HGC Engineering was retained by the Ontario Ministry of the Environment (MOE) to provide an Expert Report that featured a literature review of materials related to low frequency noise and infrasound associated with large, modern, upwind wind turbine generators. One important aspect of the review was examining the potential health effects of exposure to wind turbines from an acoustical perpective. Materials researched and referenced included journal articles, papers presented at technical conferences, technical reports, as well as guidelines or regulations from various jurisdictions were reviewed.
The review of related assessment standards used in different jurisdictions showed that some countries have developed guidelines which generically address low frequency noise and infrasound. At this time, it is not common for international wind turbine noise assessment standards to have specific requirements for the consideration of infrasound or low frequency noise, with the exception that many standards explicitly consider and penalize tones, which when present tend to be in the low frequency range.
Because associated fields of study are relatively new, and research is ongoing, we recommended that the MOE continue to monitor technical developments in this area and keep abreast of regulatory policies that may be introduced in other jurisdictions.”There are aspects of infrasound from wind turbines that are not unanimously accepted by all technical and medical practitioners and there remains a degree of public apprehension associated with infrasound.”
Complaints of low frequency noise described in the literature are commonly related to indoor noise. The measurement of indoor low frequency noise is complicated by a number of factors. Internationally, sophisticated measurement and assessment guidelines have been developed to address these problems in recent years. Since it is evident that complaints related to low frequency noise from wind turbines often arise from the characteristics of the sound impact indoors, and since the indoor low frequency sound levels and frequency spectra can differ markedly from those outdoors, we recommended that the MOE consider developing or adopting a protocol to provide guidance for addressing indoor complaints. Given the large variation in indoor sound impact resulting as a function of room layout and sound transmission characteristics, this protocol cannot replace the current compliance guidelines designed to assess sound outdoor.
One of our key conclusions was that Infrasound from wind turbines is not expected to be heard by humans or pose an issue for human health, and as such, routine measurement of infrasonic sound pressure levels from operating wind farms was not warranted to the same degree that the measurement and monitoring of overall A-weighted sound pressure levels are. Nonetheless, there are aspects of infrasound from wind turbines that are not unanimously accepted by all technical and medical practitioners and there remains a degree of public apprehension associated with infrasound. It was therefore recommended that the MOE consider adopting or endorsing measurement procedures described in the literature that could be used to quantify the infrasonic levels in specific situations.