This article outlines and considers the current reasons and methods for industrial noise assessments with respect to neighbouring receptors and offers some practical advice to commercial operators. It does not consider noise exposure assessment as it relates to employees and others for whom operators may have responsibilities under health and safety at work legislation.

Reasons for industrial noise assessments

The key reasons for which an environmental noise assessment might be required are:

  1. To support a planning application for new/altered equipment or activities.
  2. To demonstrate compliance with, or discharge, a Planning Condition.
  3. In connection with the Environmental Permitting Regulations (EPR) (Part A processes only).
  4. In response to a noise complaint (from a resident or via the Council or Environment Agency).
  5. To support a legal challenge (against an adjacent noise sensitive proposal or an Abatement Notice for example).

In all of these cases, British Standard BS 4142:2014 Methods for rating and assessing industrial and commercial sound is likely to form a central plank of the assessment methodology, although other standards, guidance and factors may also carry weight.

BS 4142:2014

The Standard is described as suitable for rating sources of industrial/ commercial sound for the purposes of:

  • Investigating complaints
  • Assessing sound from proposed, new, modified or additional source(s)
  • Assessing sound at proposed new dwellings or premises used for residential purposes The basic approach of BS 4142:2014 is to:
  • Establish the specific sound level of the source(s) at the receptor(s)
  • Quantify the representative background and residual sound levels (these are the prevailing sound levels in the absence of the sound source) at the receptor(s)
  • Correct the specific sound level for on-time (proportion of the reference time interval for which the source operates) and the residual level
  • Rate the specific sound level to account for distinguishing characteristics, e.g. tonality, impulsivity, intermittence etc as perceived at the receptor(s)
  • Estimate the impact by subtracting the background sound level from the rating level
  • Consider the initial impact estimation in the context of the sound and its environs

So the absolute level of the sound (i.e. its decibel level) is not the critical determinant of the initial impact estimation (although this is relevant in the contextual assessment). Initially, the impact is estimated using the difference between rating level and the background level as follows:

  • Typically, the greater the difference, the greater the magnitude of impact.
  • A difference of around +10 dB or more is likely to be an indication of a significant adverse impact (see SOAEL in the table on page 48), depending on the context.
  • A difference of around +5 dB or more is likely to be an indication of an adverse impact, (see LOAEL in the table on page 48) 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. 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.

In the case of examples 2 and 3, this initial assessment might be all that is required, as the structure and wording of the noise condition may obviate the need for wider considerations or even provide a target rating level to be achieved based on a pre-determined or assumed background noise level.

Where planning or permit conditions pre-date 2014, they are likely to specify the now superseded BS 4142:1997 which, whilst similar, is not interchangeable with the extant version. Under these circumstances, assessments should be made using the earlier version as to do otherwise would be contrary to the intent of the condition. Where the Standard is referenced without a date; some assessors may attempt to apply the later version but this is entirely inappropriate when the condition pre-dates its publication.

The context of the sound

In the case of examples 1, 4 and 5 above the numerical aspects of a BS 4142:2014 assessment can only ever comprise a part of an assessment, for a number of reasons. For example, the core methodology takes no account of how frequently assessed sound sources operate. As a consequence, a superficial assessment could portray a very infrequently occurring sound as having the same level of impact as one which occurs continually or continuously.

The Standard requires all relevant contextual factors to be taken into account, before considering if the initial impact estimation should be modified. The factors identified in the Standard are:

  • The absolute level of the sound (usually with reference to the World Health Organisation)
  • The character and level of the residual sound compared to that of the specific sound
  • The sensitivity of the receptor

The importance and significance of the contextual assessment can sometimes be missed, particularly by overzealous enforcement policies or officials, as it did not feature in the 1997 version of the Standard with which some are more familiar. Also, even where the contextual assessment is undertaken, the above factors can be taken as an inclusive list despite the standard stating that ‘all pertinent factors’ should be taken into account.

