BS4142 (1997) Noise Impact Assessments
Method for Rating Industrial Noise Affecting Mixed Residential and Industrial Areas
This standard is a method for assessing the impact of new industrial and commercial noise sources in mixed residential and industrial areas. It is also often used by local authorities in determining planning applications or for assessing noise nuisance or disturbance from noise sources such as mechanical services and machinery.
The assessment method is to compare the Rating Level of the industrial noise, as experienced at the residential properties, with the existing Background noise level in the area.
If the noise is described by any of the following: " contains a distinguishable, discrete continuous note (whine, hiss, screech, hum etc); contains distinct impulses (bangs, clicks, clatters, or thumps); is irregular enough to attract attention " , then a correction is applied. The correction is +5dB if one or more of the above are present. This is added to the Specific Noise Level and the resulting value is called the Rating Level.
There is a daytime assessment method and a night time assessment method to use depending when the industrial noise is made however both methods compare industrial noise to background noise.
A difference of around +10dB is an indication that complaints are likely. A difference of -10dB is a positive indication that complaints are unlikely. A difference of around +5dB is of marginal significance in a BS4142 assessment.
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