Doolan, Assoc Prof Con. Expert Review, NHMRC Draft Information Paper

Associate Professor Con Doolan
School of Mechanical Engineering
The University of Adelaide, SA, 5005

April 4, 2014


This document is a review of the NHMRC Draft Information Paper: Evidence on Wind Farms and Human Health. It is written from the perspective of the field of expertise of the reviewer (aeroacoustics) and specifically considers the points posed by the NHMRC. These points are addressed in three separate sections below with a fourth dedicated to some additional comments by the reviewer.

The rationale applied in examining the evidence on the potential health effects of wind turbine (sic) is understandable and clearly explained

I believe the rationale is clearly explained and is broadly acceptable. One area that I believe can be approved is the critical appraisal (§3.4). It is uncertain whether the criticisms are based on professional opinion, some analysis, or both. If the criticisms of some studies are the opinions of the authors (reached in the absence of further analysis), then that should be clearly stated. If the criticisms have some analytical or other basis, then similarly these need to be stated in the paper. 

The evidence has been accurately translated into the messages in the Draft Information Paper

In §7.4, this statement is made: “It is unlikely that substantial wind farm noise would be heard at distances of more than 500–1500 m from wind farms. Noise levels vary with terrain, type of turbines and weather conditions.” The statement is vague in one way, yet a little too prescriptive in another, which may lead to confusion. It is true that wind turbine noise sound pressure level decreases with distance form the turbine tower, but how do you define “substantial”? The actual level will depend on the size and power output of the turbine, wind farm design as well as the meteorological conditions the turbines are operating in. It also depends on the noise sensitivity of the individual. What I think this points to is a lack of reference to the reasons for the existing environmental noise regulations for wind turbines in this report. These regulations (such as the South Australian EPA guidelines) describe noise limits for wind farms. I suggest that these limits, as regulated, can be used to better define what is meant by “substantial noise” in this report. It should be noted that most regulations need improving to include the effects of low-frequency noise, amplitude modulation and tonality, but nevertheless, they are the regulations at the moment.

This brings me to another point. It is not very clearly stated in the report that wind turbines are noise generators with significant sound power. One may get the impression that they don’t produce significant noise at all. However, it is already recognised that noise generated by them is significant enough to be regulated by governments to protect the amenity of communities and prevent unwanted noise pollution. In fact, noise from turbines significantly affects the number of turbines that can be placed in a farm, limiting their profitability. I think the report needs to recognise more clearly that the sound power of wind turbines is significant enough to be regulated by governments to ensure the protection of communities from environmental noise pollution.

The following statement is not accurate and must be changed (§7.2.2, referring to the effect of environmental noise on health, in general): “Associations between noise exposure and some other health conditions (including high blood pressure, heart attack and depression) have also been suggested, but these associations are based on limited evidence 19.

First, Reference 19 is not an appropriate reference to support this statement. Second, the World Health Organisation (as reported in Reference 21 in the NHMRC report) concludes: 

There is sufficient evidence from large-scale epidemiological studies linking the population’s exposure to environmental noise with adverse health effects. Therefore, environmental noise should be considered not only as a cause of nuisance but also a concern for public health and environmental health.

I am sure the authors of the NHMRC report do not mean to contradict the World Health Organisation (WHO) and many decades of study linking environ- mental noise pollution with health. Please change the statement or delete it.

Further, please carefully consider the statement in the same section, referring to the effect of environmental noise (from all sources) on sleep disturbance: “However even in the worst cases, the effects are modest”. The WHO (cited as Ref 21 in the NHMRC report) calculate that in Europe alone, the burden of disease sustained by noise-induced sleep disturbance is enormous. There are many other studies that show and warn of the very serious health effects of noise-induced sleep disturbance, as well as other health impacts (as mentioned above). As this document is aimed at informing the public and policy makers, the last thing I would want to see is an incorrect opinion formed in the public mind regarding environmental noise pollution and its effect on health. The statement on health effects of sleep disturbance goes beyond the original scope of the report in that it extends the discussion to all forms of noise, when it should be limited to noise from wind turbines. Hence the statement must be corrected. 

