A critical analysis and evaluation of the impact of the changes from BS4142:1997’s to BS4142:2014

Posted in Acoustic Consultants News on Feb 11, 2019



The British Standard BS4142 has evolved significantly since its inception in 1967, the basis of its effectiveness is upon accumulated experience and application of previous editions. The most recent publication in 2014 has seen the most comprehensive revision of the standard. There have been a significant number of changes to the 1997 edition in the 2014 edition, which is the topic of this report. One of the key changes within the standard is the requirement for ‘context’ to be applied to the assessment, which has resulted in additional considerations to be adopted in the application of the methodology. These considerations provide an increase in veracity of the assessments which will aid significantly in assessing the level of impact. As a result this has brought increasing emphasis onto the requirement for ‘appropriately qualified persons’ to be applying the standard. The scope of the standard has been refined, allowing appropriate application of the standard. The provision of additional detail within the methodology allows the assessor to apply detailed analysis and justification for the outcomes of an assessment. The inclusion of a new method of applying corrections to the rating level, considering the character of the sound, will lead to a significant variation in the rating level and thus render significantly different results to that of the 1997 edition. The alterations in the majority are justified, however in part they have been contradicted by professional bodies and remain unjustified.

1.0 Introduction

The British Standard BS4142 is widely applied to the analysis of industrial noise by acoustic consultants and environmental health departments. In October 2014 the British Standard BS4142:1997 – Method for Rating industrial noise affecting mixed residential and industrial areas, was superseded by the release of BS4142:2014 – Methods for rating and industrial and commercial sound. The alterations has been derived from the application of the previous standard and accumulated experience. An extensive review was undertaken, involving industry professionals, the result being the refined BS4142:2014.


The implication of societal changes over the last 50 years have led to a requirement for the control of environmental noise from industrial noise sources and the requirement for an analysis method and criteria of suitability that is applicable to improving the amenity of receptors and reducing the potential of adverse health within the community due to noise. The issue of industrial noise and the requirement for mitigation was surmised by Terrence K Wilson;

As standards of living improve, the population of a country becomes aware of inconveniences and damage caused by the side-effects of industrial activity. That is not to say that the problems necessarily become any worse – although increasing mechanisation of industry may cause additional difficulties – but that the population’s perception of these effects changes. At some stage in its industrial development, a country will allocate monetary resources towards the alleviation of the side-effects of the processes by which it gained its wealth. Noise is an insidious by-product of almost all industrial developments”. (Terence, K. W. 1981)


The presentation of this issue has seen the development of an industrial noise standard used to analyse the potential impact of industrial noise on residential and mixed industrial areas. The method of analysis and results are based upon what is deemed to be an acceptable criteria for noise impacting on amenity and upon on health. However, the requirements of a constantly evolving society alter and by default the methods and acceptability will evolve with time. Current research shows that there is sufficient scientific evidence that exposure to noise can lead to adverse health effects, which is defined by the World Health Organisation;

“an adverse effect of noise is defined as a change in the morphology and physiology of an organism that results in impairment of functional capacity, or an impairment of capacity to compensate for additional stress, or increases the susceptibility of an organism to the harmful effects of other environmental influences” (WHO 1999)


Evidence has also been presented by DEFRA on the changes in attitudes towards noise, based on two research studies carried out in 1990 and 2000. These involved a study into the exposure of the population to noise and found that 55% of the population were exposed to daytime noise levels above the WHO Guideline values of 55dB and 68% were exposed to night noise levels above the night noise WHO Guideline values of 45dB. (DEFRA 2008)

The effect that noise has on health and annoyance has been analysed across multiple countries with the aim to categorise human response to different types of noise. The aim of these studies is to present a suitable analysis and noise criteria for assessments. However industrial noise has had significantly less research, as the character of the source is very diverse. In 2002, Dr Miedema produced a Journal for the Acoustical Society of America. He reviews the existence of dose response curves for transportation noise and states the following in relation to industrial noise;

Such relationships have not been established for industrial noise, presumably because this noise is less widespread than transportation noise and because industrial noise is heterogeneous due to the different types of industrial activities that cause noise. Nonetheless, locally industrial noise causes considerable annoyance, and having relationships for these sources that predict the noise annoyance on the basis of the exposure would help in dealing with this noise.” (DEFRA 2004)

This is clarified by the following statement in BS4142:1997;


“The user is reminded that this standard is not based on substantive research but rather on accumulated experience.” (BSI 1997) 


These comment highlights the complexity of industrial noise and thus the baseline for an acceptable criteria in the evaluation of an industrial noise source, due to the lack of substantive research. When considering the potential impact on health and amenity, the increase in the percentage of the population being exposed to noise, in conjunction with the lack of research on the impact of different industrial noise sources upon people and the associated acceptable criteria for impact. This outlines the requirement not only for a detailed analysis method which is applicable to multiple scenarios and that minimises uncertainty in its application but a method that provides accuracy taking consideration for the context of the investigation. This report aims to outline how the changes to BS4142:2014 have altered the outcome of the assessments.

1.1 Aim

Critically evaluate the variation and the subsequent effect on rating level between BS4142:2014 and BS4142:1997.

