade health and welfare of nearby neighbors, and they provide limits based on the type of development in the area surrounding the noise.  For instance, they limit noise levels for routine operation of a proposed development: to 75 dBA at any time; to 60 dBA during the daytime and 50 dBA during the nighttime for non-commercial and non-industrial areas; and to 55 dBA daytime and 45 dBA nighttime for areas in which ambient sounds are 45 dBA or less daytime or 35 dBA or less nighttime. 

Maine DEP also has retained the services of a noise expert to review noise study submissions as part of wind turbine applications and compliance evaluations. 

DEP’s ambient, post development monitoring at the Mars Hill wind farm shows dBA levels higher than 45, sometimes exceeding 60 when there are windy conditions both at ground level and at turbine height.  This presents an example of how ambient noise from wind at these locations (which is why turbines are placed there) is in excess of the optimal nighttime 45 dBA.  The DEP rules and compliance monitoring provide for distinguishing between the ambient contribution to noise and that from turbines at wind farms.

In summary:  Maine law appears to essentially place a 45 dBA noise limit on most wind turbine projects in Maine.  A 5 dBA variance to limits may be granted upon specific findings that concern pre-development existing ambient noises that are in excess of a particular standard.  For compliance with the rule, noise levels are measured at the boundary of the property owned by the proposed developer. 

Sources: 

2.  What do different noise levels compare to? 

40 dBA is comparable to a quiet room.  55 dBA is comparable to a household room or office in which there is normal background vibration and sounds such as is commonly found from household appliances.


Canadian Centre for Occupational Health and Safety
(see www.ccohs.ca/oshanswers/phys_agents/noise_basic.html ).

 

3.  What kinds of noises are expected from wind turbines? 

According to several resources, new wind turbines are relatively quiet, and meet federal and international standards and regulations for noise, including Maine’s regulations. 
According to the US Department of Energy, a modern wind farm at a distance of 750 – 1,000’ is no louder than a kitchen refrigerator or a moderately quiet room. 

However, there are people who live about these distances from wind turbines who disagree with this federal agency statement.  It appears from the research that distance from the wind turbine, height of the wind turbine relative to the surrounding topography, the quality of the sound (repetitive low frequency sound), wind conditions, and wind direction all affect how the wind turbine noise affects people.  Research done on wind turbines, airport and other sources of noise indicates that annoyance levels are difficult to assess.  However, taking in account the above factors as well as careful measurements need to be considered when siting wind turbines near residential properties. 

Sources: 

4.  Are there health effects to the levels of sound heard by wind turbines?

According to a 2003 Swedish EPA review of noise and wind turbines: 
“Interference with communication and noise-induced hearing loss is not an issue when studying effects of noise from wind turbines as the exposure levels are too low.”

In my review I found no evidence in peer-reviewed medical and public health literature of adverse health effects from the kinds of noise and vibrations heard by wind turbines other than occasional reports of annoyances, and these are mitigated or disappear with proper placement of the turbines from nearby residences.  Most studies showing some health effects of noise have been done using thresholds of 70 dBA or higher outdoors, much higher than what is seen in wind turbines. 

Sleep disturbance is another commonly raised concern, and the WHO guidelines for community noise recommend that nighttime outdoor noise levels in residential areas not exceed 45 dBA, which is consistent with Maine law.

Sources:

5.  What about low frequency noises (LFN)?

Some have pointed to LFN emitted from wind turbines as a possible source of adverse health effects.  The reasons LFN are focused on include: LFN encounter less absorption as they  travel through air than higher frequency sound, so they persist for a longer distance; the amount of sound transmitted from the outside to the inside of a building is higher with LFN; and some models for assessing impact of noise do not adequately include LFN. 

Low frequency and infrasound (lower than what is perceptible) vibrations are very common in our background, and known to be emitted from many household appliances and vehicles as well as in neighborhoods near airports and trains.  Exposure to very intense LFN can be annoying and may adversely affect overall health, though these levels appear to be more intense than what is measured from modern wind turbines. 

The DEP noise regulations are based on the “A” frequency range of noise, which measures the higher frequency end of the noise spectrum, and is denoted with the term dbA.  Because the dbA measurement deemphasizes noises from the lower end of the frequency spectrum (or “C” weighted noise, dbC), Maine DEP has been evaluating noise models and predicted noise levels from proposed wind power facilities using a handicapping system that requires an applicant to prove that dbA noise levels will be at such a level at property boundaries that they are effectively controlling for low frequency noises in the dbC range.  The Land Use Regulation Commission has required monitoring for dbC noise at one of its recently permitted wind turbine facilities in order to evaluate dbC noise levels at property boundaries.

