When I was eight years old, I was on the verge of being eaten. Terrified, I buried myself underneath the blankets, and nervously listened to an unearthly howling directly outside my bedroom window. I realised soon that the noise I had heard was the wind passing through the eaves of my family’s aged London terrace house, a noise that had sounded eerily sentient. My fear was simply related to a lack of data – those few extra seconds of dogged listening eased my concerns. We are evolutionarily wired towards the sensation of threat – a sensation that is overridden by taking time to pause, and listen closely.

Objections to the installation of wind farms have, in the past four years, played on this aspect of our nature. Claims have arisen that inaudible, infrasonic noise emissions have a direct effect of human physiology, bypassing our conscious percept and wreaking biological devastation. For this hypothesis to hold true, two basic principles need to be demonstrated conclusively:

– Infrasound emitted from wind farms has to be markedly higher in amplitude than infrasound produced by other sources;

– This amplitude has to be causally linked to a direct and demonstrable pathological effect on human physiology.

The South Australian Environmental Protection Agency (SA EPA) recently took some time to investigate the first premise: that wind farm infrasound measures higher than that from other sources in the environment. If the premise were found to be true, then wind turbine syndrome might well be a reality. If it were found to be false, then it serves as firm evidence that ‘wind turbine syndrome’ is deeply improbable.

The Salt Hypothesis

Alec Salt, a professor at the Washington University School of Medicine, has formulated a theory, regarding the response of the human ear to varying levels of infrasound – the second of our two hypothetical requirements. Salt suspects the outer hair cells (OHCs) of the human ear produce a response, when subjected to a certain infrasound stimulus, and tested his theory with the in-vitro OHCs of guinea pigs.

Importantly, his work focuses on amplitude – specifically, he nominates 60 dB(G) as the trigger value for the OHCs to begin their ‘physiologic reaction’- the response championed by opponents of wind developments as the primary cause of ‘wind turbine syndrome’. If this amplitude were discovered to be unique to wind farms, it would be a vindication for those calling for a moratorium on wind energy.

The EPA Discussion

The authors of the EPA paper are unequivocal in their consideration of infrasound:

“The key effect of infrasound can be a high level of annoyance when the level exceeds the hearing threshold, i.e. it must be perceptible to have an effect. No physiological effects have been found to occur below the level of perceptibility.”

Infrasound can actually be perceived, once it reaches a certain amplitude. This threshold increases as you move down the frequency range, towards zero. The authors propose a conservative criterion of 85 dB(G), based on several different assessment criteria. Importantly, this accounts for individual differences in perception thresholds for infrasound.

They use the ‘G-weighting’, a mathematical tool for ensuring that absolute measurements of sound pressure level are adjusted for the way the human body responds to sound in the infrasonic range. This what the ‘(G)’ means in ‘dB(G)’. The Australian Acoustical Society consider this weighting to be appropriate as per international standards, as they assert in an unpublished letter to The Australian.

Infrasound Measurements – Urban Locations

The EPA, in conjunction with Resonate Acoustics, reported on the levels of infrasound at various locations in urban locales (four offices and three residences).

One important finding is that the presence of human beings is a significant source of infrasound. The authors state, with regards to Location 1 (an office on Carrington St):

“The primary factor affecting the measured infrasound levels at Location 1 appears to be occupation of the office, as evidenced by the marked rise in the measured levels at approximately 4pm on Saturday and 2pm on Sunday when staff were noted to enter the office.”

The same conclusion was reached for Location 6, a house in Firle – human activity seems to be a demonstrable and significant contributor to the generation of infrasonic sound emissions.

Another important finding is the significant contribution of air-conditioning units to measured infrasound levels. Location 3, the EPA office in Adelaide exhibited “some of the highest levels measured at any of the urban and rural locations”. Traffic also resulted in infrasound levels that were “10 to 15dB(G) higher than that at night time”.

These are major problems for groups that claim infrasound has an as-yet undiscovered toxicity for the human body, at levels above 60 dB(G). There are 22,917,973 humans and 16,741,664 cars in Australia. Two-thirds of dwellings own some form of cooling – that’s around 7.6m x (2/3) = 5,066,000 air conditioner units. This means there are roughly 44.7 million unique sources of infrasound in Australia.

Infrasound Measurements – Rural environments

Wind farms are almost always placed in rural environments. The EPA measured the infrasound levels in four different locations that were host to a wind farm. Wind farm shutdowns were used to determine the contribution of the wind farm to infrasound levels at these locations. Their findings are unremarkable.

It would seem that the wind farms do not contribute significantly to measured infrasound level in rural dwellings – during the shutdown of the Bluff wind farm, the measured infrasound actually increased.