1.2 Objectives

The purpose of this report is to:

  • Provide a critical review and analysis of the comparisons between the 1997 and 2014 editions of the standard.
  • Evaluate and discuss the significance of the variations and the effect on the outcome of the assessment between the 1997 and 2014 editions. Where applicable undertake assessments to highlight the difference.

1.3 History of BS4142

The inception of BS4142 was in the form of an appendix to the Wilson Report 1963. The Wilson Report was the first major examination into the extent of noise problems and potential mitigation within the UK. The government appointed Sir Alan Wilson as chair of the committee to ‘Examine the nature, sources and effects of the problem of noise and to advise what further measures can be taken to mitigate it’ (HMSO 1963). The Wilson committee, carried out a substantial investigations of various aspects of noise, including transport, industrial, constructional and entertainment. From which the Wilson Report was published, this report was held in high regard and had a lasting impact on the assessment of environmental noise. Appendix XV of the report presented a ‘Simplified procedure for assessing reaction to industrial noise in mixed residential and industrial areas’, the document describes that;

It is a quantitative guide to whether an existing industrial noise is likely to cause complaint from those people, having a normal reaction to noise, who live nearby and also to give an indication of the probable limiting level of noise from a proposed factory without likelihood of complaint” (HMSO 1963).

The Wilson Report provided the baseline for the release of the first BS4142 standard in 1967, BS4142:1967 – Method of Rating Industrial Noise Affecting Mixed Residential and Industrial Areas. The 1967 edition of the standard required measurements made using a meter set to A-weighting and a slow time response, it included corrections for tonal character, impulsive character and a correction for intermittency and duration. There follows a brief description of the measurement of ‘background’ and ‘ambient’ noise levels and how to establish an alternative to this measurement using basic and corrected criteria. Situations are derived from the increase in noise levels as to whether complaints are to be expected and where complaints are not to be expected. The criterion presented was of 50dB(A) with adjustments for type of installation, type of area, time of day and season (BSI 1967). The 1967 version was amended in 1975, 1980 and 1982, then being revised in 1990 to align it with ISO1996: Parts 1 – 3. BS4142:1990 was superseded by BS4142:1997, the 1967 and 1997 standards aligned in the determination of a background noise level based upon the L90, the noise criteria and correction for tonal features. However, the 1967 edition provides an indication of expectation for levels of background noise in different land use types, against which the industrial noise in question can be compared. The 1997 edition presents measured background noise level as the only basis for comparison. This evolution has led us to the release of BS4142:2014 which has had a significant and comprehensive revision.

1.4 Formation of BS4142:2014

The British Standards Institute (BSI) reviews and re-drafts standards every 15 years. In 2012 the 15 year mark had been reached for the 1997 edition of BS4142. At this point the committee (EH/1/3) carried out a review of the documentation and decided a substantial revision was required. This process involved the creation of a drafting panel, which was represented by The Association of Noise Consultants (ANC), The Chartered Institute of Environmental Health (CIEH), The Environmental Agency (EA) and The Institute of Acoustics (IOA). The re-drafting sought the views and guidance of users, to establish a structure and scope for the re-write. The draft standard was then prepared for public consultation on October 2013, during this time 943 comments were collated. The magnitude of the response to the re-drafting required an expansion of the drafting panel, which resulted in the publication of BS4142:2014 in October 2014.

2.0 Methodology

The objective of this study is to critically review and evaluate the amendments to the new edition of BS4142, with the aim of comparing and contrasting the impact of the amendments to the rating of industrial sound. The process will involve two stages:

  • Critically review and analyse the variations between the 1997 and 2014 editions.

The standard will be compared and contrasted section by section to allow the key changes to be identified and analysed.

  • Evaluate and discuss the significance of the variations and the effect on the outcome of the assessment between the 1997 and 2014 editions. Where applicable undertake assessments to highlight the difference.

The second stage of this study will undertake comparative assessments, this may not be appropriate for all variations outlined. It is important to understand the potential impact of each separate alteration, which will subsequently allow the cumulative impact of the changes to be discussed. Therefore real examples and hypothetical examples are provided outlining the potential impact of each variation individually. This section of the study will utilise projects undertaken by the author within the last year, to provide primary data for the assessment. The number of comparisons is restricted due to the significant variation in the type of assessment and method of applying the standard. The following case studies are used within the analysis:

Case Study 1:

This assessment was analysing the change of use of a commercial unit, with the introduction of 4 refrigeration units that would be in operation 24 hours a day at the rear of the property. The commercial units had dwelling flats above and thus concern had arisen over the impact on amenity of the occupants of the flats. Background sound levels were monitored during a 24 hour period at the noise sensitive receptor (NSR), the night time period is highlighted within this example. The background sound level was monitored in 5 minute samples at the NSR’s window.   

Case Study 2: 

This predictive assessment was analysing a proposed warehouse and production line facility, operating during daytime hours. The analysis of operations and potential noise sources showed that the only external noise source was the delivery yard, which would be receiving and sending goods, with 4 – 5 deliveries/collections per hour during the day. The Local Authority requested a BS4142 noise survey in support of the planning application, as the site was located in close proximity to residential dwellings. A background noise survey was undertaken to outline the noise profile of the area without the unit in operation and the specific noise level was calculated at the receiver.

