Infrasound and Low Frequency

II. Infrasound and low frequency noise from wind turbines: exposure and health effects

The increase in use of wind power as an energy source in recent years has raised concerns of health issues related to the low frequency noise (LFN) and infrasound emitted by wind turbines. It is a concern that as wind turbines increase in size, the sound characteristics will shift to lower frequencies. Sounds with components of low frequency sound and infrasound may have more serious affects on human health than sounds without these components. Prolonged exposure may result in symptoms such as headaches, stress, and sleep disturbance. LFN is defined as frequencies between 20 and 200 Hz and infrasound is sound frequencies between 1 and 20 Hz.

Sound production and exposure

The main source of noise produced by wind turbines is created by aerodynamic sources at the blades. Depending on how the noise is made, different frequencies are produced. Periodic blade-tower interaction creates frequencies between 1 and 30 Hz, trailing edge noise creates peak frequencies between 500 and 1000 Hz, and the in-flow turbulence creates the majority of noise frequencies between 10 to a few hundred Hz.

The average noise guideline for wind turbine noise is usually around 40 dB. The average regulation on road traffic noise at the façade of dwellings, found among fourteen European countries, was 55 dB. These sound levels were compared and it was found that, “LFN from wind turbines does not generate more LFN than road traffic noise at levels often found in urban residential areas.”

Noise Annoyance

There have been several studies done on levels of annoyance from wind turbine noise. Questionnaires were given on what noises are most annoying when heard outside of the individual’s home, followed by a list of noises including turbine noise. When wind turbine noise guidelines of around 40 dB are adhered to, the number of people that are annoyed is similar to the number of people irritated by road traffic. However, at equivalent sound levels wind turbine noise is found to be more agitating. There are three possible explanations for this annoyance: 1) Wind turbines are built in areas with low ambient noise, 2) Wind turbine noise has a “swishing” characteristic, and 3) The visual intrusion of wind turbines can further annoyance overall.

Sleep Disturbance

Sleep is an essential part of good health. Most studies done on the relationship between wind turbine noise and sleep disturbance only include self-reported sleep disturbance, which is not an accurate indication of any correlation. Wind turbine noise may be louder at night because of the more stable atmospheric conditions, causing sleep disturbance in some cases. One issue with this is that there is no standard way to measure wind turbine noise.

Other health effects

‘The Wind Turbine Syndrome’ by Nina Pierpont discusses health problems associated with wind turbine noise. However, her research was based on interviews and contained no acoustic measurements, no contact with subjects prior to complaints to assess their health, and was a very small sample group. Another proposed health issue is ‘vibro-acoustic disease’. This includes symptoms such as cardiovascular effects. It is thought that this is only a problem in high occupational exposures, such as aircraft maintenance. There has not been enough research done to assess the correlation between wind turbine noise and cardiovascular problems. However, some correlation between aircraft noise, road traffic, and elevated blood pressure has been seen. Therefore, if wind turbine noise is causing annoyance and sleep disturbance, it cannot be ruled out that with prolonged exposure to wind turbine noise there may be effects on the cardiovascular system.

Bolin, K., Bluhm, G., Eriksson, G., & Nilsson, M. (2011). Infrasound and low frequency noise from  wind turbines: exposure and health effects. Environmental Research Letters, 6(3), Retrieved from http://iopscience.iop.org/1748-9326/6/3/035103