Meight infrasound from wind turbines actually sick, as some sources claim? A specialist colloquium recently held in online format by the Federal Institute for Geosciences and Natural Resources (BGR) dealt with this question, among other things.
Infrasound is sound waves with a frequency below 16 Hertz. Although we humans cannot hear these signals, we can feel them as vibrations at high sound pressure levels. Household appliances, vehicles and airplanes, among others, emit infrasound. However, physical impairments have only been seriously discussed since wind turbines have been installed on a larger scale. Critics of wind power in particular have been claiming for years that people who live near wind farms should fear damage to their health due to the infrasound generated by wind turbines.
In general, the following applies to sound: the lower the frequency, the higher the sound pressure level must be for us to notice it. The hearing threshold at a frequency of 800 Hertz is 0 decibels, at 50 Hertz it is 40 decibels. At 4 hertz, in the infrasound range, the perception threshold is more than 100 decibels.
Higher infrasound dose in breaststroke
Acoustics expert Swen Müller from NTi Audio, who worked for years in the acoustics laboratory of the Brazilian National Institute of Meteorology, has long been concerned with the question of whether infrasound can have a negative impact on human organs. At the research meeting, he dealt, among other things, with a study from 2020. At the time, the cardiologist Christian-Friedrich Vahl from Mainz Medicum had presented data that were supposed to show that heart muscle cells that were exposed to infrasound increased their ability to contract by up to 18 percent was reduced. Müller noted that in the breaststroke, due to hydrostatic pressure, a single thoracic push produces a higher infrasound dose than that detected in Vahl’s experiment. He also suspected that Vahl’s experiment had effects that were not due to the infrasound, since the container in which the samples were kept did not appear to be completely airtight.
Influence on the vestibular system?
Müller also addressed the frequently asked question of whether infrasound from wind turbines might affect the vestibular system in the inner ear, which is responsible for the sense of balance, and thereby cause symptoms such as nausea and dizziness. By analyzing the measurement data from the Federal Institute for Geosciences and Natural Resources at the Gagel wind farm in Itzehoe, he came to the conclusion that the maximum sound pressure levels in the infrasound range are far below the perception threshold that is necessary at infrasound frequencies to stimulate the vestibular system. This even applies to people with pathological changes, in which the perception threshold can drop by up to 30 decibels.
With this instrument of the BGR small air pressure fluctuations are measured.
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Image: BGR
The scientists around the environmental engineer Esther Blumendeller, who works in the wind energy department at the University of Stuttgart, came to a similar conclusion. In a study carried out in autumn 2020 in the Swabian Jura, the research team used infrasound microphones to measure low-frequency sound in the range from 1 to 20 Hertz both outdoors and indoors by residents who said they were very annoyed. The four buildings were about one kilometer from the Tegelberg wind farm. In addition, the scientists provided the residents with an app that they could use to report faults caused by the systems immediately. At the time the measurements were taken, three wind turbines were rotating in the park, each with a rated output of 2.78 megawatts. In order to be able to clearly assign certain frequencies to the wind turbines, they were switched off at certain times.