BS 4142 Industrial Noise Assessments
BS 4142:2014 (+A1:2019) industrial noise assessments – methods for rating and assessing industrial and commercial sound
Industrial and Commercial Sound
- for investigating noise complaints;
- for assessing sound from existing, proposed, new, or modified sources;
- and for assessing industrial/commercial sound at new or proposed residential premises.
The standard was born out of Appendix XV of the Wilson Committee report as an indicator of impact on amenity and the most recent version of the standard directs that it is now intended only to be used, by ‘appropriately qualified and experienced people’.
The current version of the standard no longer considers the ‘likelihood of complaint’ but the ‘magnitude of the impact’ taking into account the context in which a sound occurs and is based on a comparison of the sound under investigation with the ‘background sound level’ or level exceeded for 90% of the time (often referred to as the LA90) and is the quietest 10% of any measurement period.
In a BS 4142 assessment the sound from the source will be referred to as the ‘specific sound’ and can be obtained by subtracting the ‘residual sound’ which is the existing sound at site in the absence of the specific sound, from the ‘ambient sound’ which includes sound from all sources both near and far as well as the specific sound.
BS 4142 recognises that sound with certain characteristics may be rated as more intrusive than a simple numerical comparison might otherwise suggest and outlines a series of methods to identify corrections that can be applied to the specific sound.
Corrections may be applied for tonality, impulsivity and intermittency.
Where none of these apply, a correction for ‘other sound characteristics’ may be used if the specific sound readily distinctive against the residual sound. Once any corrections are applied to the specific sound, it becomes the ‘Rating Level’.
As part of a 4142 assessment the Rating Level is compared with the Background Sound Level and the difference provides the initial indication of the magnitude of the impact. The lower the rating level relative to the measured background sound level, the less likely it is to have an adverse or significant adverse impact.
BS 4142 advises a difference of around +10 dB or more is likely to indicate a ‘significant adverse impact’ while a difference of around +5 dB is likely to indicate an ‘adverse impact’ depending on the context.
The use of ‘Context’ in BS 4142 is to provide a greater frame of reference for the assessment.
Context refers to a series of pertinent factors to be taken into account which include:
- The absolute level of sound;
- The character & level of the residual sound compared with the specific sound and how much it may be incongruous by comparison with the residual acoustic environment;
- The sensitivity of the receptor and whether these incorporate measures to secure good internal and external acoustic conditions, such as facade insulation treatment, ventilation and/or cooling options to reduce the need to open windows for rapid ventilation and any acoustic screening.
In addition to context, BS 4142 places a great deal of importance on considering ‘Uncertainty’ as part of any assessment.
Addressing uncertainty includes identifying and explaining steps taken to reduce uncertainty in the measurement values and considering how certain factors might influence calculations and the assessment outcome.