via Dan Mills

“Infrasound: Your ears ‘hear’ it but they don’t tell your brain”
—Alec Salt, PhD, Department of Otolaryngology, Washington University School of Medicine, St. Louis, Missouri, USA, at the “Symposium on Adverse Health Effects of Industrial Wind Turbines,” Picton, Ontario, October 29-31, 2010. (See the Cochlear Fluids Research Laboratory site, and “Responses of the Ear to Infrasound and Wind Turbines.”

Highlights:

“Physiologic pathway exists for infrasound at levels that are not heard to affect the brain. The idea that infrasound effects can be dismissed because they are inaudible is incorrect.”

“A-weighted measurements tell you NOTHING about infrasound content.”

“A-weighted spectra totally misrepresent the effects of wind turbine noise (that includes infrasound components) on the ear.”

“A-weighted level readings (e.g., 42 dBA) are totally meaningless for assessing whether turbine noise is affecting the ear.”

Click here to download a PDF of Dr. Salt’s PowerPoint slides, from which the following text was taken.

·
Wind turbines generate infrasound.

Wind turbine infrasound is at levels that cannot be heard.

Widely cited interpretations:

“If you cannot hear a sound … it does not affect you”—Leventhall G. What is infrasound? Progress in Biophysics and Molecular Biology 2007; 93:130–137
“Infrasound is negligible”—DELTA. Low Frequency Noise from Large Wind Turbines 2008
“Infrasound … is below the audible threshold and of no consequence”—Leventhall G. Canadian Acoustics 2006; 34:29-36.
This logic seems to be applied only to hearing. Consider other senses:

Taste: If you can’t taste it, it can’t affect you? Can you taste salmonella?
Smell: If you can’t smell it, it can’t affect you? Try breathing pure CO or CO₂
Sight: If you can’t see it, it can’t affect you? Photokeratitis, “snow blindness”, “welder’s flash”, cataracts, sunburn: Ultraviolet (UV) light is invisible; even though you can’t see it, UV does affect you. UV can harm you.
“If you can’t hear it, it can’t affect you” is only true:

if no other part of the ear is more sensitive than hearing, and
if no other part of the body is more sensitive than hearing …
and I will show this is not true.
Infrasound at moderate levels is detected by the ear.

Infrasound at levels generated by turbines affect the ear.

Vibrations cause a bending of the ear’s sensory hairs. The inner hair cells are connected to auditory (type I) nerve fibers that send signals to the brain. You “hear” with your inner hair cells.

Inner (IHC) and outer (OHC) hair cells respond differently as sound frequency is changed. IHC respond to velocity. OHC respond to displacement. OHC respond at approximately 40 dB below IHC sensitivity at 2 Hz.

Outer hair cells will be stimulated by wind turbine noise. (See graph, below.)



Outer hair cells do not just detect sound:

For low-amplitude high frequencies, OHC elongate when hairs are bent outwards, which makes stimulus greater for IHC (amplifies signal).

Amplifier becomes less effective (less necessary) for higher level sounds, ineffective about 40 dB above threshold (Reichenbach T, Hudspeth AJ. Proc Natl Acad Sci U.S.A. 2010)

High-Frequency stimulus: OHC elongate; Vibration amplitude at the IHC is amplified.

At very low frequencies, we know that bending the hairs laterally causes OHC to contract.

Infrasound stimulus: OHC contract; Vibration amplitude at the IHC is reduced.

OHC are detecting low-level infrasound and actively canceling it for the IHC.

Physiologic pathway exists for infrasound at levels that are not heard to affect the brain. The idea that infrasound effects can be dismissed because they are inaudible is incorrect.

Infrasound => OHC => (via type II nerve fibers) subconscious brain: ear fullness, ear pressure, discomfort, alerting/sleep disturbance

A-weighting corrects a sound measurement to represent what is heard, based on the human audibility (40 phon) curve. At 1 Hz, −148 dB correction, equivalent to dividing by 25 million.

Effect of A-weighting wind turbine noise: Massive (140 dB) de-emphasis of infrasound component. A-weighting may represent what you hear—but hearing does not give a reliable indication of whether the infrasound is affecting your ears.

“A-weighting” principle applied to UV light is equivalent to adjusting sunlight spectrum for what is visible and then saying: “There is nothing here that can harm you. You don’t need sunscreen. You don’t need sunglasses. Go spend all day laying out in the sun.” This approach isn’t rational when applied to light, so why do we accept similar logic applied to sound?

Measuring visible light (e.g., photographs) tells you NOTHING about UV content. Similarly, A-weighted measurements tell you NOTHING about infrasound content.

A-weighted spectra totally misrepresent the effects of wind turbine noise (that includes infrasound components) on the ear.

A-weighted level readings (e.g., 42 dBA) are totally meaningless for assessing whether turbine noise is affecting the ear.

Documenting Wind Turbine Sound

Most video cameras do not record the infrasound component of wind turbine noise.
Speaker systems in TVs and computers cannot play back the infrasound component.
Even if they did—you can’t hear it!
Video recordings of wind turbines give no indication of the infrasound level being produced.
Infrasound can only be measured with specialized instrumentation capable of detecting sounds down to approximately 1 Hz.
G-weighting weights infrasound components (excluding higher frequencies) according to human sensitivity curve.

G-weighted turbine measurements: For most of these conditions, the ear will be stimulated by the turbine noise. (Jakobsen J. Infrasound emission from wind turbines. Journal of Low Frequency Noise Vibration and Active Control 2005; 24:145-155.)

Other ways that infrasound could affect the ear:

Stimulation of vestibular hair cells (saccule, utricle).

Vestibular hair cells are “tuned” to infrasonic frequencies.
No-one has ever measured sensitivity to acoustic infrasound.
Symptoms: unsteadiness, queasiness
Disturbance of inner ear fluids (e.g. endolymph volume).

Low-frequency sound at non-damaging levels induces endolymphatic hydrops (a swelling of one of the fluid spaces).
Infrasound does affect endolymph volume—it is the basis of a treatment for hydrops (Ménière’s disease).
No one has ever measured what level of infrasound causes hydrops.
Symptoms: ear fullness, unsteadiness, tinnitus
Infrasound—affected structures and long-term exposure effects, ranked by sensitivity:

Outer hair cells — “Overworked, tired, irritated” OHC, type II fiber stimulation
Inner ear fluid homeostasis — Volume disturbance, endolymphatic hydrops
Saccular hair cells — Stimulation
Other, non-ear, receptors — Stimulation
Inner hair cells/hearing — None
Sensitivity and sensations remain to be quantified: ear pressure or fullness, discomfort, arousal from sleep; ear fullness, tinnitus, unsteadiness; unsteadiness; stress, anxiety.

“Wind Turbine Syndrome” — You cannot hear what causes the symptoms!

We need more research to define the sensitivity of these processes.

Sounds you cannot hear …

can affect you.
can disturb you.
can harm you.
can cause disease: auditory and balance disorders, effects of sleep deprivation are serious (hypertension, diabetes, mortality).
Conclusion and Recommendations

For years, people have been told that infrasound you cannot hear cannot affect you. This is completely wrong.

Because the inner ear does respond to infrasound at levels that are not heard, people living near wind turbines are being put at risk by infrasound effects on the body that no one presently understands.

Until a scientific understanding of this issue is established we should not be dismissing these effects, but need to be erring on the side of caution.

For industrial turbines a cautious approach could require :

setbacks of at least 2 kilometers (1.25 miles).
in-home monitoring of both A-weighted (audible) and G-weighted (infrasound) noise levels 24 hours/day for all dwellings within 2 miles.
health monitoring studies for those living within 2 miles (with consent).
Finally …

We need to stop ignoring the infrasound component of wind turbine noise and find out why it bothers people!

Wind turbine noise is not comparable to the rustling of leaves.

Protecting the Bats

Court constricts W.Va. wind farm to protect bats
Company must apply for special permit to build more turbines


By Maria Glod
Washington Post Staff Writer
Thursday, December 10, 2009

In a rare green vs. green court case, a federal judge in Maryland has halted expansion of a West Virginia wind farm, saying its massive turbines would kill endangered Indiana bats.

U.S. District Judge Roger W. Titus ruled that Chicago-based Invenergy can complete 40 windmills it has begun to install on an Appalachian ridge in Greenbrier County. But he said the company cannot move forward on the $300 million project -- slated to have 122 turbines along a 23-mile stretch -- without a special permit from the U.S. Fish and Wildlife Service.

"Like death and taxes, there is a virtual certainty that Indiana bats will be harmed, wounded, or killed imminently by the Beech Ridge Project," Titus wrote in a 74-page opinion. "The development of wind energy can and should be encouraged, but wind turbines must be good neighbors."

The lawsuit in Greenbelt is the first court challenge to wind power under the Endangered Species Act, but as wind and solar farms rapidly expand nationwide, similar battles are playing out. Officials and environmentalists are working to find a balance between the benefits of clean energy and the impact on birds, bats and even the water supply.

David Cowan, 72, a longtime caver who fought to stop the project, said the ruling is a victory for the Indiana bat, a brownish-gray creature that weighs about as much as three pennies and, wings outstretched, measures about eight inches. A 2005 estimate concluded that there were 457,000 of them, half as many as in 1967, when they were first listed as endangered. Local populations hibernate in limestone caves within miles of the wind farm.

"I think this is going to make the wind-power people realize that just picking a place that has the right amount of wind isn't all that needs to be looked at," Cowan said.


The court ruled that if it wants to complete the project, Invenergy must seek a federal "incidental take permit," which sets out conditions to mitigate possible harm to an endangered species. The permit, for instance, could restrict the times turbines operate to avoid the bat migration season, bar turbines in the most sensitive areas or require the company to take other steps to protect the bat population.

Until a permit is granted, Titus said, the 40 turbines nearing completion in the first stage of building can operate only in winter, when the bats are hibernating.

Joseph Condo, Invenergy vice president and general counsel, said Invenergy will apply for the permit. He said the completed project would provide power to an estimated 50,000 homes.

"Invenergy continues to be committed to the Beech Ridge project and bringing clean renewable energy to West Virginia," Condo said. "We are very optimistic that the permit will be granted and the project can reach its full potential."

Cowan and other plaintiffs, including the D.C.-based Animal Welfare Institute, support wind power as one way to mitigate climate change. But they say the harm done to the Indiana bat would outweigh the benefits in this instance. The bats, they say, are likely to fly near the turbines in the fall as they migrate to caves from forests, where they spend spring and summer.

Turbines in other locations have killed tens of thousands of bats. Some strike blades. Others die from a condition known as barotrauma, similar to the bends that afflict divers. It occurs when the moving blades create low-pressure zones that cause the bats' tiny lungs to hemorrhage. Scientists and the industry are seeking ways to lessen the number of bats killed, including stopping the turbines at certain times or using sounds to deter the bats.

Invenergy had argued that there is no sign that Indiana bats fly near the ridge. When a consultant put up nets at or near the site in summer 2005 and 2006 to search for bats, no Indiana bats were captured. The company also stressed that there is no confirmed killing of an Indiana bat at any wind farm nationwide.

Eric R. Glitzenstein, an attorney for the plaintiffs, said the lawsuit makes the case for greater federal government oversight of the fast-growing industry that produces wind and solar power. Although coal and nuclear power are regulated, he said, new renewable sources of power are not subject to the same scrutiny.

"This sends an important message that renewable energy is not necessarily green energy," Glitzenstein said. "We should not be creating new ecological crises by addressing existing ones. All energy sources have potential benefits, but they also have potential risks."