Case Study 3:

This assessment was analysing the impact of a large extraction duct installed at the rear of a new fast food outlet. The ducting was located on the rear of the commercial building and the ducting terminates at the 4 the fourth floor. The route of the ducting passes close by windows for the residential units on the 2nd, 3rd and 4th floor.  Complaints have arisen from the use of the extraction system and the local authority requested a BS4142 assessment to provide appropriate mitigation to reduce the noise emissions to a satisfactory level. 

3.0 Summary of key changes to BS4142:2014

  • Clarification is provided on the classification of sound of an industrial or commercial nature.
  • Clarification of how the standard is applicable to determination of sound levels at outdoor locations. Including the new application of assessing sound at proposed new dwellings or premises used for residential purposes.
  • Clarification of sound of an industrial and/or commercial nature that is not covered within the scope of the standard.
  • Clarification that the standard is not applicable to low frequency noise.
Terms and Definitions
  • The introduction of the term ‘sound’ instead of ‘noise’.
  • This section is new to the 2014 edition and reviews the requirement for the assessor to gain an appropriate understanding of the context of the situation.
  • New requirement to use a Class 1 sound level meter.
Measurement Procedure
  • The field calibration check now has a specific criteria, stating that pre and post calibration that exceed 0.5dB should be treated with caution.
  • Weather conditions are required to be monitored in more detail at each measurement location including, wind speed/direction, rainfall, temperature, oktas. There is the requirement for meteorological stations at long term monitoring positions.
Specific Sound Level
  • The night time reference time interval has been increased to 15 minutes.
Background Sound Level
  • An emphasis on representative background sound levels is required, an approach of a statistical analysis is presented to ascertain the most commonly occurring values.
Rating Level
  • Significant alterations have been made to this section which include the introduction of 3 methods to analyse the acoustic features of the specific sound level. Which are the subjective method, the objective method for tonality and the reference method.
  • A new section has been added with requirement of uncertainty to be assessed for measured values and within calculation.
Assessment of Impacts
  • An emphasis is presented on the requirement for context within the assessment of impact.
  • The noise criteria has changed to the following:
  • 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.
  • The factors affecting context are outlined and summarised below:
  • Take consideration for the use of absolute levels for sensitive or complex scenarios.
  • Take consideration for the character of the residual sound and specific sound, analysing the prominence of the specific sound level and whether it presents an incongruous sound by comparison to the acoustic environment.
  • The sensitivity of the receptor.

Table 3.1 - Summary of Key Changes to BS4142:2014

4.0 Critical Analysis and Evaluation

4.1 Scope

4.1.1 Critical Review and Analysis

The scope of the standard has been increased by the alteration of the title and the listed applications in the initial section 1.1. The 1997 edition was titled specifically in relation to industrial noise, however the 2014 version is sound of an industrial and/or commercial nature with no clarification being provided as to the definition of commercial sound. It is assumed that this is in line with the extension to scope in section 1.1 of associated industrial sound such as, sound from loading and unloading goods and mobile plant. The title has also removed the term ‘affecting mixed residential and commercial areas’, it could be argued that this is increasing the general application of the standard as it is not explicit in the type of receptors, however alongside the extension in scope this is unlikely.

The 2014 version provides more detailed applications (underlined) as follows;

a) noise levels from factories, or industrial premises, or fixed installations, or sources of an industrial nature in commercial premises; and
Section 1.1
a) sound from industrial and manufacturing processes;
b) sound from fixed installations which comprise mechanical and electrical plant and equipment;
c) sound from the loading and unloading of goods and materials at industrial and/or commercial premises; and
d) Sound from mobile plant and vehicles that is an intrinsic part of the overall sound emanating from premises or processes, such as that from forklift trucks, or that from train or ship movements on or around an industrial and/or commercial site.
b) Background noise level. The standard also describes a method for assessing whether the noise referred to in (a) is likely to give rise to complaints from people residing in the building. The method is not suitable for assessing the noise measured inside buildings or when the background and rating noise levels are both very low.
Section 1.2
a) rating levels for sources of sound of an industrial and/or commercial nature; and
b) ambient, background and residual sound levels, for the purposes of:
1) investigating complaints;
2) assessing sound from proposed, new, modified or additional source(s) of sound of an industrial and/or commercial nature; and
3) Assessing sound at proposed new dwellings or premises used for residential purposes.

Table 4.1 – Comparison of changes to scope from 1997 to 2014

Section 1.1 has more detail and provides clarification on the appropriate applications for the standard to specific scenarios, compared with the vague section within the 1997 edition.  Section 1.2 largely remains the same, however there is the addition of applying the standard to assess sound at proposed new dwellings or premises for residential purposes. This has the potential for areas of land that are prime for residential development not being utilised due to the proximity of industrial noise sources. Mitigation can easily be implemented to reduce internal noise levels for residential dwellings, however external amenity will be more challenging to achieve. This may lead to a further increase in the population being over exposed to noise or, in relation to National Planning Policy Framework (NPPF) and the Noise Policy Statement for England (NPSE), this may lead to ineffective use of land through reliance on mitigation through distance separation. The 1997 version does not state this as an appropriate application, even though the standard BS8233: 2014 – Guidance on sound insulation and noise reduction in buildings refers to the application of BS4142 as an appropriate method of analysing industrial noise at new residential premises.

