Mr. Dick Bowdler:

I will briefly describe the principles underlying the assessment of turbine noise in Ireland, the United Kingdom and most of the rest of the world. Essentially, one starts by measuring the background noise and then one assigns a level above that which the turbine shall not exceed. What has also happened here and in the United Kingdom is that in very quiet areas a lower level has been set. In that way, one ends up with a noise limit which is five decibels above the level of background noise, for example, but it varies with wind speed. As wind speed increases, the noise levels of the turbines can be higher. At the very low noise levels, one finds that the guidance puts a lower limit on the turbines. There may be a lower limit of 35 to 45 decibels, irrespective of background noise levels. One of the implications of this is that in quiet rural areas the position is very different from that in residential or mixed residential-industrial areas and urban areas generally. In urban areas background noise levels tend to be higher and people living in such areas are more used to the noise of traffic and so forth. Noises such as those generated by traffic have a similar character or noise spectrum to turbine noise, whereas in rural areas ideally a different method of assessment is needed. People living in rural areas are not used to high levels of background noise and live in a much quieter environment. They are not used to intruding noise from traffic, industrial production and so forth.

On the question of set-backs, in the current Irish guidance there are lower limits, irrespective of background noise levels. The limit is 35 to 40 decibels in areas that are relatively quiet, 43 at night and 45 in a rather undefined way. It is not clear from the guidance when the figure of 45 decibels is to be used. In addition, there is a set-back of 500 m. The problem with set-back is that when the guidance was written, the level of turbine noise at source might have been, for example, 103 decibels, but the sort of turbines about which we are now talking can emit noise at between 107 and 110 decibels at source. Therefore, we are talking about much noisier turbines and because of this, the original set-back distance is probably wrong. I am not keen on having a set-back distance for that very reason and believe setting a noise limit would be a better approach.