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What is BS4142?

BS4142:2014 Methods of Assessment and Rating Industrial and Commercial Sound is an British Standard that describes a method to assess the impact of an proposed or existing commercial or industrial sound source. Its main purpose is orally to evaluate noise coming generated by new or modified commercial or industrial buildings or to support the application for a building permit or to determine the level of the impact of noise that may give the cause of complaints. For either of these an existing or potential noise maker will likely be told “you must have to have a BS4142 analysis’.

What exactly does an BS4142 assessment look like?

In essence, a BS4142 evaluation is a method for rating the impact of noise by comparing the noise of the source that is being evaluated (the specifically assessed noise) and background noise that would be present without the source. The particular noise is corrected by acoustic features by imposing the decibel threshold for impulsive or tonal content as well as other characteristics that are easily identifiable in the background acoustic. The level of noise that is corrected is known as the “rating level”. It is meant to reflect people’s general reactions to noise, where the noise that has these features is perceived to be more annoying than noise without features at the same degree. The rating level is also a part of the same correction when the noise source doesn’t run in a continuous manner.

It could be necessary to determine the exact noise when the other noise is at a minimum, to give an accurate picture of what the actual level. Sometimes, it is necessary to account for other noises by determining their contribution to the source of noise and then adjusting the measured noise level in line with it. This allows for an accurate picture of the particular noise free of other noise sources. The exact noise is measured by using the dB LAeq Noise measurement index. It is essentially an average of the noise measured over the measurement time.

In contrast to source noise, background noise is measured with the decimal LA90 Noise measurement index. This is the level of noise that was exceeded for 90 percent of the measurement time and, if it’s over the minimum threshold, it is the constant noise that is absent from or other causes. To determine your background noise level, tests need been taken without source noise being heard or, alternatively, in an location where the environment is not affected by the source noise, and is otherwise identical to the location where source noise is heard.

It is normal to take repeated measurements of background noise because it is prone to fluctuation in the course of the day, especially at night, or even between different times during the day. It can also change with the direction of wind as well as other meteorological elements. Therefore the measurement equipment might require being kept in a safe environment that is representative of the area that is of particular interest, so that it can record consecutive measurements of an dB LA90 value. The BS4142 states that the measurement time is not less than 15 minutes. It also states that the purpose is to measure the typical values during specific intervals of time. It offers an illustration of statistical analysis in which the’modal’ level (the frequency at which it occurs) is deemed to be ‘typical’. To get the most data to be used in research, most short period permitted by BS4142 is to be utilized as a result. Measurements typically take place using the 15-minute measurement interval.

What is the impact of noise evaluated?

When the exact noise level, adjusted by acoustic effects and the typical background noise levels, applicable to the operation time of the source have been determined and compared, the two levels are then the two are compared. The BS4142 specifies that:

A) In general, the larger the difference, the more the the impact.

B) A variation of 10 dB or greater could be a sign of an impact that is substantial in the specific context.

C) A variation of approximately 5 dB could be an indicator of an adverse effect, based on the situation.

d) The less the rating is in relation to the background sound level the more likely that the sound source will have an adverse effect or a significant adverse effect. If the rating level is not surpass the level of background sound it is an indication that the particular sound source is having a small impact dependent on the situation.

The most important thing to remember is the fact that professional judgment is expected from an acoustic expert because something that is an indicator of high impact in certain circumstances might not be in the same way under different circumstances!

Noise volume

The BS4142 says that for any difference in rating level and background level of sound, the extent of the total impact may be greater in an acoustic setting in which the level of residual sound is high than in an acoustic space in which the level of residual sound can be low’. Particularly, when background level of sound and rating are low, the levels could be just as, or even greater as the margin at which the rating level is higher than those of background’. This means that when certain noise ratings are low, such as less than 35 dB LAeq, there is no requirement for a background noise study to show that there is a minimal impact.

In addition, it declares that “when residual sound levels are extremely high the residual sound could cause negative or substantial adverse effects and the amount between the rate level and the background is higher than the background may indicate the extent to which a specific source of sound could make those impacts worse’.This implies that in highly noisy areas there could be a requirement that specific noise levels to at least 10 decibels below the background noise.

The story of BS4142’s history

The methodology in BS4142 first appeared in the “Wilson Report” in 1963(!) at Appendix 15: Simplified Methodology for Assessing Reactions to Industrial Noise in mixed Residential or Industrial Areas. In the Wilson Report itself, which includes its final document of the Committee on the Problem of Noise worth a attention because it signals the first steps towards recognizing noise as an important environmental issue. In this initial method, the exact noise level is compared to the amount of noise that is expected to be present in a particular setting, using various variables, such as the frequency at which it is experienced and the kind of space, instead of the background noise, which was introduced in the initial British Standard version in 1967.

BS4142:1967, Method for rating industrial noise that affects mixed industrial and residential Areas The standard clearly shares an identical title with that of the Wilson Report Appendix but it provides a comparison between the noise level that is specific to the actual background noise level. The latter was found as being the level that was exceeded for 90 percent of the time, or a “notional” background noise level that was determined by the characteristics of the region. The correction for impulsive or tonal noise was incorporated into the Wilson report, and the standard remained in effect until the year 1990.

The BS4142:1990 version had the same name however it was referred to as “method of rating” …’ instead of’method to rate’. …’. This distinction isn’t described! The method was not changed fundamentally , but more details were added to make it more current The notion of a “notional” background noise levels was eliminated and reference was made the use of sound level meters to determine the level of background noise directly, such as an LA90 as well as the particular noise was referred to as an LAeq as well, both of which were possible with the help of the portable devices for sound level measurement during the interim.

The BS4142:1997 standard was continued using the same name and method similar to 1991’s, but there was a major defect in the 1990 standard was rectified, in which the specific noise measured was corrected for additional “other” noise (referred to as residual noise) by subtracting the LA90 value of the noise instead of the LAeq. The majority of noise experts did this properly in the time between but we are certain that those who advocated for it at Public Inquiry, and in the courtroom, would have enjoyed this procedure until it was rectified.

BS4142:2014 included some important updates to the version of 1997, including an introduction (and content) which replaces “noise” with the word “sound’ as well as introduces the concept commercial sound, and updates the corrections to acoustic characters (+5 dB for tonal or uninhibited content, and when the noise in question is not consistent enough to draw the attention of) which were unchanged from the appendix in 1963!

The standard is in the process of being developed.

It is in the process of being reviewed as to whether additional updates are needed, e.g. how the character corrections may be actually added together (one of the changes made in the version of 2014) and if it is appropriate to assess subjectively the impact of the character instead of having the entire thing based on measurement.

What’s clear from the recent discussions on the contents of the most recent edition is the ultimate decision about the impact is dependent on the context and judgement of a professional. This is in line with the original idea that was outlined in the Wilson Report Appendix which was to consider the circumstances of the noise for example, whether it came an entirely new or newly constructed factory or one that existed for a short time in an unusual environment or an established factory that was in line with the region; and the kind of zone it was located in (rural through urban residential to industrial heavy) was crucial to the evaluation.

One aspect that is being discussed is whether the method in its current form has the accuracy that one would think of from an established standard. It certainly differs from the standards utilized to regulate such things like sound insulation testing as well as the testing of wind turbines’ acoustics.