Page 34 - Volume 9, Issue 3

cluded that infrasonic weapons were a political distraction from the main points of the disarmament negotiations.
In relation to wind turbines, the concept that “infra- sound is dangerous” has been absorbed into the minds of objectors to wind turbines, who take a one dimensional view of infrasound. That is, they consider only that it may be pres- ent from wind turbines and ignore the very low levels. So we have the connection shown in Fig. 2, which objectors to wind turbines are pleased to believe and which they make use of in planning applications. However, decibel for decibel, infra- sound is less harmful than higher frequency noise.
The Wind Turbine Syndrome
This supposed syndrome is a collection of maladies, said to result from exposure to infrasound from wind turbines, including “... sleep disturbance, headache, tinnitus, ear pres- sure, dizziness, vertigo, nausea, visual blurring, tachycardia, irritability, problems with concentration and memory, and panic episodes associated with sensations of internal pulsa- tion or quivering when awake or asleep.”
In her self-published, popular science book, Nina Pierpont, who practices as a pediatrician, not an acoustics expert, gives two hypotheses on which the wind turbine syn- drome is based.(Pierpont 2009)
1. Wind Turbine Syndrome, I propose, is mediated by the vestibular system — by disturbed sensory input to eyes, inner ears, and stretch and pressure receptors in a variety of body locations. These feed back neurolog- ically onto a person’s sense of position and motion in space, which is in turn connected in multiple ways to brain functions as disparate as spatial memory and anxiety ...
2. Air pressure fluctuations in the range of 4-8 Hz, which may be harmonics of the turbine blade-passing frequency, may resonate (amplify) in the chest and be felt as vibrations or quivering of the diaphragm with its attached abdominal organ mass (liver). Slower air pressure fluctuations, which could be the blade-pass- ing frequencies themselves or a lower harmonic (1-2 Hz), would be felt as pulsations as opposed to the faster vibrations or quivering ... The pressure fluctu- ations in the chest could disturb visceral receptors, such as large vessel or pulmonary baroreceptors or mediastinal stretch receptors which function as vis- ceral graviceptors.These aberrant signals from the vis- ceral graviceptors, not concordant with signals from the other parts of the motion-detecting system, have the potential to activate the integrated neural net- works that link motion detection with somatic and autonomic outflow, emotional fear responses, and aversive learning.
To summarize, Pierpont’s claim is that the low levels of infra- sound from wind turbines have a direct pathophysiological effect on the body, through the vestibular systems and also by excitation of the airways and diaphragm to the viscera. However, she has little understanding of acoustic magnitudes and changes at will between noise and vibration. The scien- tific backing for Hypothesis 1 is a paper on vestibular detec-
tion of vibration applied to the mastoid bone. In adopting this she has misrepresented the original paper (Todd, Rosengren et al. 2008) as being based on excitation by noise, when it was actually a bone conducted vibration detection investigation, comparing thresholds of vestibular and cochlear detection. Following a newspaper item which con- nected him with the wind turbine syndrome, Todd repudiat- ed Pierpont’s use of his work (Todd 2009). The backing for Hypothesis 2 is in body resonances resulting from whole body vibration. However, excitation by point vibration input at the seat or feet differs from that for long wavelength sound, which acts over the whole body, and different resonances are excited. Pierpont’s hypotheses are scientifically invalid.
Some people are distressed by wind turbines, and noise is a factor in this. Those at the sharp end of environmental noise problems know how upsetting noise can become, espe- cially if there is an antagonism towards the source. Symptoms which are given by Pierpont as comprising the Wind Turbine Syndrome are paralleled in the extreme distress from any environmental noise, which occurs with a small number of people, especially when coupled with psychological factors. However, Pierpont dismisses psychological effects with, “It is important to emphasize, these symptoms are not psycholog- ical (as if people are fabricating them), they are neurological.” This contradicts much of what is known about responses to noise, especially low level noise. (Job 1988, Miedema and Vos 1999).
Pierpont has been the main proponent of dangers of infrasound from wind turbines and she, along with those who follow her, is responsible for much of the present public attitude. A fuller critique of Pierpont’s work has been given previously (Leventhall 2009).
Support for an adverse effect from wind turbine infra- sound has been given by Salt and Hullar, who showed that, at 5Hz, the outer hair cell (OHC) response threshold in guinea pigs is lower than the guinea pig hearing threshold, which depends on inner hair cell excitation. (Salt and Hullar 2010). This led to the definition of a rather broad brush OHC threshold, which gradually diverges from the hearing thresh- old below 1000Hz. Comparison of guinea pig and human hearing thresholds was used to define an equivalent OHC threshold for humans. The final destination in the brain of the excitations from the OHCs, which are not transmitted along the auditory nerve, is not known. Salt is cautious in his scientific papers and writes “The fact that some inner ear components (such as the OHC) may respond to infrasound at the frequencies and levels generated by wind turbines does not necessarily mean that they will be perceived or disturb function in any way.” (Salt and Hullar 2010). However, Salt’s web page falls squarely in the “infrasound is hazardous” school (<http://oto2.wustl.edu/cochlea/wind.html>).
The proposed inner and outer hair cell thresholds for humans are compared in Fig. 3. The outer hair cell threshold is 20dB at 100Hz, rising at 40dB/decade into lower frequen- cies, crossing 60dB at 10Hz and 100dB at 1Hz. The next sec- tion covers infrasound from wind turbines and it will be noted that much of this infrasound, especially at lower infra- sound frequencies, is below the outer hair cell threshold, so
Concerns About Infrasound from Wind Turbines 33