BS 4142 noise assessment
The latest in our “jargon buster” series looks at what a BS 4142 noise assessment is – what it’s intended to cover, how it works, and when you might need to commission one from an acoustic consultant.
BS4142:2014 Methods for rating industrial and commercial sound essentially does what it says on the tin. It’s used for a variety of situations, for example:
- Assessing noise from a new fan or piece of equipment to be installed
- Assessing the potential impact of a new commercial or industrial enterprise on surroundings
- Assessing the likelihood of complaint from residents arising from a new industrial or commercial development
- Quantifying whether existing complaints based on subjectivity have an objective basis for action
It is important to understand that the standard does not allow a nuisance to be determined. It is also not appropriate for use in certain circumstances, for example, to quantify the impact of noise from events and entertainment.
BS 4142 noise survey
The first step in carrying out a BS 4142 assessment is to gather information. This will usually involve a noise survey, which has two aims – firstly, to ascertain the prevailing background noise level (LA90) at the noise sensitive receptors, and secondly, if the noise source to be assessed already exists, to quantify that noise source.
For a prospective development or installation, it is possible to predict future noise levels based on manufacturers’ information. Alternatively, you can take measurements of similar activities. We recently worked for a factory in Huddersfield which was seeking planning permission for an extension. We were able to measure noise levels from their existing equipment, calculate the level of sound breaking out through the proposed structure of the extension, and predict how much noise would arrive at the nearby housing.
The level of noise arising due to the proposed industrial / commercial activity is the ‘specific noise level’, LAeq. This can be adjusted for the ‘on time’ of specific activities during the day and night time period.
Developing the rating level
The ‘rating level’ is developed from the specific noise level, but if appropriate includes corrections for specific noise characteristics. For example, if the proposed noise source will be intermittent, tonal (whiny), contain bangs or clanks, or any other characteristic which would make it particularly noticeable, a correction is added to the specific noise level. The latest iteration of BS 4142 allows for a variety of corrections to be added at the discretion of the surveyor/assessor – this is in contrast to the flat +5dB correction provided for in the previous iteration of the standard.
Assessing the likelihood of noise complaints
Assessments are based on 1 hour during the day, and a 15 minute period at night (11pm-7am). The rating level is compared to the background noise level, and the difference is used to give an idea of the likelihood of complaint: the greater the difference, the greater the likelihood of complaint.
A difference of around +10dB 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.
You can see that this remains quite a woolly and subjective assessment – although the wording has been changed in this iteration of the standard, there is still a lot of flexibility according to ‘context’, and little guidance. This is where using a professional consultant can be vital; they will negotiate with the planning officer on your behalf to agree an appropriate level for noise emissions.
Do I need a BS 4142 assessment?
It’s likely that if you are seeking planning permission for an industrial use, or for new externally mounted plant, a planning condition will be set requiring that an assessment is carried out and submitted before work commences.
You may also want to consider an assessment if you are considering equipment or activity for which you don’t need planning permission, but which may have an effect on your neighbours. It can be wise to protect yourself by establishing baseline noise levels before you go ahead, so that there is a reasonable rebuttal should any complaints be received in future.
How do I commission an assessment?
Make sure you are talking to a competent consultant who is a full member of the Institute of Acoustics (MIOA). They will be able to talk through your specific project and provide you with a clear scope of work and fee to get the job done.
dBx Acoustics has extensive experience of BS 4142 noise assessments, and of helping to design noise control solutions to ensure that planning is achieved. If you would like to know more about how we can help you, please contact us.