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Noise Induced Hearing Loss Claims: Sounding a Note of Engineering Pragmatism

Medico Legal

by Ed Clarke Managing Director at Clarke Saunders Acoustics

Feckless vs Fraudulent

Despite the risk to hearing of workplace noise exposure having been recognised for over half a century, a vast number of employees have had their hearing damaged unnecessarily by careless, thoughtless or just plain feckless employers. On the other hand, of course, for a while referred to as ‘the new whiplash’, the intangible and somewhat abstract nature of noise as a pollutant makes it an attractive target for exaggerated, perhaps even fraudulent claims.

In the vast majority of cases, appointed as a single joint expert to the Court, the acoustician is freed from any concern they may harbour over the merits of their client’s case, and is simply looking to convert the evidence presented into an estimate of the most likely noise exposure, on the balance of probabilities, to the best of their experience, skill and judgment. We are effectively providing a translation service, translating witness statements written in English to engineering reports in the mystical language of decibels.

The vagaries of an exact science

In very, very, very few cases is it possible to establish an individual’s noise exposure exactly. Even when presented with the most comprehensive evidence bundle including contemporaneous workplace dosimetry surveys and detailed working hours logs, assumptions and estimates still need to be made. Did the Claimant do exactly the same job as the worker who wore the dosimeter during the survey? Could that single day be taken to be representative of the whole employment period (often decades)? Did processes, plant and tools change over the period of employment?

In most cases recourse also has to be made to experience of similar workplaces, similar plant and machinery or published sources of information to which reference can be made. Imprecise, or conflicting evidence on a host of aspects, including working hours, the provision of hearing protection and the number of other concurrent noisy activities for example, serve to further broaden the range of uncertainty inherent in these assessments.

And these issues are exacerbated to a greater extent by missing records or fading witness memory, the further back in time the expert needs to cast for recollections, evidence or reliable published data.

At home on the range

In order to present information which is useful to the Court (or to the parties agreeing not to go to court) we must provide an estimate while being honest and transparent about how precise this information can be assumed to be.

At CSA we have established a methodology that sets out a range of noise exposure values rather than quoting a single figure as the output of any given piece of analysis. The better defined the evidence and data available, the narrower the output range from the analysis is likely to be, and this at least enables us to provide numerical analysis results without implying an inappropriate degree of precision.

We have refined this approach following feedback (both informally and in response to Part 35 questions) and in discussion with other practitioners in the field. An experts’ working group and industry best practice guide are long overdue. For now, I have set out a description of our process to enable instructing solicitors to appreciate our workflow, constraints and some of the challenges involved.

The Instruction

At the very outset we need to ensure we have the resources and expertise available to accept. We are fortunate at CSA, having seven highly qualified and experienced experts available, with data on file and experience going back to the early 1970s in a wide range of industries, so there isn’t much we haven’t come across before. We take the timescales very seri ously too. Especially those imposed by a Court Order.

Our experience to date suggests that the timeline around the claim process aligns pretty well with the reporting availability we are able to offer, with an instruction to reporting lag in the order of six months. We deliberately build quite a lot of flexibility into this system, however, to enable us to respond to short notice matters from time to time. This has been happening more often of late, perhaps I should n’t have owned up!


In most cases the evidence submitted leaves us some way short of all the information we would need to estimate noise exposure levels. We can establish an awful lot more with reference to our files, our memories and our textbooks, and talking to each other is one of the most valuable parts of our information gathering phase. Sometimes one of our experts is specified in the instructions by name, sometimes the instruction leaves that up to us. Almost invariably we will want to discuss it with someone older, or wiser, or indeed younger but with more recent experience of the noise source in question.

We’ve encountered an awful lot of different types of noisy (and some not very noisy) working environments and read even more descriptions of them from employees often using very specific colloquial references or with fading memories of tool or equipment names. Equating the terms windy gun, windy hammer with the same tool as a pneumatic chipper for example, or indeed a caulking gun in the shipbuilding industry requires knowledge and understanding beyond the realm of simple ‘analysis by word association’ and is greatly assisted by having had a direct aural experience of the industry and activity in question.

If a Claimant used a lathe, or a hammer, we don’t just look for noise data for ‘lathe’ or ‘hammer’, we need to consider how big a tool it was, used for what purpose, machining (or striking) what material and to what end.

One potential for concern with this collegiate approach, that we have turned into a big positive, is consistency. To ensure that each expert is tackling the assessments in the same way, using the same reference sources and materials, we have two dedicated engineers who act as moderators, comparing all of our NIHL output and curating a large (and growing) database of reference materials. These approved references can then be cited in our reports and quickly accessed if required, for example in response to Part 35 questions.