The conclusions in the documents align with your understanding of the latest evidence in your area of expertise

I broadly agree with the conclusions made in §7.2.3; however, there are some points that need discussion and/or improvement. The statements made earlier in the report (and discussed above in this review) give the impression that the effects of environmental noise pollution from all sources (aircraft, rail, road, etc) are unimportant or have an inconclusive effect on health, which is not true. This impression or style seems to have percolated into the concise conclusions of §7.2.3. The emphasis appears to be on negating claims already made concerning wind turbine noise, when it could equally be concluded that the the existing evidence is poor and more work is needed to obtain better quality data. Indeed, the NHMRC report does suggest this in an appendix, but I feel that the inconclusive nature of the existing body of literature needs to be stated in a more balanced manner in §7.2.3 (as it may be the only section a busy policy maker will read) with a direct reference to a requirement for new research. 

Other comments

  1. An executive summary or abstract should be at the beginning of the report.
  2. In §1.2, please rewrite: “Wind turbines are towers with rotating blades that harness wind to produce electricity.”, to read: “Wind turbines use rotating blades attached to towers in order to convert wind energy into electricity.”
  3. I have a few problems with this statement that appears on page 12:

“Wind turbines produce mechanical sound at a frequency of 20–30 Hertz (for a 1500 kilowatt turbine)2 and a “whooshing” aerodynamic sound in the rangeof 200–1000 Hertz33,34. Noise from wind farms is mostly aerodynamic8,9,35”

In my opinion, these statements are too definitive and the references used are not suitable to support these statements. While it is true that wind turbines may produce mechanical noise at low-frequency, whooshing noise can be produced below 200 Hz and above 1000 Hz. Two well known aerodynamic noise mechanisms are responsible. In-flow turbulence (from the atmospheric boundary layer or other sources) can create lower frequency sound, certainly below 200 Hz and quite probably up to 1000 Hz and above. Further, turbulent trailing edge interaction noise can be produced from low frequencies (the lower limit has not been determined, but would likely be below 200 Hz) to well above 1000 Hz. I recommend that the references listed below be used to provide a more accurate statement. Another (infrasonic) source mechanism – thickness noise – is not mentioned at all. Any rotating blade will create thickness noise at the rotational frequency. While the infrasonic source strength may be very low (as supported by the evidence), I would think it is only fair to inform the reader that infrasonic sources do exist on a turbine.

Grosveld, Ferdinand W. “Prediction of broadband noise from horizontal axis wind turbines.” Journal of propulsion and power, 1(4) (1985): 292-299.

Wagner, S. Wind Turbine Noise. Springer Berlin Heidelberg, 1996.

Oerlemans, Stefan, P. Sijtsma, and B. Mndez Lpez. “Location and quantification of noise sources on a wind turbine.” Journal of sound and vibration 299(4) (2007): 869-883.

Glegg, S. A. L., S. M. Baxter, and A. G. Glendinning. “The prediction of broadband noise from wind turbines.” Journal of sound and vibration 118(2) (1987): 217-239.

  1. Please change the definition “Aerodynamic sound: For wind turbines, the sound generated by the interaction of the blade trailing edge, tip or surface with air turbulence.” to:

“Aerodynamic sound: For wind turbines, the sound generated by the interaction of the blade trailing edge, tip or surface with turbulent air flow.”

In my opinion this is more precise. “Air turbulence” may be interpreted to apply to atmospheric turbulence only, where wind turbine noise is generated by more forms of turbulence than that.

  1. The definition of decibel: “Decibel: A unit of measure used to express the loudness of sound, calculated as the logarithmic ratio of sound pressure level against a reference pressure.” needs improving. Loundness is measured in another unit (Phon), Decibels is a standard way to express any measurement in a logarithmic scale, while Sound Pressure Level in Decibels is a unit of measure to express sound pressure level only, calculated as the logarithmic ratio of sound pressure level against a reference pressure, multiplied by 20.

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