The South Australian EPA has just released a report finding that infrasound – very low frequency sound (between 1 to 20 hertz) – is not noticeably greater in households nearby to wind farms than other locations. It is claimed by some groups and individuals opposed to wind farms, such as the Waubra Foundation, that wind turbines cause a wide array of illnesses to people in nearby residences due to the infrasound they apparently emit.
The report by Resonate Acoustics took measurements of infrasound (dB G) over a period of approximately one week at seven locations in urban areas and four locations in rural areas including two residences approximately 1.5 kilometres away from the wind turbines.
As the report explains, infrasound is not a unique phenomenon associated with wind turbines. Noise generated by people and associated activities within an office space was one of the most significant contributors to measured infrasound levels, with measured infrasound levels typically 10 to 15dB(G) higher when a space was occupied.
Car traffic may also influence the infrasound level in an urban environment, with measured levels during the daytime periods typically 10dB(G) higher than between midnight and 6am, when traffic would be expected to be at its lowest.
At two locations, the EPA offices and an office with a low frequency noise complaint, building air conditioning systems were identified as significant sources of infrasound. These locations exhibited some of the highest levels of infrasound measured during the study.
In rural locations natural wind movements, unrelated to wind turbines, tend to be the main cause of infrasound.
The chart below summarises the study’s results, with the yellow points indicating locations nearby to wind farms. To provide some context for these measurements, infrasound is not easily perceived by the human ear or body but at high levels can create a level of annoyance. According to international noise measurement standards sound pressure levels below 90dB(G) will not normally be significant for human perception, and draft noise guidelines by the Queensland Department of Environment and Resource Management’s recommend an internal noise limit of 85dB(G) for dwellings.
The report concluded from these results:
“It is clear from the results that the infrasound levels measured at the two residential locations near wind farms (Location 8 near the Bluff Wind Farm and Location 9 near Clements Gap Wind Farm) are within the range of infrasound levels measured at comparable locations away from wind farms. Of particular note, the results at one of the houses near a wind farm (Location 8) are the lowest infrasound levels measured at any of the 11 locations included in this study.
“This study concludes that the level of infrasound at houses near the wind turbines assessed is no greater than that experienced in other urban and rural environments, and that the contribution of wind turbines to the measured infrasound levels is insignificant in comparison with the background level of infrasound in the environment.”
It’s worth noting that the study noticed that when wind turbines were shut down for a period of time there was no noticeable reduction in infrasound levels at the houses 1.5 kilometres away.
Also, further additional analysis of the frequency content of the measured infrasound levels was conducted for each location to identify whether wind turbines might lead to an abnormal increase in a particular spectrum of infrasound. The study found peaks in particular frequencies at wind turbine locations,
“were found to be no higher than infrasound levels measured at these frequencies at both rural and urban locations away from wind farms, and also significantly (at least 50dB) lower than the threshold of perception for these very low frequencies.”