(This item appeared recently in AEI’s ongoing lay summaries of new research page)
The take-away from three new research papers appears to be that while significant proportions of the population – often around 25% – are affected by moderate wind farm noise, neither increasing wind farm noise nor even annoyance with noise lead inevitably to health effects. There is an entire separate body of research investigating various attitudinal aspects related to stress and health, which only muddy the waters as we try to interpret these direct studies on wind farm noise. Some studies indicate that attitudes toward a noise source can affect both annoyance and stress responses, and that a subjective sense of being threatened can likewise increase physiological responses to noise; however, once again, these correlations are far from universal, so they cannot be used to “explain away” either annoyance or health impacts that do take place, any more than annoyance can be used as a clear indication of eventual health effects.

There is far more gray than black and white in these reports. Still, they provide a concrete picture of annoyance and sleep deprivation increasing as turbine noise increases, along with a better sense of the proportion of affected neighbors who will experience these impacts at various distances and received sound levels. Clearly, 35-45dB is a range at which impacts on neighbors become far more widespread. The social question that will need to addressed is what proportion of nearby neighbors we will accept causing sleep deprivation or annoyance in: 10%? 20%? Where will we draw the line, beyond which we consider turbine placement too close? Read the lay summaries below the fold:

Minnesota Dept of Health
Minnesota Department of Health, Environmental Health Division. Public Health Impacts of Wind Turbines. May 2009. [DOWNLOAD REPORT HERE]

This state agency report provides a good overview of the current state of knowledge regarding wind farm noise propagation, with particular attention given to possible low frequency noise impacts. The report makes no dramatic recommendations, though the data presented suggests that audible and low-frequency noise could affect neighbors within a half mile to mile. Among the key pieces of information contained in this report, gleaned from previous research studies:

• A reminder that the 2007 report on wind farms and human health from the National Academies of Science concluded that “noise produced by wind farms is generally not a major concern beyond a half mile” (i.e., under a half mile can be problematic).
• Some individuals have extraordinary sensitivity to low frequency sound, up to 25dB more sensitive than presumed (average) thresholds at some frequencies
• Some people can dismiss and ignore repetitive but low intensity noise, while for others, the signal will grow and become more apparent and unpleasant over time. These reactions may have little relationship to will or intent, and more to do with previous exposure history and personality.
• The difference, in dB, between soft (acceptable) and loud (annoying) noise is much less at low frequencies, due to the our perceptual compression of the full audible range.
• Compiled data from two recent Swedish studies (summarized below) suggest that wind farm noise levels of over 40dB(A) lead to annoyance in about half the population, while slightly lower sound levels of 35-40dB(A) leads to annoyance in about a quarter of the population.
• A surprising study from New Zealand found that over half of household 2-2.5km AND 5-9.5km from wind farms could hear them at times (fewer in between heard them); these wind farms were in mountainous terrain, which likely explains the great distances at which they could be heard.
• Two charts from a 2006 report by the UK Department of Transport and Industry suggest that low frequency noise (LFN) from wind turbines can be well above audible levels, and above the UK’s night noise LFN criterion, at frequencies of 50-200Hz.

Summary of Three European Studies
Eja Pederson. Effects of wind turbine noise on humans. Third International Meeting on Wind Turbine Noise, Aalborg, Denmark, June 2009.

This review by one of the leading researchers of wind turbine noise, annoyance, and health, compiles data from three studies, two in Sweden and one in Holland. The results, while indicating clear thresholds for annoyance and sleep disruption at sound levels often experienced by wind farm neighbors, also illustrate the subtleties inherent in making generalizations based on ambiguous data. The author makes a key introductory point: that wind farms “often are placed in rural settings considered places with low exposure (to) environmental stressors….in such a setting, even when the levels are comparably low, (wind farm noise could) be perceived as a potential health risk.”

The heart of the studies shows a correlation between increasing noise levels and annoyance. This effect was clearly stronger in the two flat, rural areas, than in a study that took place in a more suburban, rolling landscape that had more other noises present. A dramatic increase in proportion of people annoyed by turbine noise took place when the noise was over 40dB(A); here, 25-45% reported annoyance in rural settings, and 10% in the suburban area. At 35-40dB, annoyance ranged from 16-20% in rural settings but was only 5% in suburban; at 30-35dB, annoyance hovered around 10% in rural areas.