One recent study commonly cited by proponents of the belief of the physiological impacts of LFN is:  “Tuning and sensitivity of the human vestibular system to low-frequency vibration”, Todd, et al.  Neuroscience Letters, 2008, which can be found at:  http://www.ncbi.nlm.nih.gov/pubmed/18706484. This study indicates that the human vestibular system is sensitive, which means it shows a physiological response, to low-frequency and infrasound vibrations of -70 dB, indicating that human seismic receptor sensitivity of the vestibular system may possibly be on par with the frog ear.  However, sensitivity, i.e. showing a physiological response, does not mean there are adverse effects. 

Summary: 
Reviews found in peer reviewed journals of the possible health effects of low frequency noise have not found evidence of significant health effects (several references are listed below).

Sources: 

“Infrasound from wind turbines is below the audible threshold and of no consequence. Low frequency noise is normally not a problem, except under conditions of unusually turbulent in flow air.  The problem noise from wind turbines is the fluctuating swish. This may be mistakenly referred to as infrasound by those with a limited knowledge of acoustics, but it is entirely in the normal audio range and is typically 500Hz to 1000Hz. It is difficult to have a useful discourse with objectors whilst they continue to use acoustical terms incorrectly. This is unfortunate, as there are wind turbine installations which may have noise problems. It is the swish noise on which attention should be focused, in order to reduce it and to obtain a proper estimate of its effects. It will then be the responsibility of legislators to fi x the criterion levels, However, although the needs of sensitive persons may influence decisions, limits are not normally set to satisfy the most sensitive.”

6.  What are the health benefits to wind turbines? 

  • There are tremendous potential health benefits to wind turbines, including reductions in deaths, disability, and disease due to asthma, other lung diseases, heart disease, and cancer.  Maine has among the highest rates in the country of asthma and cancer. 
  • Wind turbines mean less dependency on foreign oil and coal that contribute to global warming and pollution (coal produces carbon dioxide, acid rain, smog, particulate pollution, carbon monoxide, and mercury), which in turn contribute to the diseases above. 
  • According to the Maine DEP, if Maine generated 5% of its electricity from wind power, there would be significant pollution cuts: 
    • 464,520 tons per year of CO2
    • 252 tons per year of SO2
    • 147 tons per year of NOx

7.What about a moratorium on wind turbine projects?

  • I do not find evidence to support a moratorium on wind turbine projects at this time.  The articles cited by those who are in favor of a moratorium are either from non-peer reviewed journals (though some are labeled as “peer reviewed”) or are misinterpreted analyses from peer reviewed journals. 
  • If there is any evidence for a moratorium, it is most likely on further use of fossil fuels, given their known and common effects on the health of our population. 

Basic Wind Turbine Noise-Related Resources:

  • US Dept of Energy’s New England Wind Power Website on Wind Turbine Sound – this has a good summary and links to references
  • Massachusetts DEP Regulations
    “A source of sound will be considered to be violating the Department's noise regulation (310 CMR 7.10) if the source: Increases the broadband sound level by more than 10 dB(A) above ambient, or Produces a "pure tone" condition - when any octave band center frequency sound pressure level exceeds the two adjacent center frequency sound pressure levels by 3 decibels or more. These criteria are measured both at the property line and at the nearest inhabited residence. Ambient is defined as the background A-weighted sound level that is exceeded 90% of the time measured during equipment operating hours. The ambient may also be established by other means with the consent of the Department.”
  • Ongoing Research is being done by the US Dept of Energy Wind Turbine Aeroacoustic Research:
    “Turbine noise can be caused by rotor speed, blade shape, tower shadow, and other factors. The program is sponsoring both wind tunnel and field tests to develop a noise prediction code that turbine manufacturers can use to ensure that new rotor designs and full systems aren't too noisy. This is especially true for high-growth U.S. markets for small wind turbines that will demand quieter rotors, especially when turbines are sited in residential neighborhoods. Small turbines operate at high rotational speeds and tend to spin even if they are furled (pointed out of the wind).
  • Background Information on Noise: