Noise arising from permanent industrial or commercial sources is normally assessed using BS4142: 2014 ‘Methods for rating and assessing industrial and commercial sound’.

 

This document was published on 31 October 2014 and supersedes the 1997 edition.
The assessment methodology set out in BS4142: 2014 is based on a comparison being made between the noise level due to the noise industrial or commercial noise source(s) concerned and the prevailing background sound level in the absence of the specific noise source(s) being considered. If necessary the measured or predicted LAeq for industrial noise source(s) concerned is initially corrected for percentage on-times and for significant tonal and/or impulsive components, yielding a ‘rating level’. Corrections of this kind are to be applied on the basis of the way that the characteristics are or will be perceived at any potentially affected noise-sensitive locations.

 

Chapter 11 of the document, which sets out the assessment methodology, is prefaced with the following text:

The significance of sound of an industrial and/or commercial nature depends upon both the margin by which the rating level of the specific sound source exceeds the background sound level and the context in which the sound occurs. An effective assessment cannot be conducted without an understanding of the reason(s) for the assessment and the context in which the sound occurs/will occur. When making assessments and arriving at decisions, therefore, it is essential to place the sound in context.”The document then recommends the following initial assessment methodology: “Obtain an initial estimate of the impact of the specific sound by subtracting the measured background sound level (see Clause 8) from the rating level (see Clause 9), and consider the following.

NOTE 1 More than one assessment might be appropriate:

a) Typically, the greater this difference, the greater the magnitude of the impact.

b) A difference of around +10 dB or more is likely to be an indication of a significant adverse
impact, depending on the context.

c) A difference of around +5 dB is likely to be an indication of an adverse impact, depending
on the context.

d) The lower the rating level is relative to the measured background sound level, the less likely it is that the specific sound source will have an adverse impact or a significant adverse impact. Where the rating level does not exceed the background sound level, this is an indication of the specific sound source having a low impact, depending on the context.

 

NOTE 2 Adverse impacts include, but are not limited to, annoyance and sleep disturbance. Not all adverse impacts will lead to complaints and not every complaint is proof of an adverse impact. In cases where the initial estimate of the impact should modified due to the context the following procedure is recommended:

1) The absolute level of sound. For a given difference between the rating level and the background sound level, the magnitude of the overall impact might be greater for an acoustic environment where the residual sound level is high than for an acoustic environment where the residual sound level is low. Where background sound levels and rating levels are low, absolute levels might be as, or more, relevant than the margin by which the rating level exceeds the background. This is especially true at night. Where residual sound levels are very high, the residual sound might itself result in adverse impacts or significant adverse impacts, and the margin by which the rating level exceeds the background might simply be an indication of the extent to which the specific sound source is likely to make those impacts worse.

2) The character and level of the residual sound compared to the character and level of the specific sound. Consider whether it would be beneficial to compare the frequency spectrum and temporal variation of the specific sound with that of the ambient or residual sound, to assess the degree to which the specific sound source is likely to be distinguishable and will represent an incongruous sound by comparison to the acoustic environment that would occur in the absence of the specific sound. Any sound parameters, sampling periods and averaging time periods used to undertake character comparisons should reflect the way in which sound of an industrial and/or commercial nature is likely to be perceived and how people react to it.

 

NOTE 3 Consideration ought to be given to evidence on human response to sound and, in particular, industrial and/or commercial sound where it is available. A number of studies are listed in the “Effects on humans of industrial and commercial sound” portion of the Further reading list in the Bibliography.

 

3) The sensitivity of the receptor and whether dwellings or other premises used for residential purposes will already incorporate design measures that secure good internal and/or outdoor acoustic conditions, such as:

 

i) facade insulation treatment;

 

ii) ventilation and/or cooling that will reduce the need to have windows open so as to provide
rapid or purge ventilation; and

 

iii) acoustic screening.”