In truth, the contextual considerations are of paramount importance, particularly in the case of Planning Decisions (application or enforcement decisions) or noise nuisance assessments. In these cases we can find guidance on contextual considerations elsewhere.

Many Councils have local planning policies regarding noise impacts or acceptable industrial/commercial noise levels. Where these policies are outdated or conflict with the National Planning Policy Framework (NPPF) 2012, however, the national policies take precedence (although this often needs to be pointed out). This can be helpful to industrial operators as these national policies tend to be more business friendly, more permissive and less rigid.

Whilst the NPPF is a rather skeletal document, we can find more detail in the Noise Policy Statement for England (NPSE) 2010 and the online Planning Practice Guidance (PPG). These adopt a subjective approach to noise based on ‘observed effect levels’ as summarised in the following table which is reproduced from the PPG:

“the subjective nature of noise means that there is not a simple relationship between noise level and the impact on those affected”

No decibel numbers are correlated with these descriptions as ‘the subjective nature of noise means that there is not a simple relationship between noise level and the impact on those affected’. Instead we are directed to consider how various factors combine, such as:

  • The source and absolute level of the noise together with the time of day it occurs
  • For non-continuous sources of noise, the number, frequency and pattern of noise events
  • The spectral content and general characteristics of the noise
  • The cumulative impacts of more than one source
  • Whether adverse internal effects can be completely removed by closing windows
  • Noise levels in external amenity spaces
  • The potential effect of new residential development on existing businesses

Noise complaints

Whilst in certain circumstances noise complaints may be investigated via planning or permit conditions, they are far more likely to be addressed via the Statutory Nuisance regime. This is because enforcement of the former are discretionary but Councils are obliged to take ‘reasonable steps’ to investigate allegations of statutory nuisance and to serve an Abatement Notice when satisfied that a nuisance exists.

Whereas the Statutory Nuisance provisions are set out in the Environmental Protection Act 1990, Part 3, as amended, there is no statutory definition of what actually constitutes a nuisance so we have to look to a multitude of common law precedents which have arisen over the last one hundred and fifty years or so. Broadly speaking, nuisance is about ‘balancing the rights’ between the noise maker and receiver, seeking to avoid ‘unreasonable interference’ on the latter. In weighing up whether or not something amounts to a nuisance all of the following should be considered and given appropriate weight depending on the facts of the case:

  • The character of the neighbourhood (i.e. in an industrial/commercial area one might expect some noise)
  • The time of day (i.e. sensitivity may be greater at night, in the evenings or at weekends)
  • Duration
  • Intensity
  • Frequency of occurrence
  • Give and take
  • Importance and value to the community (is the noise coming from a large employer for example?)
  • Convention
  • Reasonable behaviour (by the noise maker) and expectation (from the complainant)

As part of a nuisance assessment of industrial/commercial noise, therefore, the actual noise measurement and objective assessment is only one part of the puzzle. It is unquestionably an important part, and would generally follow the principles of BS 4142:2014, but the results cannot be used in isolation as an indication of nuisance (or otherwise). The importance of this can be, and is, missed by some enforcing authorities leading to a blinkered approach to industrial noise assessment.

The concept of ‘Best Practicable Means’ (BPM) is particularly important for industrial/commercial operators as its application is both an appeal ground and a defence against statutory nuisance proceedings. It is a similar concept to that of ‘Best Available Techniques’ (BAT) found in the EPR regime. It can include both physical and management measures appropriate to the industry and the financial burden on the operator is a legitimate consideration. Technically, presenting a strong case that the BPM is employed in minimising the nuisance does not remove a Council’s obligation to serve an Abatement Notice but, in practice, it may persuade a Council that service is inappropriate. After all, they will not want to serve a Notice only to have it quashed on Appeal, wasting time and money for both parties.

