Noise Immission Level (NIL) – Part 3 – more complicated features

This third article in relation to the Noise Immission level (NIL) considers some of the more complicated or arguable features. The first article considered the basics of the NIL. The second article considered how the Coles guidelines use the NIL.

Notches/ bulges between 10 – 20 dB with a NIL between 90 and 100 dB (A) NIL

As covered in the second article, the Coles guidelines set out two different levels in relation to the notches/ bulges and the NIL that is required.

For a R2 (a) case: a 10+ dB notch/ bulge will require a NIL of 100 dB (A) NIL or more.

For a R2 (b) case: a 20+ dB notch/ bulge will require a NIL of 90 dB (A) NIL or more.

On the face of it, the combination of audiometry and NIL either results in a Coles ‘pass’ or not.

However, what happens if the notches/ bulges are somewhere between 10 – 20 dB and the NIL is between 90 – 100 dB (A) NIL?

However, it is potentially arguable that different permutations may also support a NIHL diagnosis.  If a claimant has a NIL of, say, 95 dB (A) NIL, there must be a point at which a notch/ bulge is sufficiently large for a diagnosis of NIHL?

This might be especially arguable in a ‘near-miss’ case. For example, where the notch/ bulge is, say, 18 or 19 dB (so almost a R2 (b) level) and the NIL is, say, 98 or 99 dB (A) NIL, so almost at a R2(a) level. 

It could be argued (and is sometimes argued) that this is not ‘against’ Coles but rather it is an interpretation of the guidelines. Of course, the guidelines suggest some interpretation can be done by medical experts.

Conversely, if there was a NIL of, say, 91 and a notch/ bulge of only 11 or 12 dB, this would seem to be too far away from the guidelines to be arguable.

However, in a case where the bulge is even greater than 20 dB (say 30 dB), I believe that it would be difficult to argue that an even lower NIL than 90 dB (A) NIL would be needed.  It seems likely that with such a relatively low amount of noise exposure, with the presence of a very large notch/ bulge that would point away from NIHL completely. An alternative diagnosis might seem more likely.

Likewise, I do not believe that if there was very high NIL, say 110 dB (A) NIL, the bulge could be reduced.  This would call into question whether the audiology itself supported a diagnosis of NIHL.

Ultimately, whether this is arguable will be a matter of judgement for the medical experts and a party’s legal representatives, based on the facts of any one case.

Averaged Audiograms and R2(b)

The second article in this series highlighted that Note 3 of Coles allows the 10+ dB notch/ bulge required in a R2(a) case to be reduced by 3 dB (so to 7+ dB) on averaged audiograms.  Whether audiograms can be averaged can be a source of controversy in itself.

However, there is no corresponding assistance of how this should be applied to R2(b) cases, or indeed whether it can be at all.  Should there be a reduction for averaged audiograms to 14+ dB (or 17+ dB) from the 20+ dB notch/ bulge needed on a single audiogram.  Again, this is a point which is arguable (and is sometimes argued).  It depends in part on the facts of the case.  

It will be a matter for each medical expert as to whether such a reduction (and to what level) can or should be made in R2(b) cases.

Expert engineering evidence results in a NIL which ‘crosses’ one of the NIL limits

The next feature which can sometimes cause confusion is when an expert engineer calculates the NIL and rather than calculating a precise figure, gives a range. For example, a conclusion that the NIL is between 95 – 102 dB (A) NIL.

The first thing to consider whether this might be resolved on the facts of the case.  

For example, if a claimant was exposed to a particular instantaneous noise level, if the duration of his/ her exposure was found to be longer or shorter on a daily basis, this would have an effect on the daily noise level – and in turn the NIL.  So there might be a factual dispute as to whether a claimant used an angle grinder for, say, 1 or 2 hours per day.  This previous article may be of interest in this regard.

Likewise, there might be a dispute as to the number of years that exposure occurred.  This could be a simple matter of when a claimant began/ finished a particular role, or it might be a dispute as to when hearing protection was introduced.

What if there is a range which cannot be resolved on the facts?

However, the engineer may simply say that the exposure to noise cannot be accurately calculated on daily basis, and so the NIL falls within a range also. This, of course, may result in difficulties for the daily noise level and breach of duty, but it may also cause difficulties for the NIL. 

Although engineers are sometimes reluctant to try to calculate a ‘mid-point’ of the range, in my experience lawyers and judges tend to take a more pragmatic view.  It seems reasonable to take the view that the actual NIL is less likely to be at either end of the range but more likely to be somewhere towards the middle. 

What should be considered that is that the decibel range is not an arithmetic scale, but a logarithmic scale.  Therefore, the engineer should be asked to consider where the mid-point lies, rather than lawyers simply taking the arithmetic mid-point.

Daily noise levels below 85 dB (A) lep,d being included in the calculation for NIL

This is something which is suggested should not happen by Note 7 of the Coles guidelines. 

However, it is sometimes argued nonetheless and again, it may be a question of degree. If there was, say, a daily noise level of 84 dB (A) lep,d, this might be something that is arguable (and something which is from time to time is argued).

I would suggest, however, the default position is that Coles suggests that this should not happen.  There would have to be a strong argument to include any daily noise exposure of less than 85 dB (A) lep,d in such circumstances.


The three articles in this series, I hope, show the importance of the NIL in NIHL cases.  Of course, it is necessary for a claimant to prove the NIL based on his/ her actual exposure.  If a claimant fails to come up to proof, then any calculations in the engineering experts report as to NIL will be invalidated and so the case is likely to fail.

So in any NIHL case, practitioners should not just concentrate on the audiology and noise exposure/ breach of duty, but also consider whether the NIL supports a diagnosis of NIHL.  

“The exposure needs to be noisy enough for long enough.”

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