Section 1.3 is a new section to the 2014 edition, which provides clarification as to sources that the standard is not applicable to, including:

  • The passage of vehicles on public roads and railway systems
  • recreational activities, including all forms of motorsport;
  • Music and other entertainment;
  • Shooting grounds;
  • Construction and demolition;
  • domestic animals;
  • People;
  • Public address systems for speech; and
  • Other sources falling within the scopes of other standards or guidance.
  • Indoor sound levels arising from sound levels outside, or the assessment of indoor sound levels.
  • The standard is not applicable to the assessment of low frequency noise.

The IOA consultation response on the extension of scope stated;

 “Additional detail in the standard is welcomed e.g. clarification of its scope and the reinforcement of use of the typical background, because it will help ensure practitioners carry out thorough noise investigations that yield sensible results”. (IOA 2014)

Further to this they go on to say:

“The IOA agrees that clearly defining the scope of the standard is important. Disagreements over the scope and possible misapplication of the standard have been a known problem for many years.” (IOA 2014)

This point clarifies the use of BS4142:1997 in a more general application, this is due to the purposeful vagueness of the standard. As outlined in the foreword;

“The standard is necessarily general in character and may not cover all situations.” (BSI 1997)


As stated by the IOA there is a known misapplication of the standard, however this was due to it being general in nature and easily applicable to other scenarios. Especially in the light of there being no appropriate method or substantive research into methods of analysing or the associated criteria of impact for certain sources, such as domestic animals. The extension to scope should provide appropriate guidance in outlining the misapplication of the 2014 edition.

4.1.2 Evaluation & Discussion of the effect on the assessment

The extension to scope provides increased clarification as to the appropriate application of the standard, the alteration has no quantifiable effect on the rating level. The purpose of the alteration is to avoid misapplication of the standard to inappropriate sources of noise. The misapplication of the standard is likely to continue, as it provides a known and practised method of assessing noise sources. Further to this the criteria of the rating level being below (-10dB) the background sound level, in most cases, provides a good indication for low impact. This is because it is widely accepted that if a source of noise is 10dB below another source it is of low significance, or inaudible dependant on the frequency and characteristics of the sound. If the standard is misapplied the author will be required to provide appropriate justification as to why the method has been used. Refining the focus of the standard is likely to improve the application for its intended purpose which is beneficial in relation to attaining reasonable results from the assessment procedure, thus improving the validity of the assessment.  

4.2 Terms and Definitions

4.2.1 Critical Review and Analysis

The 2014 edition has applied the use of the term ‘sound’ instead of ‘noise’. This amendment is explained in the foreword;

“Sound can be measured by a sound level meter or other measuring system. Noise is related to a human response and is routinely described as unwanted sound or is considered undesirable or disruptive.” (BSI 2014)


The Wilson Report defined noise as “Sound which is undesired by the recipient”. (HMSO 1963)

The introduction of the term sound is a small amendment, but as explained above, it is an inappropriate definition due to the negative connotation of the term noise, as per its definition;

 “A sound, especially one that is loud or unpleasant or that causes disturbance”. 

The use of the term noise assumes, prior to the result of the assessment, that the noise/sound being assessed is ‘loud’, ‘unpleasant’ or ‘causes disturbance’, which is an assumptive term. However, the use of the term ‘noise’ is an apt descriptor as in most cases the purpose of a noise/sound assessment for planning purpose has been justified by either complaints received by a Local Authority, which is characterising the sound as unpleasant to the complainant. Or the analysis of an Environmental Protection Officer providing justification of potential effect on amenity, through an intrusive, unpleasant or disturbing noise. The IOA provided comment on the alteration during the consultation;

“The draft standard makes a distinction between sound and noise, it is unclear whether this is warranted or of any particular use in the application of the standard. Our members had mixed views on this. However, it is possible to imply from the draft that a sound cannot be a noise until it is rated adversely using the standard, which seems incorrect. The wording should be clarified in the final version.” (IOA 2014)

4.2.2 Evaluation & Discussion of the effect on the assessment

The alteration to the term ‘noise’ and ‘sound’ is a minor alteration and will have no effect on the assessment.

4.3 Preparation

4.3.1 Critical Review and Analysis

This section of the 2014 edition is new and is aimed at providing an emphasis on context within the investigation. It states the assessor should “gain a sufficient understanding of the situation”, this being in the form of an appraisal. This section is introducing the requirement for ‘proportionate analysis’, which in principle is allowing the assessor to provide a subjective analysis of the scenario based on the assessor’s opinion on the likelihood of impact and present a level of analysis proportionate to the expected level of impact. This will allow each scenario to be analysed in more detail, ensuring that appropriate justification is provided for assessment methods, such as, which sources are being analysed, measurement location and quantity, duration and timing of measurements. This will allow the uncertainty of a given scenario to be reduced and the accuracy of the assessment to be increased.

