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What is BS 4142?
British Standard 4142 (or BS 4142) is a commonly used standard for rating and assessing industrial or commercial sound.
A BS 4142 assessment is usually required when a development introduces a new noise source into a sensitive location, or when a new residential development is to be situated near an existing commercial or industrial noise source (e.g. a factory, restaurant or car workshop)
When is a BS 4142 assessment required?
BS 4142 is used by acoustic consultants and Environmental Health Officers (EHOs) either during the planning and design stage of a development or to assess noise from an existing source.
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BS 4142 noise assessments are most commonly required in the following scenarios:
when a planning application is being submitted for a development which introduces a new industrial or commercial noise source into an area where there are noise-sensitive residential receptors.
when a planning application is being submitted for new residential dwellings that are to be located near to an existing source of industrial or commercial noise.
when a noise complaint is being investigated which has been attributed to a noise of an industrial or commercial nature.
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Although BS 4142 refers to 'industrial' and 'commercial' sound, it can also be applied to small fixed plant installations such as residential air conditioning units.
What's not covered by BS 4142?
Some sources of noise should not be assessed using BS 4142. So-called 'anonymous' noise sources including traffic on public roads, rail or air traffic sources should not be assessed using BS 4142 because there are are other standards written for these purposes. Similarly, construction noise and sound from wind farms are assessed using different standards.
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Noise from animals in domestic settings, amplified music and speech are not covered by BS 4142 because of certain characteristic of these sound sources.
animals in domestic settings or music. This is because there are other British Standards which cover these sources of noise, or because the methods described in BS 4142 would not be appropriate for ass
What's involved?
The basic method of BS 4142 is to compare the 'rating level' of the sound being assessed against the 'background sound' level. Here's some of the basic elements of a BS 4142 assessment - and some of the jargon explained!
Background Sound Survey
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The background sound level, which is the typical sound level in the absence of the source being assessed, will usually need to be measured by way of a sound survey at the site in question. Weather-proof equipment will be set up to log noise levels over a period of (normally) a few days. In rare cases where its not safe or practical to leave equipment unattended, surveys can be carried out over shorter periods.
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Care must be taken to ensure that the sound source being assessed does not influence the background sound measurements. It's also important to remember that the survey needs to represent the background sound at the noise-sensitive receptors, rather than at the location of the sound source being assessed.
Establishing the Specific Level of the Source
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The sound level of the source being assessed can be established using a number of different methods. If the source is already operating (for example in a noise-complaint situation) then actual sound measurements should be taken of the source 'in-situ'. Sound measurements can be made either at the location of the receptor, or in proximity to the source with corrections applied to determine the level at the receptor. Either way, the sound level is always assessed at the receptor location(s).
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If the source under assessment hasn't been installed yet, for example if the assessment is being undertaken during the planning and design stages of a development, then predictive methods can be used to establish sound levels. Predictions might involve using manufacturer's acoustic data or using representative sound data from a similar sound source.
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Calculating the Rating Level
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Once the sound level of the source has been calculated at the receptor, the assessor has to decide whether any 'character corrections' are appropriate.
Under BS 4142 there are certain acoustic features which, if present, attract a penalty of a certain number of decibels (dB). The penalty depends on the type of characteristic, e.g. tonality (hums, drones and tones), impulsivity (crashes and bangs) or intermittency and the degree to which those characteristics are expected to be noticeable. The assessor is permitted to make subjective judgements or to use technical objective methods to establish which acoustic features might be present. This is particularly tricky if the sound source isn't operating yet, and can often cause disagreements between parties where subjective methods are relied upon.
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The 'Rating Level' is simply the sound level of the source, at the receptor location, following the application of any feature corrections.
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Making an assessment
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The Rating Level is compared against the Background Sound Level to make an initial assessment of the 'impact' of the sound. According to BS 4142:
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where the rating level is around 10 dB or more than the background sound level, this indicates a significant adverse impact, depending on the context.
a rating level of around 5 dB above background indicates an adverse impact.
where the rating level does not exceed the background level, this is an indication of the source having a low impact.
