BS4142 1997 Method for Rating Industrial Noise Affecting Mixed Residential and Industrial Areas:

The standard is used to support planning applications for the introduction of industrial type noise sources in to mixed residential areas. The assessment compares the noise source with existing background noise.

The noise source is either measured or acoustic data taken from the manufacturer’s information for the item or plant of interest. A background noise survey must be performed during the proposed operating hours. The worst hour during day time is taken, and the worst 10 minutes at night.

Following analysis and corrections to the data in accordance with BS4142 the difference between the source and existing noise level is determined.

A difference of +10dB is a positive indication that complaints are likely. A difference of -10dB is a positive indication that complaints are unlikely. A difference of +5dB is said to be of marginal significance.