However, the allowance for a subjective approach in any technical assessment will allow for an increase in uncertainty from assessor to assessor.  It is assumed in all scenarios the assessor will be appropriately qualified to carry out the assessment. The emphasis in subjective assessment will be on professional judgement and the qualifications and experience of assessors, both of which could vary significantly. Not just from an academic/experience perspective but from a social aspect, for example the assessor may have experience of the effect on his/her amenity from a specific source. This could allow for a positive or negative impact on the assessment based on their experience rather than the context of the scenario. The presence of a subjective analysis is however supported by the advice presented within the Institute of Environmental Managements (IEMA) – Guidelines for Environmental Noise Impact Assessments;

“It must be remembered that the effects of noise are primarily subjective, and while it is desirable to include as much objectivity as possible into the assessment process in order to obtain consistency, there should be no concern in allowing professional judgement to come in the final analysis.” (IEMA 2014)


Further to this a study was carried out by Esta Rahno, on ‘How to assess objectively the effects of noise, when it is subjective?’ in his studies he emphasises that the perception of sound is profoundly subjective and surmises with the following statement;

“If noise is a subjective perception, then how is it possible to assess it objectively and mitigate road traffic noise impact on people? (Rahno, E)


This highlights the challenges in the assessment of sound and the likelihood of it presenting a potential negative impact on amenity.

This also emphasises the requirement for not having the assessment of impact criteria, such as, in the 1997 edition, as follows;

  • A difference of around +10 dB or more indicates that complaints are likely.
  • A difference of around + 5 dB is of marginal significance.
  • If the rating level is more than 10 dB below the measured background noise level then this is a positive indication that complaints are unlikely.

These criteria present a scale of impact which is objective and finite and is not applicable to the likelihood of complaints in the majority scenarios. The 2014 edition sets the criteria of ‘low impact’ when the rating level is below the background sound level, when considering the context. Thus allowing more flexibility from the author in the assessment. Because in some scenarios the context would allow the rating level to be marginally below the background sound level, and in other scenarios the rating level would have to be significantly below the rating level.

4.3.2 Evaluation & Discussion of the effect on the assessment

The following hypothetical example is provided to outline the importance of context; an area with a particular high background sound level could have industrial plant introduced that is +5dB above the background sound level. If there is no subjective assessment or consideration for context, then the assessment could be completed outlining there is ‘marginal significance’ which is, from a planning permission perspective, deemed satisfactory in accordance with BS4142:1997 and Local Authority guidance. However the assessment needs to take consideration for the introduction of sources in high risk/high noise environments (context), where slight increases in noise level will begin to present a considerable effect on amenity in the area. The justification for this is based on context and the subjective nature of the level of impact not being acceptably processed by an objective method of analysis. The application of context was first implied in the Wilson report which explained that it is well known that the actual loudness of a noise is not, by itself, a measure of whether it will give rise to annoyance or complaint. The reaction of the hearer is affected, for example, by the kind of noise, by the general level of noise already existing, by whether the hearer has become accustomed to it (HMSO 1963). The introduction of preparation and context aligns with the new assessment criteria which provides a simpler and more approachable assessment of impact from a contextual perspective.


The introduction of context does present an emphasis on the qualification and experience of the author. The use of context to allow the author to reduce or increase the level of impact is a precarious notion and will provide a wide scope for speculation between authors and reviewers. However it is agreed that a subjective assessment is essential, as when one is attempting to ‘quantify’ a human response, a human response is required to gauge it. Further research is required into the human response to industrial noise, with the aim to avoid speculation within subjective assessments and provide an appropriate objective method of assessment. The introduction of context will require each assessment to provide a more in-depth study in to the site to ensure the context of the site is appropriately considered. This will reduce the uncertainty of the assessment and improve the accuracy. This will impact on the result of the assessment, however this is not quantifiable, instead it will in turn be analysed from the application of the standard and the cumulated experience of the assessors over the coming years. When the focus is aimed at the qualification and experience of the author, which is requested to be outlined in reports within the new edition, this then presents the question; what is an appropriate level of qualification and experience? And how does one judge this? This could be an appropriate level of professional membership, however any professional membership can be brought in to doubt if the content of the report is brought into question. The same can be applied to qualifications. A solution to this is to provide a ‘BS4142 accreditation’ which an author will have to achieve to be able to be deemed ‘appropriately qualified’ to carry out an assessment. This type of system would significantly improve the quality and veracity of assessments and would provide a trustworthy platform for judgements to be made.

4.4 Instrumentation

4.4.1 Critical Review and Analysis

The requirement for the use of Class 1 sound level meters that comply with BS EN 61672 -1, for free field application. Filters that comply with BS EN 61260, Class 1, and sound calibrators that comply with BS EN 60942, Class 1. The 1997 edition required the use of, Type 2 or better conforming to BS EN 60804, for the monitoring of equivalent continuous noise level and required the use of, Type 2 or better of BS EN 60651.

