As the industry standard for assessing industrial and commercial sound, to say BS 4142 has a wide reach would be an understatement. With fundamental changes in the approach taken by the standard, it’s worth considering the impact this will have on those who carry out the assessments, those required to review them, and those that need them.

The latest revision to BS 4142 is a substantive rewrite of the standard, and to go into all the various changes would require a much longer article than this. Instead I want to look at what is probably the most fundamental change – the change from a conclusion based on some simple arithmetic, to contexts, uncertainties, and the reliance on knowledge and experience.

In my mind, BS 4142:1997 was about whether the difference between two numbers met the target. If it did, great; if not, mitigation needed to be explored to achieve the target difference. The 2014 revision, however, takes a different approach. A range of differences are likely to be calculated, the uncertainty present in the differences needs to be considered, and whether the differences are significant or not depends on the context.
To deal with this, throughout the process the assessor is required to rely on their experience and knowledge (both of their discipline, and the project in hand) to decide what is appropriate, and justify this to be the case. This ranges from determination of representative background noise levels, to the range of corrections for character now available when calculating the rating level. In fact, the emphasis is placed so heavily on the abilities of the assessor, it is now required that they state in the report why they believe they are competent to carry it out in the first place.
 
As there are a number of decisions to be made along the way, I envisage a much greater level of cooperation between the assessor and recipient as being essential. This will obviously make for an interesting situation when there are multiple interested parties. It may be that resources could be developed in the future to help add a degree of uniformity to the process, such as databases of sources, case studies to illustrate the effect of context etc.
Anything of that nature is clearly some way off, and in the meantime it will be interesting to see how the industry responds to the changes. Generally speaking, people aren’t always enthusiastic at the prospect of change, and I expect the new approach is likely to divide opinion. There will always be naysayers in every walk of life, but it’s my hope that the vast majority of us will see this as an opportunity for an improved process and rise to the challenge.
 
For those looking for more information, there is a good article in the Institute of Acoustics Bulletin Jan/Feb 2015 under the Technical Contributions section that goes into the background and changes in a lot greater detail. This is definitely worth a read, depending on your context.