Distance has long been a creative component of the anti-wind lobby’s claims. Sarah Laurie has stated that “residents report the effects of the low frequency noise out to 10km”, but also offers 30 kilometres as the effective range of ‘wind turbine syndrome’. Motivated anti-wind enthusiast George Papadopoulos claims it can be perceived up to 100 kilometres away from wind turbines.

The EPA measured levels at a house 10 kilometres away from an operational wind turbine and found that “infrasound levels at the house are not related to wind farm operation, but rather are representative of the ambient infrasound environment at the farmhouse”.

They also measured infrasound levels at a house 30 kilometres away from a wind turbine. They simply concluded that “local wind speed (and localised turbulence) is a primary cause of infrasound levels at a location, and have a similar effect on both outdoor and indoor levels of infrasound”.

Frequency Analysis

The EPA also use their data to look at specific frequencies in the infrasonic range, between 0.25 Hz and 20 Hz (the previous sections present ‘measured infrasound’ as a single dB(G) value, over time). They do not use the G-weighting in this section. Their conclusions are similar.

“The results suggests that indoor infrasound levels at rural residences near to wind farms are no higher than those at rural residences away from wind farms, nor than infrasound levels at residences within urban areas.”

“There is minimal contribution from either the Bluff Wind Farm or the Clements Gap Wind Farm to sound pressure levels in the infrasonic region at the houses located approximately 1.5 kilometres away.”

Location 8, 1.5 kilometres away from the nearest wind turbine, showed ‘the lowest infrasound levels measured at any of the 11 locations included in this study.’

Interestingly, they did find some curious results when examining the contribution of the wind farm to low-level peaks that occur when the blades pass the tower, though they note, “sound pressure levels at these blade pass frequencies are no greater at residences adjacent to wind farms than at other locations”.

The Aftermath

The EPA’s conclusion is simple:

“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 is also significantly below the human perception threshold.”

This study is important, but not revelatory. The logical consequence of these findings, the anti-wind lobby are correct in their assertions, is that wind farms, human beings, traffic, air-conditioners and the wind itself are constantly triggering our outer hair cells, resulting in a catastrophic and constant worldwide apocalypse. There is no refuge from the dangers they preach – wind turbine syndrome is everywhere, or it is nowhere.

On the February 4 this year, Radio National’s Timothy McDonald interviewed Sarah Laurie about the research. Laurie asserts the following:

“The report itself, the authors only measured down to 10 hertz by using what we call the G-weighting. They ignored the frequencies between 0 and 10 hertz. And they’re the frequencies that many of us believe are the problem frequencies. So they didn’t actually measure those.”

As we saw earlier, the authors of the report measured down to 0.25 Hz. They state this range on 20 separate occasions in the report. Additionally, there seems to be no evidence of Laurie’s assertion that she is mainly concerned with frequencies between 0-10 Hz prior to the release of the EPA study (she states ‘0 – 200 Hz’ as the frequency range of greatest concern to the Waubra Foundation here, and makes a similar assertion in a letter to Prime Minister Julia Gillard, here).

Another curious response is the claim that the authors ought to have used linear, un-weighted measurements, rather than the G-weighting (presented amongst the wretchedly unpleasant sneer ‘Clean Energy Stasi’). This claim would presumably not sit well with Dr. Alec Salt, who unambiguously demands infrasound measurements utilise the G-weighting.

Regardless, the EPA included un-weighted measurements of sound pressure level (dB) across the infrasonic frequency range as part of their ‘Frequency Analysis’ section – see the figure below for an example, taken from page 57.

These responses seem to be free of logic or rigour. This is no hindrance for a movement that is borne of anger, emotion and excess rather than rationality. Where we ought to see logic, we see manic, frothing comparisons to genocidal regimes, peppered with unchecked falsehoods.

After nearly three years of heatedly calling for more research into the health effects of wind turbines, the anti-wind lobby may well consider being careful what they wish for. The Waterloo Wind Farm in South Australia is currently the subject of a similar study by the EPA, determining the levels of infrasound at nearby residences attributable to the wind farm.

Anonymous, cruel-tongued anti-wind bloggers and tabloid current affairs shows have already declared the mere commencement of this study as undeniable proof of a problem with wind energy – a logical fallacy that neatly summarises their loathsome, love-hate relationship with scientific inquiry.

For many centuries, areas untouched by empirical investigation have proven rich, fertile ground for spreading fear and anxiety. A deficiency in evidence has often been obscured by emotion, noise and anecdote. As our knowledge grows, those who dwell nervously in these dark spaces find themselves cramped and uncomfortable.

Ketan Joshi is a research and communications officer at Infigen Energy