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What does a BS4142 assessment involve?

BS4142:2014 Methods of rating and assessing Industrial and Commercial Sound is an British Standard that describes a method for assessing the effect of an proposed or existing commercial or industrial sound source. Its main purpose is in assessing noise 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 noise that could give the cause of complaints. For either of these the potential or current noise maker will likely be told “you must have to have a BS4142 evaluation’.

What is an BS4142 assessment look like?

The essence of a BS4142 test is a method of rating the impact of noise using a comparison of the noise coming from the source that is being evaluated (the particular noise) as well as the background noise that would be present without the source. The noise that is being assessed is ‘corrected by acoustic features by introducing 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 called the “rating level”. It is designed to reflect the general reactions to noise, where those with features are perceived to be more annoying than non-featureless noise at the same degree. The rating level is also a part of an equivalent correction if the noise source doesn’t run in a continuous manner.

It is possible to determine the exact noise at a moment when the other noise is at a minimum, to give an accurate picture of what the actual level. Sometimes, it is necessary to accommodate for the other noises by determining their contribution to the source of noise, and then correcting the measured noise level in line with it. This allows for an accurate picture of the noise in question, not influenced by other sources. The exact noise is measured by using the dB LAeq Noise measurement index. This is basically an average of noise over the measurement time.

Contrary to source noise background noise is measured by using the decimal LA90 Noise measurement index. It is the amount of noise that was exceeded for 90 percent of the measurement time and, if it’s higher than the minimum, it represents the continuous noise that is present in the absence of or other causes. To determine your background noise level, tests need to be taken with no source noise being heard or at an location where the surroundings are not affected by source noise, and is otherwise exactly the same location as the source noise is heard.

Typically, it is essential to take repeated measurements of background noise because it is prone to fluctuation especially between day and night, or even between different times during the day. It could also be affected by the direction of wind and other meteorological variables. Therefore the measurement equipment might require being kept in a secure location that is representative of the area of interest, in order to record each time the decibels LA90 value. The BS4142 specifies that the measurement time must not be shorter than 15 minutes, and the goal is to determine the typical values during specific intervals of time. It gives an instance of statistical analysis in which the’modal’ level (the one that is most frequently observed) is considered to be typical. To get the most data to be used in statistics, only the shortest time permitted by BS4142 is to be utilized as a result. Measurements generally take place with the 15-minute measurement interval.

What is the impact of noise evaluated?

When the exact noise level, adjusted for acoustic characteristics and the typical background noise levels, which are relevant to the operating time of the source are established The two are then evaluated. The BS4142 specifies that:

A) The more the difference, the more the the impact.

B) A variation of 10 dB or more could be a sign of an impact that is substantial depending on the situation.

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

d) The lower the rating level in relation to the background sound level and the lower it is, the less likely that the particular source has an adverse effect or a significant adverse effect. When 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 setting.

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

The concept of absolute noise degree

The BS4142 says that for any difference in rating level and background noise level extent of the impact could be higher in an acoustic space in which the level of residual sound is high than in an acoustic space in which the level of residual sound has been reduced’. Particularly, when background level of sound and rating are low, the levels may be equal to or even greater as the margin at that the rating level is greater than those of background’. This basically means that if certain noise ratings are low, such as less than 35 dB LAeq, there is no requirement for a background noise survey to prove the impact of noise.

However, it also declares that “when the levels of residual sound are quite high there is a possibility that the residual sound will cause negative or substantial negative impacts The margin between the rate level and the background surpasses that of the background could provide an indication of how much the specific source of sound could make those impacts worse’.This means that in extremely noisy regions there could be a requirement that specific noise levels to be at least 10 decibels lower than the existing noise.

The history of BS4142

The methodology in BS4142 first appeared in the “Wilson Report” in 1963(!) at Appendix 15: Simplified Procedure for assessing the Reaction of Industrial Noise in mixed Residential as well as Industrial Areas. This is found in Appendix 15, Simplified Procedure for Assessing Reaction to Industrial Wilson Report itself, which is its final document of the Committee on the Problem of Noise worth a noting because it marks the first steps towards recognizing noise as an environmental issue. In this initial method, the noise level is compared to the amount of noise that can be expected in the particular environment with various modifications, including the frequency at which it occurs and the nature of space, instead of the background noise, which was first introduced in the British Standard version in 1967.

BS4142:1967 Method of measuring the impact of industrial noise on 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 level of noise that was specified and the background noise level. The latter was found as being the levels that were exceeded for 95 percent of the time or a hypothetical background noise level, which was determined by the nature of the region. The correction for impulsive or tonal noise was adopted from the Wilson report, and the standard remained in effect up to 1990.

The title BS4142:1990 was the same however it was referred to as “method for rating” …’ instead of’method to rate’. …’. This distinction isn’t discussed! The method was not changed in any way, however more detail was added to keep it current The notion of a “notional” background noise 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 identified as an LAeq as well, both of which were feasible with the portable devices for sound level measurement over the interim.

The BS4142:1997 standard was continued using the same name and method that was used in 1991, however there was a major error in the standard of 1990 was fixed, and 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 court, might have been having fun with this before it was fixed.

The BS4142:2014 version contained significant changes to the version of 1997, including the title (and content) that replaces “noise” with the word “sound’ and introduces the concept of commercial sound, and revises the corrections for acoustic characters (+5 dB for toneal and uninhibited content, and when the particular noise is erratic enough to draw the attention of) which were unchanged from the appendix in 1963!

The standard is in the process of being developed.

This version is being reviewed to determine what future 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.

The most evident thing from the recent debates on the substance of the new revision is that the ultimate decision on the impact of a noise is largely based on the context and judgement of a professional. This is similar to the original concept 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 a factory that was in operation for a couple of years in an unusual environment or an existing manufacturing facility that was typical of the region; and the kind of area 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 procedure as it is written has the precision one would be expecting from standards. It certainly differs from the standards utilized to regulate such things like sound insulation testing, and the testing of wind turbines’ acoustics.