Noise Impact Assessments (BS4142) Explained
Noise Impact Assessment (BS4142) 101
A noise impact assessment will usually be requested by the Local Authority / Council when there is a proposed development which will introduce a new source of noise to the local environment. In general, this type of assessment is governed by BS4142 however as we will see below, there are exceptions.
The noise source can take many forms, such as industrial premises, noise from music events, pubs, clubs, cafes and restaurants and external plant items – such as air conditioners and heat pumps. Effectively anything that generates a noise at a residential receptor can be considered. It will be a decision for the Environmental Health Officer usually as to whether a Noise Impact Assessment needs to be provided as part of the planning application.
How Is A Noise Impact Assessment Conducted?
Generally, the first stage is to understand the ambient noise levels in the area, i.e the existing background sound level. This is often done with a noise survey which measures the noise level over a long period of time. This noise measurement data can then be analysed to define the background sound level at the development site.
The next stage is to calculate the specific sound level of the proposed noise source, i.e. how much noise does the source make when heard at nearby residential premises. There are many ways in which this can be done, including acoustic calculations or the generation of a computer noise model. Both of these methods should consider the sound power level of the source, and the propagation to the receptor (including screening effects of barriers, topography and air absorption for example).
Following the method outlined within BS4142, corrections are applied to the specific sound level to account for tonal sound and impulsive sounds – once corrected, the noise level at the receptor is referred to as the Rating Level.
What Are BS4142 Requirements?
Once the background sound level is known and the Rating level is defined – it is possible to conduct a noise impact assessment to BS4142. This method involves a comparison between the background sound level and the rating level. The following guidance is provided within BS4142:
Typically, the greater this difference, the greater the magnitude of the impact. A difference of around +10 dB or more is likely to be an indication of a significant adverse impact, depending on the context. A difference of around +5 dB is likely to be an indication of an adverse impact, depending on the context. The lower the rating level is relative to the measured background sound level, the less likely it is that the specific sound source will have an adverse impact or a significant adverse impact. Where the rating level does not exceed the background sound level, this is an indication of the specific sound source having a low impact, depending on the context.
If the predicted noise impact from the development is too high, mitigation measures will need to be developed – or the application may be simply rejected.
How Can Noise Control Solutions Help?
NCSL Acoustic Consultants are corporate members of the Institute of Acoustics, you can find more details on the IOA website here.
NCSL are able to help at all stages of a noise impact assessment, from initial acoustic planning to noise assessment and finally to mitigation measures where required. If you require any further information, check out our Noise Impact Assessment page or feel free to contact us.