(Note: some interpretations of this data set by industry analysts combine the rural and suburban results; since the suburban sample was larger, this lowers the annoyance averages.  If you are trying to understand impacts in a rural area, this is important to bear in mind.  Also, citing the overall average annoyance level in the entire study population of 1100-1800 people will create a misleadingly reassuring picture, since there are many more people living in more distant zones and exposed to very low sound levels; more interesting is to zero in on the sound levels where annoyance does tend to rise, and to work hard to remain below these levels.)

The studies showed no direct correlation between noise levels and health effects related to stress (including headaches, tiredness, tenseness, and irritability); this is not surprising, since at all noise levels, a majority of the population was not annoyed, so also not likely to be stressed. Among those experiencing annoyance, there was a correlation with stress effects, but it was far from universal (correlations generally in the 1.25 range).

Sleep disruption from any source was reported by 15-20% of rural respondents even at sound levels under 30db; some may interpret this as evidence of impact from wind turbines at very low sound levels, but it could as well be considered a baseline of sleep disturbance from non-wind farm causes. At sound levels of 30-40dB, 5-8% more rural residents reported sleep disruption, and as levels rose above 40dB, a total of 30-40% of rural residents reported being awakened. (Ed. note: the sleep disruption portion of the studies was not as consistent as other elements.  These number are limited to people reporting being woken at least once a month by noise.  There is a need for more specific studies of chronic sleep disturbance near wind turbines.)

More Insight into Noise Perception and Annoyance
Kerstin Persson Waye. Perception and environmental impact of wind turbine noise. Presentation at Internoise 2009.

This is another paper that re-analyzes results from the several previous studies, including the Swedish and Dutch ones cited above (Waye and Pederson were co-authors of one of these earlier studies), and adds several interesting and important points to the discussion.

First, she cites studies that suggest that the swishing nature of turbine noise is especially problematic, leading to a much higher correlation with annoyance than simple dB level measurements. Indeed, even at sound levels of only 35-40dB(A), when swishing was present, 45% of respondents reported being “rather” or “very” annoyed; over 20% were similarly annoyed at 30-35dB.

Waye delves too-briefly into studies addressing the connection between SEEING turbines and being annoyed by them. This is an especially difficult question, but she cites studies suggesting very high correlations between visibility and annoyance, much higher than the related correlation between visibility and audibility. This ties into other studies suggesting that those who don’t like seeing turbines, also don’t like hearing them; again, though, it’s important to remember that even these strong correlations are not universal, and many who experience noise issues are content to see turbines, if they are far enough away to not create audible disruptions to their recreational, work, and sleep life.

In parsing the data from the three studies also addressed by Pederson, above, Waye adds two key pieces of information: first, all these wind farms consist of relatively small turbines, by current standards: 500-800kW. Second, our consideration of annoyance thresholds at various dB levels is greatly enhanced by also including a graph showing that, in addition to those annoyed at each sound level, another 40-70% of the population could HEAR the turbines, but did not report annoyance. For example, at 30-35dB, over half of rural residents reported hearing the turbines, while only 8-12% were annoyed; at 35-40dB (within most global regulatory limits), 85% heard them, while just under 20% were annoyed; and at 40-45dB (within common US regulatory limits), 95% heard them, while 45% were annoyed.

Finally, Waye addresses a commonly reported finding: that annoyance levels are higher for wind turbines than for noise from less dynamic industrial sources, such as factories. She cites a study that shows that annoyance when indoors is pretty much the same, but that outdoors in rural settings, annoyance is significantly higher at sound levels above 35dB (annoyance at the one suburban wind farm was nearly identical to that from factory noise, again suggesting that expectations in rural setting plays a key role). Waye suggests that in rural settings, recreational and “restorative” aspects of outdoor experiences are impinged upon by wind farm noise. A final fascinating tidbit in her paper is that people who move from cities to the country are significantly more sensitive to noise than people who had always lived in the country; that is, those who actively chose to relocate to the country are more attached to the quiet nature of the landscape, while those who grew up there are more accepting of changes. (Ed. note: As with so many statistics in these studies, though, this should not be over-emphasized; surely many long-time locals also struggle with noise impacts. Indeed, the difference in sensitivity to noise, while an interesting finding, is just 15%)

Related recent posts on AEInews.org:

WHO Releases New Night Noise Guidelines (4odB outside)

Maine Medical Assoc Calls for State to Modify Permitting Process for Wind Farms

Noise Concerns Prompt Minnesota PUC Investigation of Setback Standards

Sleep Disturbance Expert Releases Report on Noise Effects Near Wind Farms

Also, you can see all posts related to Wind Turbines by clicking on the category link to the right.