PPG24 and ProPG do not really deal with industrial noise and instead refer the reader to BS 4142, which provides a means of rating industrial noise affecting mixed residential and industrial areas.
The 1997 version of B.S.4142 rates industrial noise by comparing the predicted or measured Leq noise level from the industrial activity with existing background L90 noise levels. If the industrial noise, after correcting for special characteristics, exceeds the background noise by 10 dBA or higher, complaints are likely. A difference of 5 dBA is of marginal significance and smaller differences give lesser likelihood of complaints, until a difference of -10 dBA means that complaints are unlikely.
In order to conduct such an assessment it is necessary to measure the L90 background noise levels with the industrial noise absent, and the industrial noise needs to be of sufficiently long duration to enable a representative Leq to be measured.
For a daytime B.S.4142 assessment the industrial noise needs to be measured or calculated over a reference time interval TR of 1 hour. For a night time B.S.4142 assessment the reference time interval TR is 5 minutes.
A later version of BS4142 was introduced in 2014, which is considerably more involved and more complicated than the 1997 version. The main differences, apart from the need to conduct more extensive measurement and analysis, relate to the rating level of the acoustic features of the noise source with different methods for assessing the rating penalty and different corrections for noise source characteristics of tonality, impulsivity, distinctiveness and intermittency. The assessment period has now changed to 15 minutes for night time, but the daytime assessment period has remained unchanged at 1 hour. Also the rating criteria terminology has changed to ‘significant adverse impact’ for a noise level difference from L90 background of +10 dB, ‘adverse impact’ for +5 dB difference, down to a ‘low impact’ where the rating level does not exceed the background level.
Examples of industrial noise assessments undertaken include roof mounted plant at Chard, car wash schemes, scrap yard operations, supermarket deliveries, dog kennel expansions and metalwork fabrication.