Noise Generating Developments & BS4142

Noise generating developments are defined as any development that generates noise. When submitting a planning application for a noise generating development the local planning authority planning departments may request a noise impact assessment. Specifically, they may request a BS4142 assessment. 

BS4142 is a British Standard that provides guidance and a standardised methodology for assessing industrial and commercial noise sources. Industrial and commercial noise sources can include large scale industrial plant and or sites such as waste to energy, recycling centres to smaller commercial development and plant which as car washes, restaurant extraction systems or air conditioning units.

BS4142 Overview

In short, a BS4142 assessment is undertaken by comparing the noise emissions from a specific noise source to the underlying background sound level in the area. These calculations are typically undertaken considering the closest un-associated residential dwelling often called the Nearest Sensitive Receptor or NSR. When comparing the specific noise levels from the noise source in question the higher the noise source emissions above the background sound level the higher the potential for noise impact on the NSR.

Nearest Sensitive Receptor 

The Nearest Sensitive Receptor or NSR is typically defined as the house or residential dwelling closest to the noise source under investigation. However, it should be noted that there are also other types of Sensitive Receptors such as nature reserves, sites of specific scientific significance, schools, places of worship and areas of natural beauty. 

Specific & Rating  Noise Levels 

While undertaking a BS4142 assessment the specific noise emission of the noise source under investigation will be predicted at the closest NSR. If the source under investigation is already operational then these sources may be measured at the Nearest Sensitive Receptor. 

People typically find certain acoustic features of any given noise more perceptible or ‘annoying’. To account for this once the specific noise levels have been measured or predicted at the NSR acoustic feature penalties are then applied to establish a Rating Noise Level. Rating penalties can be applied for features such as Tonality, Impulsivity, and intermittency. An overview of the penalties that can be applied are as follows and work on a scale of how audible the acoustic feature of the noise may be. 

• Tonality 0 - 6 dB

• Impulsivity 0 - 9 dB

• Intermittency 0 - 3 dB

Background Sound Levels 

The background sound level is defined as the underlying sound level of a given area without the noise source under investigation. It is given the acoustic parameter LA90 which denotes the sound level exceeded for 90% of the time. 

Typically the background sound level of any given development site will be established by undertaking a long term noise survey for a minimum of 24 - 48 hours. The typical background sound level is then obtained by statistically assessing the time periods where the proposed industrial or commercial noise source will operate.

BS4142 Assessment

Once the rating noise level at the NSR has been established this is then compared with the background sound level to assess the potential for noise impact. The higher the specific or rating noise is above the background sound level the higher the potential for noise impact may be. If the rating noise level falls below the background sound level this indicates ‘Low Impact’. The impact ratings defined in BS4142 are outlined on a sliding scale and are as follows:

• 10 dB above the Background Sound level or more indicates ‘Significant Adverse Impact’

• 5 - 10dB above the Background Sound Level indicates ‘Adverse Impact Dependent on Context’

• Noise levels below the background sound level indicate ‘Low Impact Dependent on Context’ 

Assessment Outcomes

Should the BS4142 assessment indicate ‘Low Impact’ typically this would be seen as acceptable to the local planning authorities. However local councils planning noise criteria vary across the country this should be clarified with your local planners prior to having an assessment undertaken.

Should the outcome of the assessment indicate ‘Significant Adverse Impact’ or ‘Adverse Impact’ further acoustic design and mitigation measures may have to be implemented to ensure the noise emissions fall below the background sound levels and meet the local planning authorities’ noise criteria. 

Infinity Acoustics offers a comprehensive set of planning noise assessment services and can provide detailed forms of acoustic design and mitigation enquire now on the button below.