As disease practitioners will be aware, causation is one of the major battlegrounds in NIHL claims.

The ‘Guidelines on the Diagnosis of Noise-Induced Hearing Loss for Medicolegal Purposes’ (2000) by Coles, Lutman & Buffin (“CLB Guidelines”) have been widely used, and accepted by courts, in diagnosing NIHL. One of the requirements to be met under those guidelines is R2, requiring a Noise Immission Level (“NIL”) of 100dB(A) to be satisfied if the audiometric evidence satisfies R3(a) with the authors noting that this level of noise being sufficient to cause hearing loss in 50% of individuals exposed to an NIL of 100dB(A). For those individuals who are more susceptible to noise damage, an NIL of 90dB(A) is required provided the audiometric evidence satisfies R3(b).

Increasingly, claims are presented by claimants in which medical experts are placing reliance on the ‘Guidelines for Diagnosing and Quantifying Noise-Induced Hearing Loss’ (2022) by Moore, Lowe & Cox (“MLC Guidelines”). One aspect of these guidelines is that the authors advocate that a Noise Immission Level (“NIL”) of 90dB(A) is sufficient to meet R2 for cases involving steady broadband sounds and 86dB(A) for cases involving non-military impulsive sounds. This is at odds with the CLB Guidelines.

In a recent case, Paul Cook v Ketson Plc, unreported, judgment was handed down on 18 December 2024 by Recorder Evans sitting at the County Court at Coventry, in which there was a dispute between the medical experts instructed respectively on behalf of the parties as to which audiogram should be used for diagnosis and the NIL required for R2 to be satisfied, the claimant’s expert proposing the MLC Guidelines and the defendant’s expert the CLB Guidelines.

Which audiogram to be preferred?

There were three pure tone audiograms available displaying the following results:

Right ear

Left ear

The claimant’s medical expert, Mr Zeitoun, and the defendant’s medical expert, Mr Green, were initially of the view that the January 2023 audiogram should be used for diagnosis as it was the most reliable in light of the Cortical Evoked Response Audiometry (“CERA”) testing. However, it was revealed shortly before the trial began that the claimant had in 2022 metastases from kidney cancer and had received chemotherapy in April 2022 until at least April 2024. Both experts agreed that the chemotherapy rendered the January 2023 audiogram unreliable and therefore should be disregarded for diagnosis.

Mr Zeitoun argued that the March 2021 audiogram should be preferred as it was the first audiogram, the CERA test supported the first audiogram, and the March 2022 audiogram (the audiogram with the better thresholds, which was accepted by Mr Zeitoun) was inaccurate with him speculating that the claimant’s tinnitus may have interfered with the test.

Mr Green argued that the March 2022 audiogram should be preferred on the basis that an audiogram with the best thresholds is generally regarded as the most reliable. He accepted that usually it would be appropriate to use the earliest audiogram as hearing deteriorates over time and therefore the earliest audiogram will usually have the best thresholds. This did not apply in this case and there was no good reason to disregard the August 2022 audiogram.

The judge preferred Mr Green’s evidence as it was “logically more understandable and more credible” and found that the August 2022 audiogram should be used for diagnosis.

The NIL required to satisfy R2

Engineering evidence had calculated the claimant’s NIL to be 96.8dB(A).

Mr Zeitoun relied on the MLC Guidelines and argued an NIL of 90dB(A) was required for all audiograms.

Mr Green argued that an NIL of 100dB(A) was required as the August 2022 audiogram satisfied R3(a). It was accepted that an NIL of 90dB(A) was required for the March 2021 audiogram. As the judge found that the August 2022 audiogram was to be preferred, an NIL of 100dB(A) was required. 

The judge noted that the CLB Guidelines were based on the balance of probabilities as an NIL of 100dB(A) will cause at least 50% of individuals to suffer hearing loss.

Mr Zeitoun argued that an NIL of 90dB(A) should be considered sufficient on the balance of probabilities because the CLB Guidelines ignores 50% of the population. 

The judge rejected this argument and noted the MLC Guidelines requirement of 90dB(A) is based on a result which showed that only 10% of those exposed to an NIL of 90dB(A) will suffer hearing loss. The judge found that the MLC Guidelines did not meet the balance of probabilities:

What this means for you?

This is an area which is likely to be the focus of further litigation as claimants increasingly seek to rely on the MLC Guidelines. This decision demonstrates that courts will likely be reluctant to deviate from the CLB Guidelines which have been tested over a number of years by both experts and in the courts.

The case also highlights an issue which practitioners face as to which audiogram to prefer with the court finding that the audiogram with the better thresholds should be preferred. This is logical as an individual cannot feign better hearing that he has. When faced with multiple audiograms, the audiogram with better thresholds is likely to be the most accurate.