The difference in Class 1 and Class 2 sound level meters is primarily characterised by the tolerances of the equipment and its components. All the components within a sound level meter have a tolerance from their centre point, these tolerances add up to provide a tolerance for the sound level meter. These variations dictate the accuracy of the equipment which ultimately allows the meter to be classified. The degree of tolerance is the difference between the classifications, for example the tolerance limits attributed to frequency weighting are defined by BS EN 61672 – 1. At the reference frequency of 1kHz, the tolerance limits for Class 1 are +/- 1.1dB and for Class 2 are +/-1.4dB. These tolerances increase towards the lower and upper ends of the spectrum, with deviation of +/-2.5dB and +/-3.5dB, for Class 1 and Class 2 respectively at 20kHz (BSI 2013).

4.4.2 Evaluation & Discussion of the effect on the assessment

The change in equipment specification allows an improved accuracy and thus a decreased uncertainty in measurements. This reduction in uncertainty will subsequently increase the accuracy of the assessment.

4.5 Measurement Procedure

4.5.1 Field Calibration Critical Review and Analysis

The 2014 edition has introduced a more detailed criteria for field calibration checks. The 1997 edition stated ‘check the sensitivity of the measurement equipment before and after measurements. Record the results of such tests’. This did not present or insinuate a scale of acceptability and was vague, it was assumed the assessor would raise concern if the post calibration was significantly varied from the pre calibration, however this is not explicit. The 2014 version has introduced a deviation criteria for measurements where a pre and post calibration with a deviation that exceeds 0.5dB should be treated with caution. Further to this it states; ‘where the drift is 1dB or more, the measurement chain ought to be fully investigated as this will have an effect on the veracity of the data’.

The reason for field calibration is that it provides you with knowledge and evidence of how your equipment measures and increases the reliability that your equipment is working correctly.  According to the International Laboratory Accreditation Company (ILAC) the purpose of calibration is:

To know the uncertainty that can be achieved with the measuring instrument

  • To confirm whether or not there has been any alteration of the measuring instrument that could create doubt about the results.

To improve the estimation of the deviation between a reference value and the value obtained using a measurement instrument, as well as the uncertainty in this deviation, at the time the instrument is actually used. (ILAC 2007)


The potential for calibration drift is dependent on both the equipment and environmental conditions. The equipment will have a higher likelihood of drift dependent on the level of use, for example if it is used extensively the calibration drift is likely to increase due to component degradation over time. The environmental conditions, such as temperature, moisture and vibration, are also likely to give rise to increased calibration drift. Evaluation & Discussion of the effect on the assessment

The impact this is likely to have on assessments may require the repetition of long term monitoring or reduce the frequency that long term monitoring is carried out. This is because the main contributing factor to calibration drift is long term monitoring. If the equipment is kept in a good state of repair and used within the manufacturer’s specifications the likelihood of calibration drift due to equipment degradation is low. However, the likelihood of drift during long term monitoring is high due to the period of time that the equipment will be most exposed to harmful environmental conditions such as temperature fluctuations and precipitation. If the use of long term monitoring is reduced this will reduce the accuracy of the background sound survey carried out because the quantity of data to provide a ‘typical’ background sound level is significantly lower. However the control over the environment from the assessor being present to note potential adverse impact on the background survey improves accuracy.

The use of a scale of calibration will only improve the accuracy of the assessment, as the level of uncertainty will be reduced.


4.5.2 Weather Conditions Critical Review and Analysis

The requirement for detailed documentation of numerous weather parameters has been introduced in the 2014 edition. The 1997 edition simply stated the following:

Record the weather conditions prevailing during all measurements.” (BSI 1997)


The standard goes onto to state that weather conditions can affect noise levels by influencing sound propagation or generating noise which can be pertinent to the assessment and more than one assessment may be appropriate. The requirements of the 2014 edition are outlined and discussed in table 4.2.

