’Common Concerns about Wind Power’ report
Second edition coming soon ...
2 October 2014
CSE is in the process of updating the popular report 'Common Concerns about Wind Power' that we first published in 2011. The second edition is expected to be published in 2015.
The report, which has been downloaded from this website around 25,000 times, draws on peer-reviewed articles and research to examine a range of issues including: efficiency, energy payback times, subsidies, shadow flicker and epilepsy, noise, bat and bird mortality, and effects on property prices.
It was originally written in response to requests from community groups for factual information about wind power, and, in addition to the downloads, around 10,000 printed copies have been distributed.
We're obviously interested in new research, and so unsurprisingly our attention was drawn to an article in the Telegraph on 1 October headlined 'Living close to wind farms could cause hearing damage' (and the Daily Mail's 'Could living near a wind farm make you DEAF?'). It based this claim on research published by the Royal Society entitled 'Low-frequency sound affects active micromechanics in the human inner ear' so we asked our lead author Iain Cox to examine this research paper and see if it was relevant for our updated report.
This is Iain's response (and, yes, it's quite technical).
“I had a quick look at the Drexl paper. One can’t help but feel the Telegraph article manufactures a tenuous link with wind power, since the research paper doesn't mention wind turbines at all.
“The low-frequency sound level used by the Drexl group was 30 Hz at 80 dB(A), which is within the normal audible threshold for humans. However, at 500 m separation distance a wind turbine (even a large >2 MW turbine) would produce a sound pressure wave at 30 Hz of around 45–50 dB(A). This is still audible, but it is lower than road traffic noise at similar frequencies, which is around 55 dB(A).
“The otoacoustic emissions (OAEs) described in the Drexl paper have been known for a long time, at least since the late 1970s, and are a reflection of the fact that the ear is a two-way acoustic system, so that vibrations of the outer hair cells in the cochlea (the inner ear) are transmitted back to the ear drum, and these vibrations of the ear drum can be measured using a microphone placed in the ear canal to give an insight into normal cochlear function. This is essentially the method the Drexl group use. It is thought that OAEs are a by-product of the inner ear's mechanism for improved hearing resolution, known as the 'cochlear amplifier'. The fluid in the inner ear is actually quite good at attenuating feedback at higher frequencies, but it does allow low-frequency and infrasound frequencies through. (Note infrasound is below the audible threshold unless the sound pressure levels are very high.) Indeed, such is the feedback at frequencies below the audible range that detections of infrasound pulses from external sources (like wind turbines) are typically swamped from the internal infrasound the ear experiences from the subject's own heartbeat or breathing!
“What the Drexl study shows is that exposure to LF noise of 30 Hz for 90 seconds induced a change in the active cochlear mechanism, as measured through the proxy of spontaneous OAEs, that lasted for almost two minutes after the noise exposure stopped (i.e. the altered pattern of OAEs lasted 100 seconds before disappearing). The authors suggest that since the 80 dB(A) level is below many occupation-related exposure safety thresholds that this warrants further investigation, since persons subjected to these noise levels for extended periods may experience a transient alteration of their active cochlear mechanism that lasts for a significant period after the exposure has stopped. However, they do not know whether these alterations are an indicator of the start of a damaging process in the cochlea - that would be just a speculation.
“That's it. The study did not look into whether there was actual damage caused to the ear or not. And how this relates to residents near wind farms is not clear, since normal separation distances mean that residents will be exposed to much lower sound levels at these low frequencies, where other sources of LF noise – like traffic, or even the sound of surf crashing for people near the coast – are greater. I notice the Telegraph is not advocating we ban cars or, for that matter, the sea.”
We also received this comment from Peter Brown FRCS, a retired ENT surgeon:
"All the Munich paper is saying is that LF sound, even though barely heard, stimulates more Otoaccoustic Emissions that expected - so what? They are not an indicator of cochlear damage. A 'Temporary Threshold Shift' would indicate a risk of damage and is usually related to amplitude and duration of the noise exposure. They have not correlated LF emissions to hair cell damage and this was not a part of the study."
Iain and Peter weren't the only ones who were surprised to find that the research paper by Drexl et al didn't mention wind turbines, as the Twitter exchange below shows: