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Low Frequency Noise and Infrasound  

Author:  | Noise, Regulations, U.K., Wildlife

This literary report [which was submitted to the U.K. Dept. of Trade and Industry] has combined a variety of study findings and concludes there is a case to answer when land based animals and freshwater creatures are exposed to noise at low Hz levels. [Appendix B is a table of creatures, from alligators to whales, and the documented effects of noise exposure.]

Because of the limitations of our hearing it would be easy to suppose that noises beyond our receiving range do not exist and should therefore be of no concern to us. Yet both very high and extremely low inaudible sounds may be harmful to us and other animals with similar but not identical ranges of hearing.

Different people perceive sounds differently and much depends upon the individual levels of tolerance and what to them constitutes disturbance. Other creatures have lower acceptance levels, as their survival is more reliant upon instinct and interpretation of unusual sounds as a source of danger. …

To gauge effect of LFN [low frequency noise] and infrasound upon land based and freshwater creatures then concentration should be focussed upon intensity and frequency as much as upon speed of travel. Sound travels faster in a mass of greater density than air. Therefore a greater pressure level is also delivered suggesting a perturbing situation might exist for both freshwater dwellers and land based creatures diving under freshwater water in close proximity to sound sources emitting high intensity LFN over long periods of time.

Sources of infrasound and LFN are many and varied with constant new additions. Some are controversial for reasons including noise emissions. Wind turbine generators were raised as a noise concern some years ago. Yet only recently have reports been released by the wind industry with results of desktop studies and none seem to have been conducted on wild animals at wind farms.

A UK press release in 2005 suggested blame for the death of baby seals was due to mother seals aborting their pups through disturbance from pile driving for foundations for off shore wind turbines. Elsewhere some studies have shown that sea mammals, fish, birds and animals exposed to excessive LFN and infrasound has caused them harm. …

Whales, dolphins and porpoise have all shown signs of distress from exposure to varying levels of noise at low frequencies and from a variety of sources. Research has shown fish ears are damaged by noise from repeated use of under water air guns and behavioural studies determined the fish became disoriented and consequently were vulnerable.

There are a great number of articles that include reference to the effects of infrasound upon humans. The frequency ranges are recorded in many of these and the overall result always appears to depend upon the exposure time when coupled with the dB and Hz levels.

A few seconds is all it takes at very low Hz and high dB levels before severe problems arise. Even at a level of dB normally found comfortable for listening to music for example, if the Hz level is low then a significant adverse reaction has been reported.

There is reason to suppose that similar effects would also occur with wild animals if exposed to the sounds for long enough periods. The presumption must be that as soon as they felt uncomfortable they would move away from the zone of discomfort. A term more properly described as, disturbance and displacement, which in the case of protected species would be contrary to appropriate legislation.

The concerns of the effects of infrasound are clearly real whether they are upon humans, marine life or land based and freshwater creatures and in extreme cases the results of high levels of exposure could be lethal. Even relatively low levels can be debilitating and create disturbance. …

Other experiments signify that indirect consequences can arise from exposure to LFN due to the masking effect. Sounds from wind turbines are believed to have disguised the danger of rotating blades and caused the death of large numbers of birds. A report concluded that birds probably couldn’t hear the noise of the blades as well as humans can and would be unable to see them because of motion smear.

Constant road noise raises the ambient levels and could affect creatures because of the masking effect. Less frequent but regular sounds might create just enough habituation as to be dangerous and occasionally (such as in country lanes) lull creatures from hiding at lethal moments.

Estimates have been made that bird song will attenuate at the rate of 5dB per metre for a bird 10metres above ground level in an open field to 20dB per metre for a bird on the ground in a coniferous forest. Therefore any high volume of noise of a virtually permanent rate, such as continuous nearby traffic flow could mask communication attempts.

Studies have been made of the effects of noise upon some bird species and quite clearly low frequency noise played a significant role in creating bird disturbance/displacement and was sufficient to cause serious reduction in breeding numbers in the study areas.

Vocal communication plays an important part in the social interaction of many creatures and the imposition of noise from man-made sources could potentially disrupt the ability of species to communicate or it might introduce new and possibly disturbing behavioural factors into social groups. …

Recorded noise from a miscellany of sources including machinery, military hardware, electrical and diesel engines, roller coasters and many others have been used in experiments upon sheep and lambs and the results have shown increased heart rates, respiratory changes and reduction in feeding.

Anthropological sources of LFN and infrasound are increasing and will continue so to do. There is clearly a cause for concern because of the likely effects upon wildlife and current protective measures seem inadequate.

Thus it is recommended that better environmental assessments be made to accompany all planning applications involving erection or construction of plant, machinery, buildings, infrastructure or other potential sources of low frequency noise and infrasound, irrespective of project size.

The measurement methods should be reviewed to embrace “˜C’ Weighting and “˜G’ Weighting as well as the usual “˜A’ Weighting so that a proper appreciation of the extent of LFN and infrasound is achieved before, during and after the noise source is installed.

Moreover, regarding larger sites continuous wildlife monitoring and reporting should be in place with conditions attached to planning consents that an order for immediate cessation of the noise source can be made without the need for further deliberation if found detrimental to creature well being.

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This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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