Record the weather conditions that could affect measurements. Monitor wind speed at the measurement location, using an anemometer, and record the wind speed together with the wind direction. Exercise caution when making measurements in poor weather conditions such as wind speeds greater than 5 m/s–1.
This criteria is similar to the 1997 edition, however it is explicit in the weather attributes that it requests. The parameters that are required all have a potential of influencing the assessment and it is therefore pertinent that they are disclosed. For example, it is necessary to note the prevailing wind direction along with the wind direction as this will influence the specific sound level at the receiver point.
Visually estimate cloud cover by eye as either a percentage of sky covered by cloud or in oktas. Record all forms of precipitation together with the period over which the precipitation occurred, having regard to how this might affect uncertainty (see Clause 10 and Annex B).
The criteria for cloud cover is only achievable for short term monitoring or at the beginning or end of long term monitoring which reduces its relevance. Precipitation was a requirement of the 1997 edition. The level and duration of rainfall will increase the noise level, there is no explicit statement as what percentage precipitation is regarded detrimental. IEMA’S guidelines state “Care should be taken… in particular, ensuring that the calibration is not compromised by cold or wet conditions”. (IEMA 2014)
Record the temperature at the measurement location, in °C, at the beginning and the end of the measurement period, and at any other appropriate time if there is a change in the weather conditions.
The temperature was not required to be noted within the 1997 edition. This will increase the validity of data whilst measuring in environments which are close to the extremes in which the equipment is operable. Temperature is unlikely to cause a significant affect, however it can cause localised focussing of noise. As discussed in IPPC H3;
”Temperature and humidity can affect the air absorption, although in practice these effects are often much less than those of distance, barriers, wind and the like and are unlikely to have a significant effect, especially at low frequencies. However, under some conditions, such as temperature inversions, sound propagation can become very complex and result in localised focussing of noise. Noise can also appear to be coming from above rather than directly from the source”. (EA 2002)
Where appropriate, use instruments for measuring meteorological parameters during long-term unattended measurements by means of a logging meteorological station at the measurement location.
The use of meteorological stations will in most circumstance provide detailed data of the effects of meteorological conditions and allow a more accurate depiction of the measurement location. This in turn will increase the validity of the background sound level and thus reduce uncertainty. This has implications in relation to its feasibility, for example secure long term monitoring locations are challenging to locate when considering locating a sound level meter alone, the introduction of a weather station alongside this could reduce the number of long term monitoring’s but in turn if short term monitoring is increased the control over the measurement environment is increased.
NOTE 1 Weather conditions can affect sound levels by influencing sound propagation or generating sound which can be pertinent to the assessment.
This point is retained from the 1997 version.
NOTE 2 Whilst regional weather forecasts are useful in planning when to measure, local conditions can often vary significantly from the regional forecast. Forecast ought not to be used instead of site measurements of the actual weather during the survey.
This point is explicit in relation to the inaccuracy of forecasted weather conditions. This again will increase the difficulty in attaining long term monitoring data due to the complexity of siting the equipment. This note is in direct contradiction to IEMA’s guidelines, which state;
“The more detailed the weather records, the better, but it will be rarely practicable to set up automatic logging weather stations to accompany the noise loggers, although such monitoring tends to occur as a matter of course for studies associated with windfarms. Wind speed and direction also can be highly localised near buildings and care is needed in locating monitors to avoid misleading data being collected. Often it will be more practicable to make a reasonable estimate of the effects of different weather conditions rather than attempt to measure them”. (IEMA 2014)
This therefore presents inconsistency between guidance, however the request in the 2014 edition is explicit in the requirement for localised meteorological conditions to be logged for the duration of surveys.
NOTE 3 It might be appropriate to make more than one assessment to account for varying weather conditions.
This point is retained from the 1997 version.
Annexe B of the 2014 edition provides further detail on appropriate considerations for weather considering the sources of sound and the transmission path.

Table 4.2 – Discussion of the requirements for weather conditions.  

The introduction of the use of meteorological station to be located with noise monitoring stations presents a challenge in terms of the feasibility of locating expensive equipment in unsecure locations. As stated by the ANC in their consultation response;

“There may be situations in which on-site weather monitoring may be helpful, and the assessors’ attention should be brought to the consideration of this possibility in some instances. Blanket application to all surveys, however, was broadly agreed to be excessive and to represent a significant and unnecessary burden in terms of cost and practicality”. (ANC 2014)

The IOA also showed concern with their consultation response;

“In general the more detailed measurement requirements will cost more, both in terms of monitoring / analysis time and equipment. For some investigations, the weather monitoring equipment required to fully comply with the standard will prove very expensive (possibly, thousands of pounds) which would be a disproportionate cost for small projects and projects with no real prospect of causing noise disturbance or where meteorology is unlikely to have a substantial effect on the outcome.” (IOA 2014)

As a result this may reduce the number of long term monitoring sessions, the purpose of which is to increase the validity of an assessments, yet the assessor will be directly contradicting the standard and presenting an increased level of uncertainty if detailed weather conditions are not presented alongside long term monitoring data. This is likely to increase the use of short term monitoring, which will reduce the quantity of data collection and therefore reduce the validity of the data, however the uncertainty will be decreased by the increased control over environmental conditions affecting the monitoring. This is confirmed by the IOA in their guidelines on Noise Impact Assessments;

“In the case of short term measurements, fewer data are normally acquired at a given location than would be obtained from monitoring for 24 hours or a week. However, the data may be more relevant and useful than data from a week’s continuous monitoring. Short term attended monitoring, if undertaken by a competent operator, can yield data about weather conditions and likely sources of noise. It is therefore possible to use that data to interpret results.” (IOA 2002)

Therefore this requirement appears to be questioning the reliance and reliability of long term monitoring, that is not verified by local weather assessment. Which is also outlined by IPPC in their Noise Impact Assessment guidelines;

“Thus by monitoring over a period of between several days and a few weeks, a larger data set can be obtained from which to determine the pattern of variation of sound levels and the values at different times of the day and week. However care should be exercised in interpreting this data. For example, long term monitoring may coincide with a period when weather conditions are inappropriate.” (EA 2002)

The measurement and/or calculation of the rating level should also consider the meteorological conditions. Specifically the prevailing wind direction provides a high likelihood of significantly affecting the rating level. Evaluation & Discussion of the effect on the assessment

The use of weather stations alongside long term monitoring, whilst contradicting other guidance, will present useful information and provide a more accurate depiction of the noise profile of an area. This will allow the assessor to present valid judgements on the effects of the weather on long term background monitoring, as well as the impact on the rating level. The statement from IEMA, that the localised weather conditions can vary significantly, is integral in the appropriate location and use of a weather station alongside the sound level meter. The likely impact on the assessment is an increase in accuracy and in relation to background sound levels will involve both long and short term monitoring to be carried out, to ensure assessors are fully compliant with the new requirements. Further to this the prevailing wind direction in an area will have to be understood, to outline the effect on the rating level.

