Can Noise Exposure Cause Latent Damage?


A judgment handed down today in the case of Ross v Lyjon Company Limited (23rd September 2016 Liverpool County Court) raised important causation issues in relation to NIHL and reaffirmed the basic tenant of tort law, that it is for the claimant to prove damage.  

The case run by Roberts Jackson solicitors saw evidence from Professor Moore and Mr Zeitoun for the claimant and Professor Lutman for the defendant on the subject of latency in NIHL and the advancement on behalf of the claimant of a phenomenon which has previously been described as ‘hidden hearing loss’, that is, damage which cannot be seen on standard audiometric testing. 



The claimant alleged exposure to excessive noise during employment with the defendant as an Electrician between 1979 and 1992 at various large scale industrial sites including chemical plants and oil refineries in the North West.  The claimant alleged that he would regularly work 12 hours a day in constant noise.   He alleged exposure to noise from the operation of turbines, drill towers, presses, compressors and general heavy industry.  

The claimant had alleged similar exposure which 2 other employers between 1974 and 1979 and 1993 and 1998. The claims against these employers were compromised at an earlier stage of litigation.

The remaining defendant admitted breach of duty. An audiogram in 2011, obtained as part of Mr Zeitoun’s medical report, showed NIHL. The primary issue in dispute was causation which centred upon the discovery of an audiogram dated 28.10.1993,undertaken as part of a BUPA health screening, soon after the claimant’s employment with the defendant had ended.  The 1993 test showed no audiometric evidence of NIHL. 

As well as the audiogram from 1993, there was reference in the claimant’s medical records to a further hearing test undertaken by BUPA as part of an earlier screening in 1987.  Although no 1987 audiogram was located, the records relating to the 1987 test referred to the claimant having ‘normal hearing’.   

In view of the audiometric evidence from 1987 and 1993, the remaining defendant denied causation.


Expert Evidence

The claimant’s expert, Mr Hisham Zeitoun, Consultant Otolaryngologist Head & Neck Surgeon, had not referred to the BUPA health records or 1993 audiometry in his initial report and had relied solely upon an audiogram undertaken at the time of his examination of the claimant in February 2011 which was compliant with the ‘Coles guidelines’ for diagnosis of NIHL. 

When questioned by the defendant on the BUPA records, Mr Zeitoun initially agreed that ‘if the audiogram of 1993 is a true representation of Mr Ross’ hearing at the time, Mr Ross has not suffered noise induced hearing loss prior to that audiogram’.

Subsequently, Mr Zeitoun questioned the accuracy of the 1993 BUPA hearing test and opened the door for the claimant’s ensuing argument that even if the audiogram were accurate, the claimant had nevertheless sustained some damage to his hearing as a result of alleged exposure with the defendant notwithstanding the fact that it was not revealed on the 1993 audiometry.

The claimant was granted permission to reply upon further medical evidence from Professor Brian Moore, Emeritus Professor of Auditory Perception in the Department of Psychology at the University of Cambridge. 

Professor Moore’s evidence was summarised by the judge, HHJ Wood QC, as follows:


‘His evidence was that whilst the obvious effect of noise exposure would be damage to the outer hair cells within the cochlea where such damage was usually identifiable by the thresholds revealed on audiometry, it did not necessarily follow that hair cell damage would give rise to a noticeable loss when detecting sound.   He relied upon a number of animal studies to demonstrate that mild changes could be caused to the outer hair cells without any measureable change in the thresholds.  Because damage to the auditory system built up gradually, reflecting the cumulative energy received by the ears, there will be a time before the damage is evident’.


The defendant relied upon the medical opinion of Professor Mark Lutman, Professor of Audiology at the Institute of Sound and Vibration Research in Southampton.  Professor Lutman observed that the 1993 audiogram showed more or less normal hearing which led him to conclude that any NIHL which might have been present on the 2011 audiogram must have occurred after 1993 or alternatively any loss was due to idiopathic (unknown) causes. He saw no reason to doubt the accuracy of the 1993 audiogram. On the question of whether or not there could be latent effects of noise exposure, Professor Lutman referred to the received wisdom from expert and consensus groups that there were no such measureable latent effects.  

Put simply, if the loss had not occurred as a result of alleged exposure with the defendant (in light of the 1993 audiogram demonstrating normal thresholds), then the 2011 test could only be explained by subsequent exposure or it was idiopathic, insofar as sensorineural hearing loss of unknown origin was common in the general population and could mimic NIHL.

There was an agreement between Professor Moore and Professor Lutman regarding the theoretical scientific arguments on the hidden effects of noise exposure based on various animal studies but disagreement as to how they could be applied in the claimant’s case particularly as pointed out by Professor Lutman, in view of the physiological differences between species.  In the joint statement Professor Moore and Professor Lutman agreed:


“…there are theoretical arguments and limited data that there might be certain latent effects.   It is well established from animal studies that noise exposure may cause quite substantial damage to the hair cells in the inner ear without causing any hearing loss as gauged by the audiogram.   It has also been shown in recent animal studies (mice) that exposure to high levels of noise can damage the synapses between inner hair cells and neurons directly; it can lead to degeneration of neurons in the auditory nerve without measurable effects as gauged by the audiogram.  Such degeneration of neurons may continue for months or years after noise exposure has ceased’.


In summarising the issues to be determined, HHJ Wood identified that the first question for the Court was whether or not the 1993 audiogram was an accurate representation of the claimant’s hearing loss at that time.  


The accuracy of the 1993 audiogram

Mr Zeitoun gave evidence that he was concerned about the efficacy of the 1993 audiogram on the basis that it had been confirmed by BUPA that the test would not have been conducted in a soundproof booth. 

Professor Lutman took the view that the 1993 test was entirely plausible and stated that the usual concerns about testing conditions and in particular, ambient noise would serve to make thresholds worse than they actually were.   As the claimant’s 1993 audiogram showed some thresholds recorded down to zero, there was no evidence that ambient noise would have been a problem, and no evidence that the audiometry had been obtained other than in an entirely proper fashion.

Mr Zeitoun accepted under cross examination that ambient noise would make thresholds worse and not better but advance a number of factors he considered could make a recorded threshold better than was actually heard.   These included:

-          Visual signals from the operator who may be within sight of the subject;

-          An audible click from the testing machine if it had mechanical components;

-          The absence of irregular intervals between the sounds tested.


Such factors, Mr Zeitoun asserted could make the subject predict when a sound was being emitted which in turn would lead to a belief that he had heard the sound when he had not.

HHJ Wood QC found that there was no shifting the burden of proof and that it was not incumbent on the defendant to satisfy the court that the 1993 audiogram was accurate.  He stated:


‘The audiogram is included in a compendium of the medical records, the accuracy of which would normally be self-proving, in the absence of any significant contradictory material’.


He went on to say:


‘There is simply no evidence that the audiogram carried out by BUPA….did not properly measure hearing thresholds. By referring to audible clicks from the audiometry mechanism, visual signals, or the lack of variation in the spacing of the sound pulses, the claimant is indulging in speculation without real evidence’.


Additionally, he stated that the fact the claimant did not complain of hearing difficulties in 1993 was a further factor which undermined the claimant’s challenge to the efficacy of the 1993 test.   On the subject of Mr Zeitoun’s position he remarked:


‘Insofar as Mr Zeitoun has called the audiogram into question, he has lost objectivity because of his shifting position and has indulged in litigation bias, whereby his position became harder as the issues crystalized’.


Latency of damage

Having found that the 1993 audiogram was accurate, the second question for consideration was whether the claimant had established, on the balance of probabilities, that notwithstanding the absence of any hearing loss in 1993 at the end of his employment with the defendant, he had nevertheless sustained some damage to his hearing which became evident in later years and which was not related to the ordinary ageing process.  

HHJ QC declined to be drawn into making a decision which answers a generic question about occupational deafness litigation.  He stated:


‘This is especially so because on the face of it the question depends upon the non-expert interpretation of a complex medical/scientific debate which is ongoing based on a plethora of epidemiological studies in both humans and animals, and where there is yet to be any consensus’.  It is axiomatic that every case is fact specific and a decision has to be made upon the evidence presented, of which scientific research is but a small part’. 


