Claims of adverse health effects of the low frequency or infrasound vibrations caused by wind power stations are not supported by the newest, most long-ranging findings on the subject.
A long-term government-commissioned study conducted by the Technical Research Centre of Finland (VTT) and others found that waves of infrasound cause no measurable changes in human physiology, and could not be detected by the human ear in rigorous testing.
Project leader Panu Maijala from VTT said that the wind power industry can now breathe a sigh of relief, after years of unsubstantiated public sentiment criticising wind turbine construction.
The chair of the managerial research team, Vesa Pekkola from the Ministry of Social Affairs and Health, predicted the results of the study will be significant in assuaging public misgivings.
"We were quick to make sure that the research must be utterly airtight in terms of scientific reliability," Pekkola said.
Maijala also emphasised the high quality of the research, which he said was conducted by "the best researchers in the country".
The VTT study used long-term measurements, listening tests and questionnaires to investigate the properties of infrasound — a sound vibration whose frequency is below the range of human hearing.
Measurements showed that the infrasound levels in rural areas with wind power parks were about the same as levels in a regular urban environment.
Maijala did say he was surprised to see occasional spikes in the volume of the frequency, going up to 102 decibels.
The main frequencies of the infrasound were between 0.1 and 1.0 hertz (Hz), which is well below the hearing range of the human ear (16-20 Hz). The lower the frequency, the louder the sound must be for it to be audible.
Maijala said he considers it theoretically possible that some individuals might be able to hear the loudest infrasounds caused by the wind turbines. He emphasised that no changes in physiology were discovered in the VTT study.
In the study, people who claimed their symptoms were caused by infrasound were not found to be able to hear the low frequencies any better than people who did not claim it as a cause. Their autonomous nervous systems were not found to be any more activated by the waves than those of asymptomatic test subjects.
The research took note of prior international studies on infrasound and health, but new long-term measurements were also taken at two wind power parks. Both the Kurikka wind farm and the Kopsa area in Raahe contain 17 wind turbines.
Researchers took measurements both indoors and outside, inside the wind power plant and beyond it, for 308 days.
"Usually measurements take a day or two to produce. The data we collected is rare, because we were able to measure the frequencies in people's homes for an extended period," Maijala said.
Maijala pointed out that the study was conducted on apartments and houses whose residents had moved away due to perceived wind-power related health symptoms. Maijala said he spent several days in another house near the Kopsa wind farm.
"The countryside is so quiet you can hear your own thoughts, but still the frequency didn't affect my sleep at all. Granted, I was there only a short while."
The study points out that for some sufferers, symptoms may be brought on by the so-called nocebo effect, where strong belief in negative effects can bring some of them about. People may also assign blame for their real, underlying ailments to the wind turbines in error or bad faith.
The unusually broad study was conducted by VTT, the University of Helsinki, the Finnish Institute of Occupational Health and the Finnish Institute for Health and Welfare (THL).
Pekkola said that no national or international criteria for the evaluation of infrasound effects existed prior to the study, published in late 2019. Concrete results have been in high demand around the globe.
"There have been a lot of people claiming that infrasound is a health risk. Now we have the evidence with which to approach those claims," Pekkola said.
As a world first, the study is piquing interest internationally, too.
"Similar research is underway in Germany and Australia, but their results aren't in yet," said Maijala. "I await them eagerly. I believe this study of ours will become a major reference point."