As renewable energy began to take off around the turn of the millennium, a New England pediatrician hypothesized that certain adverse health conditions could be attributed to the acoustic effects of nearby wind turbines. She interviewed a handful of select individuals, drew conclusions, invented the term “Wind Turbine Syndrome,” and wrote a book about it. While her research was not peer reviewed nor was it accepted for publication in any reputable scientific journal, the phrase caught on, and, to this day, I continue to see anti-wind signs near cornfields in our community. Although the physician in question didn’t conduct a thorough scientific study, her book inspired actual researchers to take a look at the acoustics of wind turbines and their potential impact on human physiology. Let’s see what science has to say about it.
Background
Acoustic levels are measured in decibels (dB), a logarithmic scale that indicates the intensity (loudness) of a sound. Since the human ear doesn’t have a flat frequency response, scientists developed a normalized unit, the A-weighted decibel (dBA), which takes into account both the sound intensity and the ear’s response to it. In general, for frequencies (pitches) at the lower and higher ends of the human hearing range, dBA levels will be lower than dB levels; for midrange frequencies, dB and dBA are nearly the same. The Occupational Safety and Health Administration (OSHA) measured various sounds and normalized them to a dBA scale.
To develop better models of wind farm noise, researchers measured sound intensity levels at various points (the black dots in the following image) near a 5 MW turbine. We can see from the figure that the sound levels within a few hundred meters of the turbine are 40 to 50 dB—similar to those in urban locales; beyond that, it’s little more than a whisper. This is one reason for setback regulations, which vary by region.
The Science of Sound and Its Impact on Humans
In 2009, the American and Canadian Wind Energy Associations (AWEA and CanWEA) assembled an international panel of experts in the fields of acoustics and physiology—all with established research records—and published the report Wind Turbine Sound and Health Effects: An Expert Panel Review. The study concluded that wind turbines produce infrasound (frequencies below the 20 Hz human hearing threshold) and low-frequency sounds, but found that there is no known “receptor” mechanism by which these sounds affect human physiology. Given the significant amount of research on the physiological effects of sounds, it’s unlikely that such a mechanism exists.
The researchers did acknowledge that a small number of people found the turbines’ faint and somewhat irregular “wooshing” sound to be slightly annoying and a potential source of stress. They concluded that the so-called “wind turbine syndrome” is most likely related to annoyance levels and not to a physiological condition. According to the report, “The evidence for vibroacoustic disease (tissue inflammation and fibrosis associated with sound exposure) is extremely dubious at levels of sound associated with wind turbines.”
In fairness, I should point out that the aforementioned study was sponsored by two agencies that advocate on behalf of wind power, so it’s reasonable to at least question the results. The researchers have no affiliation with those entities, are well-established experts in their respective fields, and their report cites more than 100 scientific studies, many of which were published in reputable, peer-reviewed journals.
Acoustics, a peer-reviewed open-access journal with no affiliation to the wind industry, recently published a special issue on wind turbine noise. Researchers noted the wealth of existing knowledge about the emission, propagation, testing and control of wind turbine noise, but agreed that research in these areas should continue. The report suggested developing better computer models of wind farm noise, in order to stay current with turbine technology and to address varying wind farm topologies, meteorological conditions and the interaction of multiple turbines on a farm. These models could lead to better setback distance calculations based on multiple variables. It also determined that, at worst, wind turbine noise may be annoying to some individuals, but causes no adverse physiological effects in humans. They did suggest the need for additional research on the impact that the noise might have on wildlife.
Who Finds the Sound Annoying?
A study conducted in Australia found a relationship between a person’s predisposition toward wind power and the likelihood of their noticing adverse symptoms and attributing them to nearby wind farms. The researchers noted that most, but not all, of the individuals who complained about wind farm noise were those opposed to wind power—possibly for political reasons. Likewise, those who considered the technology entirely benign tended to have pro-wind political tendencies. (Note that these are the opinions of average citizens, not scientists conducting research. While scientists have their biases too, those are generally exposed and filtered out by the peer-review process.) Another study attributed many of the reported symptoms to the “nocebo effect,” a sort of self-fulfilling prophecy in which the expected symptoms become noticeable regardless of actual stimuli.
The Bottom Line
As you can see, there is no empirical data linking wind turbine noise to any physiological health problems in humans. It’s possible that annoyance, which may be due to real or imaginary conditions, could lead to a certain amount of psychological distress in some individuals, but the evidence supporting that hypothesis is questionable at best.
In an era where some people claim that wind turbines cause cancer (they don’t) but that coal is clean (it isn’t), it’s important for citizens to understand the difference between science and “gut feelings.” Only one is based on physical evidence and is subjected to rigorous evaluation; the other is whatever someone wants it to be. Everyone wants a sustainable future; engineers use science to make it happen.