An investigating officer may be under considerable pressure from one or more complainants to take action to resolve an alleged noise nuisance. In these circumstances, it may help that officer to manage complainant expectations if the noise maker can provide them with some evidence of BPM and put the noise into context with reference to some of the factors listed above. This type of positive collaboration can also help the investigator to understand, and sympathise, with your business needs.

Practical noise measurement and prediction

So, having said how noise levels cannot be treated in isolation, and how many other important factors must be considered, let us now turn to the technical bit – the actual measurement and prediction of industrial and commercial noise sources.

Firstly; not just anyone armed with a sound level meter can do it and expect to have their results accepted. BS 4142:2014 was produced for the use of ‘appropriately qualified and experienced people’ and a statement of the ‘qualifications, competency and professional memberships’ of all contributing personnel is a reporting requirement.

“some rather data hungry logging should ideally take place to enable objective and reference methods to be applied in the event that subjective character penalties are disputed”

Class 1 instrumentation should be used (this is unlikely to include your smart phone) and should be suitably calibrated and deployed. Some rather data hungry logging should ideally take place to enable objective and reference methods to be applied in the event that subjective character penalties are disputed. Careful professional judgement is required in choosing appropriate monitoring locations at receptors or proxy assessment locations.

It is important for the assessor to quantify the sound source(s) free from interference from unrelated sources and this can involve engineered operational scenarios and/or combinations of measurement and prediction to derive rating levels at receptors. It is equally important for adopted background and residual noise levels to be representative and demonstrably robust. The means by which these are derived is a common source of challenge and disagreement and can be critical in an assessment.

Where new noise sources are proposed; predictions via calculation or 3-dimensional noise modelling may be required using appropriate source data and numerous justified assumptions. If the manufacturer’s acoustic information is inadequate, as is sometimes the case, the assessor may need to source data elsewhere or make measurements of identical plant at a similar installation (if such is available) which may prolong an assessment.

Where replacement plant is proposed, the contributions to the existing baseline noise environment are particularly important. For example, the noise from the old plant which is to be replaced should ideally be measured (and arguably included in the derivation of the residual level) so that any improvement can be quantified. To do otherwise would risk penalising plant which is actually quieter than that which it is replacing. Noise assessments should therefore ideally be initiated before old plant is decommissioned.

It is particularly important for the assessor to understand operating practices and patterns; particularly; where, at what times, how often, and for how long the relevant noise sources operate. The reference time intervals (assessment measurement periods) are set as one hour during the day and fifteen minutes during the night. It will be important for the periods used to be representative of typical operating conditions or presented as a range of scenarios (e.g. worst case and typical case). Where noise sources only operate for parts of these assessment periods, the assessor may need to apply justified on-time or character corrections, so providing them with appropriate and accurate operational information is essential.

On complex sites, where there are numerous significant noise sources, the assessor may need to request some contrived operational scenarios (e.g. different combinations of plant or activities on/off) to permit accurate measurement of the respective sources. If practically possible, this should be facilitated as it should permit a more robust assessment.

Some practical advice for the commercial operator:

  • Maintain positive communications and relations with noise sensitive neighbours
  • If complaints are received; request as many details as possible
  • Consider keeping a site log, focusing on activities which may cause complaint
  • Record details of any investigation or mitigation works you undertake or obtain quotes for
  • Some planning/ enforcement policies are flawed and many conditions are unenforceable
  • Investigating/enforcement officers may have an incomplete understanding of technical and legal requirements
  • Investigating authorities, under pressure from complainants, may prioritise complaint resolution over the needs of businesses (failing to ‘balance the rights’ of both parties)
  • Seek professional advice early –a phone call or email may be all that’s needed
  • Do not be afraid to challenge the authorities (ideally after taking advice)
  • If an assessment is required, employ a suitably experienced and reputable professional
  • The more you engage with your assessor, the more robust the noise assessment is likely to be
  • For new/replacement plant or planning applications, seek professional advice early
  • Noise surveys often require certain operational and weather conditions and these may effect survey timings