The Sounding Board

Noise Impact Assessments & BS 4142 – The Basics

By December 28, 2018 One Comment

In this blog post, we are going to look at noise impact assessments – in particular, what they are, why we need them and how we conduct them.

So, what are they? Essentially, a noise impact assessment is a way of predicting or measuring the effect that a noise source will have upon the local acoustic environment in order to protect local residents and to prevent any annoyance due to noise.

The British Standard BS 4142:2014 (Methods for rating and assessing industrial and commercial sound) sets out the measurement methods which should be followed when conducting noise impact assessments, and, unless otherwise requested by the local authority, this is the method that will be used.

The standard is applicable to proposed, new, modified or additional noise sources and when a planning application is submitted to a local authority including one of the above, a noise impact assessment should be requested.

Within the impact assessment, there are several factors which need to be considered. Firstly, the existing background noise levels at the nearest residential properties (also known as the Noise Sensitive Receptor or NSR) need to be defined, generally in the form of a long term noise survey covering several daytime and night time periods. This is termed the ‘background sound level’.

The next stage involves the calculation or measurement of the noise level generated by the proposed noise source as observed at the NSR. If the equipment is already installed, this is done by taking acoustic measurements at the residential property with and without the noise source active. From these measurements it is possible to calculate the background noise and the noise generated by the source, which is known as the ‘rating level’. Of course, there will also be occasions where the equipment has not yet been installed, in which case, a prediction model can be used to estimate the rating level at the NSR.

BS 4142:2014 provides guidance on the expected level of noise impact based on the difference between the background sound level and rating level. In situations where the rating level is 10dB higher than the background sound level ‘significant adverse impact’ is expected. Where the difference is 5dB, an ‘adverse impact’ is expected. The lower the rating level is relative to the background sound level the less likely that an adverse impact will be observed.

In instances where a significant or adverse impact is expected, corrective measures will be required before the planning application is approved.

At NCSL, we provide services to complete noise impact assessments in full, including remedial work as and when required. If you would like any further information, have any comments or would like to discuss a noise impact assessment with our experts, please contact us.

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