4.6 Specific Sound Level

4.6.1 Critical Review and Analysis

The specific sound level section of the standard has largely remained the same between the editions. The main change is in the alteration of the night time reference time interval from 5 minutes to 15 minutes. 

This alteration will have an implication on the assessment of night time specific noise levels and will reduce the expected impact rating in the assessment of the rating level. No evidence has been presented for the reasoning behind the alteration in reference time interval, this point was questioned by the IOA in the consultation draft;

“It is proposed to change the night time reference period from 5 minutes to 15 minutes, which would make the standard less stringent for the assessment of night-time noise of limited durations. Since 1980, IOA members have considerable experience of using the 5 minute reference period, and see no need for this change”. (IOA 2014)


There is no justification for the increase in potential impact during night time, the World Health Organisations Night time Noise Guidelines, is an in-depth study into the impact of night time noise levels and it concludes that;

“Information about night-time noise exposure is relatively scarce, despite 10 EU Member States having limit values for night-time noise.”



“Further research on this topic is needed in order to gain an insight into the contribution of various noise sources to sleep disturbance.” (WHO 2009)

This evaluation questions the reasoning behind altering the reference time interval, when there is a lack of research to justify it.

4.6.2 Evaluation & Discussion of the effect on the assessment

The two versions of the standard are applied to the following hypothetical example to outline the impact of the change. For the purpose of the assessment we will consider that the context has been addressed and the standard objective rating method is going to provide the main analysis of the rating of the industrial noise source. The analysis is of an industrial compressor that operates for a total of 5 continuous minutes per hour throughout the night. The examples of the assessment for the 2014 and 1997 editions are shown in Table 4.3 and 4.4 respectively.

Measured Ambient Sound Level
LAeq,5min = 60 dB
Residual Sound Level
LAeq,5min = 50 dB
Background Sound Level (night-time)
LA90,15min = 41 dB
Night Time – Reference period 15 minutes

The total on time during the reference period is : 300 s

On time correction [to nearest 0.1dB as intermediate step in equation (4) calculation]
10log(300/900) = -4.7
Specific Sound Level
[10log(1060 – 1050) – 4.7] dB = 55 dB
Rating Level – (No Corrections)
55 dB
Background sound level
41 dB
Excess of rating over background sound level
14 dB
Assessment indicates
Significant Adverse Impact

Table 4.3 - BS4142:2014 Reference time interval example

Measured Ambient Sound Level
LAeq,5min = 60 dB
Residual Sound Level
LAeq,5min = 50 dB
Background Sound Level (night-time)
LA90,15min = 41 dB
Night Time – Reference period 5 minutes

The total on time during the reference period is : 300 s

On time correction [to nearest 0.1dB as intermediate step in equation (4) calculation]
10log(300/300) = 0
Specific Sound Level
10log(106.0 – 105.0) dB = 60 dB
Rating Level – (No Corrections)
60 dB
Background sound level
41 dB
Excess of rating over background sound level
19 dB
Assessment indicates
‘Complaints Likely’

Table 4.4 - BS4142:1997 Reference time interval example

The increase in the reference time interval during night time has decreased the rating value, and thus reduced the likelihood of impact. In the example provided in table 4.3 and 4.4 the impact difference is 5dB lower for the 2014 edition. This amount of variation in noise level has been categorised by the IOA Guidelines on Noise Impact assessment as, a variation of between 5.0 dB – 9.9 dB being ‘Substantial’ (IOA 2002). If the on time is increased to 15 minutes, and the example assessment is repeated then this would show the same impact rating for both the 1997 and 2014 editions.


In relation to the assessment, there is likely to be a decrease in the night time rating level due to the increased reference time interval, when the on time is ≥15 minutes, it appears that this has no basis of research. The WHO state that further evidence is required to ascertain acceptable levels of night time noise, therefore it would be a conservative approach to consider retaining the 1997 edition reference time interval to ensure amenity is not affected. In lieu of further research being presented to substantiate such alterations.

4.7 Background Sound Level

4.7.1 Critical Review and Analysis

The 2014 edition provides additional detail of appropriate analysis of background sound levels, a commentary is presented in section 8.1 that provides an outline of what the assessor is expected to consider. The IOA consultation response eludes to the fact that they believe assessors applying the 1997 edition would commonly consider a cautious approach and would use the lowest background sound level.

“The clarification in 8.1 that the background sound level should be “typical”, rather than the lowest measurable, and the advice on how to derive this value is welcomed”. (IOA 2014)

However, this is an assumption as the 1997 edition clearly states;

“Make measurements during periods when the background noise level is typi

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