The document published in 1996 is the report of the Working Group on Noise from Wind Turbines and contains details of assessment methodologies and criteria. The Working Group consisted of representatives from the industry, consultants and local authorities. The report is not a government document but is referred to in current government guidance as the appropriate method for assessing wind farm noise.
The document provides a simplified noise criterion of 35 dB LA90 for single turbines, or groups of turbines with a very large separation distance to the nearest properties. Where the simplified approach is not appropriate, a suitable background noise survey is required and noise limits are set using either background noise levels plus 5 dB or fixed limits, whichever is the higher. All limits are set in terms of dB LA90.