Hessler, George Comments to South Australian EPA re Study at Waterloo Wind Farm
George Hessler, Hessler Associated, Inc.
February 28, 2014
No one knows why a relatively few wind farms evoke such intense adverse community reaction with multiple claims of ill health effects. Two wind farms of recent notoriety in this regard are the Waterloo project in Southern Australia and the Shirley wind farm in the United States.
Anti-wind farm advocates contend that low frequency infrasound (0 to 20 Hz frequency range) is the cause of ill health effects, but cannot explain why the overwhelming vast majority of wind farms operate successfully and do not elicit any adverse community response. Similarly, pro-wind farm advocates cannot explain the reaction at sites like Waterloo and Shirley.
The EPA measurement program at Waterloo showed similar results as at Shirley that there is a measurable low level of infrasound that reaches a maximum level around the blade passing frequency (BPF) and harmonics of the wind turbines. Three bladed modern wind turbines rotate in the 10 to 14 RPM range so the BPF ranges from 0.5 to 0.7 Hz or period of 2 to 1.4 seconds. At these very low and slow frequencies and periods, any such sound pressure would be perceived, if at all, as a series of pulses, not as ordinary noise.
The threshold for hearing for ordinary low frequency noise is currently standardized down to only 20 Hz, far far above the frequency of maximum infrasound generated by wind turbines.
Published thresholds below 20Hz down to 4 Hz are fairly uniform between researchers with a scatter band of results of approximately 9dB. Research below 4 Hz is sparse and variances between the few researchers reach 20 dB.