Some of the above data can be established from information in the particulars of claim. Sometimes (but not always) this is then augmented when we are issued with the Claimant’s witness statement. As this generally arrives only a couple of weeks ahead of our reporting deadline we are usually well into the analysis phase by this point, using proxy data that we’ll substitute back for anything more accurate that comes along.

We construct a noise exposure model of each episode of the Claimant’s employment, accounting for the working days and hours, including break times, transitions and any peripatetic activity. Due to the nature and order of evidence presentation, we tend to start with the Claimant’s version of events (which is generally the more detailed) and work through this, identifying and flagging any aspects of the Defendant’s evidence which is contradictory, or presents a different version of events in some way. These differences are then either flagged as a potential source of uncertainty (our reports include a chapter entitled ‘uncertainty’, which we feel is very important) or singled out for a specific sensitivity test (see below).

In some, relatively rare, situations both parties present equally detailed but conflicting versions of events. In these cases, we present the versions alongside one another to show differences clearly and transparently. At all times we are at pains to ensure the evidence presented to us is ‘translated’ as fairly as possible with out bias towards either party.

There are numerous aspects of these calculations which require assumptions or estimates on the part of the expert which we seek to do reasonably and most importantly do so making clear file notes and references in our calculations. As an example, if a Claimant was exposed to a wide range of noise levels using different tools throughout the day, and says they wore hearing protection for about 10% of the time, the result of the analysis will be very different if we assume that to have been a random 10% throughout the day, as opposed to the (much more likely) scenario of using the protection when engaged in the activities that seemed noisiest – which constituted about 10% of the work day. As long as we state our assumptions clearly, if either party has an issue with the view we have taken it is easy for them to raise as a Part 35 question.

Sensitivity Tests

Sometimes the expert will see two interpretations as equally likely or be responding to a difference or contradiction in the evidence. Where this refers to a single variable in the analysis – for example whether the Claimant worked 2 or 6 hour of overtime per week, we perform a sensitivity test by keeping everything else in the model static and varying only this parameter. This enables us to put this variable into the context of our assessment to show that it makes XdB difference to the result. This has been an especially useful way to address matters which appear to be a significant bone of contention between the parties, but when considered objectively do not make a significant difference to the output of the analysis.

Report - worth the paper it’s written on?

All of the research and analysis is for nought if we can’t get it across in our expert’s report. This needs to be sufficiently detailed to demonstrate how the analysis has been conducted and that all the key evidence has been considered. But not so long and confusing that no-one is able to wade through all the equations and acoustics mumbo jumbo. In fact, as a rule we try to keep algebra out of our reports altogether. We have them ready if you want to ask Part 35 questions about t h em though!

Our reports will set out clearly the assumptions we’ve made in our analysis and the ranges of input noise data we have used for our calcs. There’ll be a chapter on uncertainty, explaining what we don’t know as well as what we do, and any sensitivity tests will be presented in the context of the overall calculations results and conclusions to present this information contextually.

The analysis outcomes will generally be presented as a range of values, both for the daily noise exposure estimates and career noise dose totals, within which we consider the truth to lie, accounting for the uncertainty inherent in the process.

Please don’t ask us to choose one particular number within that range as the most likely result, as this rather undermines the purpose of defining a range in the first place – to set the results of our analysis on the context of the precision with which it is possible to make this estimate.

Right at the start of the report we’ll have reproduced our instructions, the evidence we’ve been issued with and the specific questions we have been asked. So, as we write the conclusions we go through these one by one and make sure we’ve answered them.

And then there’s the killer question!

In your expert opinion…

On balance of probabilities…

Considering the prevailing guidance and date of knowledge…

Was the defendant negligent?

And this is where we have to reel our necks back in ever so slightly. Negligent is one of those words with special powers, nuisance is another. Not in the Harry Potter sense, but in that it would be for others (i.e. the Court) to make that judgment.

So, we look for a form of words which sets out the circumstances under which, and the reasons why, based on the results of our analysis, the Court could find the Defendant(s) to have been negligent. We aren’t shirking our responsibility to the Court, we are simply recognising our role in the proceedings.

We’ve done an awful lot of these assessments now, and we think the assessment process, reporting format and quality assurance systems we have in place are pretty good. But in the spirit of Continuing Professional Development, every day is a school day and an opportunity to learn and get better – all suggestions gratefully received. And volunteers for that best practice working group?

Many thanks to Ed Clarke and all at Clarke Saunders Acoustics.

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The CSA Centre of Acoustic Excellence

Acoustics specialist Clarke Saunders Associates is upholding a family and business tradition with the election of company director Dan Saunders to a key national association role. Dan has been appointed chair of the ANC, the Association of Noise Consultants, which represents the acoustics and noise professions across the UK.

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