In considering the argument advanced on behalf of the claimant by Professor Moore, HHJ Wood QC noted that Professor Moore had accepted that it was unusual that there was no recorded loss on the 1993 audiogram given the claimant’s alleged history of exposure and agreement by Professor Moore than in general, NIHL progresses more rapidly earlier on.  Professor Moore had speculated that the claimant may have had an usually large cochlear reserve however the Judge preferred the evidence of Professor Lutman that such was unlikely.

In finding for the defendant, HHJ Wood found that Professor Moore’s conclusions were fundamentally flawed because they were based on the assumption that the claimant was exposed to the same constant noise levels throughout his entire working history.  There was no engineering evidence in the case and the argument presented by Professor Moore would flounder if noise levels after 1993 were greater than those prior to this date.  

Notwithstanding the absence of compelling engineering evidence, the Judge held that the claimant would still have faced a difficulty because there was no evidence that underlying synaptic damage not revealed on threshold had actually taken place prior to 1993 in the claimant’s case.   The Judge found that in the absence of any reported difficulties prior to 1993, the court would be embarking on a highly speculative exercise were it to conclude that synaptic damage had been occurring, which meant that the claimant was more vulnerable to hair cell damage in later years.  

HHJ Wood concluded:


‘It seems to me that both Professor Lutman and Professor Moore have been engaged in an honest intellectual interpretation of the research literature and it is unnecessary for this court to determine which of the theories is preferred.    I conclude that whilst there was a possibility of latent damage occurring to the nerve structures in the cochlea not detectable on the 1993 audiogram, this falls significantly below being a probability in the light of all the evidence which has been made available to this court.    It is unnecessary to make any further determination, or to provide any generic ruling on the scientific question although it does appear unlikely that there will be any sufficient consensus on that question, or means by which such damage could be measured for some time to come’.


New LCB Guidelines on disability considered

In previous editions of BC Disease News (124 and 129) we have considered the new LCB Guidelines on assessment of NIHL & disability in NIHL claims.

The issue of the appropriate method for evaluating hearing disability was briefly considered by HHJ Wood who said:

The issue arises from a determination as to which of the centiles is appropriate to the Claimant. Professor Lutman has adopted a less than generous approach in the sense that he has followed newly published guidelines (to which he is a significant contributor) which are intended to incorporate ‘best fit’ by reference to certain anchor points. I accept his evidence that previous assessment guidelines (again to which he has contributed) provided a rough and ready approach taking an individual Claimant as averagely susceptible at the 50th centile.

It is correct in this respect that if one were to take 1 and 8 kHz the Claimant is far closer to the 25th percentile for ageing, and this would have the effect of reducing the measured thresholds at 1, 2 and 3 kHz. However, it is noteworthy that Mr Zeitoun, and indeed Mr Welsh who provided the initial report [for the defendant] had taken a more traditional line which appears to be founded on the Black Book guidance over 20 years ago, and there is some substance to Mr Zeitoun’s argument that the 2016 guidelines themselves provide scope for some flexible interpretation allowing individual variability. As I remarked in court, the issue as to whether or not the 4 kHz threshold should be taken into account remains a controversial one, because in some respects it has an effect on the disability. It remains to be seen whether or not those involved in medico-legal work adopt the potentially less generous interpretation without applying the exceptions which appear to emanate from the more recent guidelines.

However, this particular case I would have had some sympathy with the approach of Mr Zeitoun if it had been necessary to assess the disability, and to have compensated the Claimant on the basis of an approximate 10 decibel threshold hearing loss over 1,2 and 3 kHz, which was indeed the preferred approach of Mr Welsh.’


Comment and conclusion

The judgement supports the conventional view that NIHL occurs at the time of exposure and underlines the value of contemporaneous audiometry in determining issues of causation in NIHL claims.    The burden is on the claimant in every case to prove that he has sustained a compensable injury as a result of alleged exposure, on the balance of probabilities.  Where standard audiometric evidence does not support a finding on NIHL and the claimant does not report any contemporaneous hearing difficulties, a claimant is unlikely to discharge the burden on the basis of hypothetical scientific principles.

Some of the important issues raised in this case will be considered in further features of BC Disease News.