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BS4142 Assessments

 BS4142 is widely used by acousticians and environmental health departments to assess various types of industrial/commercial sound and the subsequent impact e.g. noise from a factory, an extract fan, a delivery van etc. Typical uses of the standard include assessing whether a new industrial/commercial process could cause an impact on nearby existing noise sensitive locations (e.g. houses) or assessing the suitability of a site for residential/noise-sensitive use, considering existing sources of industrial/commercial sound in the locality. 

 

Originally published in 1963, BS4142 is reportedly not only the biggest selling acoustics related standard but the biggest selling British Standard. The reason for its wide use and enduring popularity can largely be attributed to both its importance in the planning process and its use as a tool to establish the likelihood of future complaints.

 

The revised standard (published in October 2014) has undergone significant revisions since its last issue in 1997. For those involved with the assessment of noise impact, the change is monumental.   

Headline changes in the revised standard include:

1. Only experienced professionals in acoustics should use the standard;

 

2. Despite being deemed suitable for investigating complaints the standard makes it clear that it should not be used for determining nuisance. This includes private, public and statutory nuisance. The assessment of industrial/commercial sound (as noise is simply unwanted sound to a human receptor) no longer considers the likelihood of complaints. Consideration is now given to whether the sounds are likely to have either an ‘adverse impact’ or a ‘significant adverse impact’;

 

3. The assessment range has been reduced from 20 dB to 10 dB;

 

4. The correction for the acoustic character of a sound has been changed from a flat +5 dB to a graduated approach covering the tonality of the sound, the sound’s impulsivity and whether or not the sound is intermittent. The effects are cumulative which allows a sound to potentially attract a correction of up to +18 dB. The character correction was previously subjective only (i.e. based on nothing more than judgment). The character correction can now be either subjective, as previous, or based on established objective methodologies;

 

5. The ‘reference time period‘ for night-time noise measurements has been increased from five minutes to 15 minutes;

 

6. Weather data now needs to be considered for each measurement location;

 

7. Uncertainty now needs to be considered and reported;

 

8. Any numerical assessment must be considered in the appropriate context which can greatly modify the conclusions.

This last clarification (as the use of context was buried in previous editions) is of the greatest importance. The application of the context in the assessment greatly increases the level of ambiguity that applies to a BS4142 compliant noise impact assessment as opposed to the previous version which was much more 'binary' in application and conclusion.

 

As a result of the changes, costs associated with a BS4142 assessment will increase with no clear and defined conclusions. However, the context (which is heavily reliant on the opinion of the professional acoustician undertaking the assessment) can now mean that development that would have been restricted before may now be considered acceptable. For example, if the previous standard was used to assess the suitability of a new residential scheme next to a factory, the conclusions would most probably be negative. However, under this edition, assuming the dwellings have been properly acoustically designed, this development may now be possible.

 

The introduction of the NPPF (2010), the Supreme Court’s Coventry vs Lawrence judgment (26 February 2014) and the publication of the Planning Practice Guidance (6 March 2014) have introduced powerful tools to assist with the assessment of the effects of noise sensitive developments near industrial/commercial premises. The latest edition of BS4142: 2014 provides another powerful weapon in the fight against planning refusals on the grounds of noise nuisance near industrial/commercial sources for otherwise perfectly acceptable developments.