‘Sliding Scale’ Approach to Diagnosing NIHL – A ‘Novel Battleground’?

Under the ‘Guidelines on the diagnosis of noise-induced hearing loss for medicolegal purposes’, written by Coles, Lutman and Buffin (the CLB Guidelines) and published in 2000, the following 3 requirements must be satisfied to result in a diagnosis of noise-induced hearing loss (NIHL):

  • R1 – high-frequency hearing impairment;
  • R2 – potentially hazardous amount of noise exposure; and
  • R3 – identifiable high-frequency audiometric notch or bulge.

Typically, successful claimants will prove a cumulative noise immission level (NIL) above 100 dB(A) [requirement R2(a)] and an audiometric bulge/notch, exceeding 10 dB [requirement R3(a)].

However, at paragraph 6.1 of the Guidelines, the authors acknowledge that:

‘Substantial amounts of NIHL can be caused in a minority of persons exposed to < 100 dB(A) NIL; that is, in those who are more than averagely susceptible’.

As such, claimants are also permitted to prove a lower NIL in the range of 90-99 dB(A) [requirement R2(b)], alongside a higher audiometric bulge/notch, exceeding 20 dB [requirement R3(b)].

At present, the 2 mechanisms through which NIHL can be identified [i.e. R1 + R2(a) + R3(a) OR R1 + R2(b) + R3(b)] makes for diagnostic criteria that could be adequately described as binary. Testament to this is the fact that a person exposed to 99 dB(A) NIL still has to demonstrate high-frequency notching or bulging of at least 20 dB, even though their lifetime exposure is much closer to 100 dB(A) [the R2(a) threshold] than 90 dB(A) [the R2(b) threshold].

In July, Christopher Lowe, of Ropewalk Chambers, issued an article focusing on the emergence of ‘novel battle grounds’ in an ‘ever-decreasing pool of viable NIHL claims’.[i]

In particular, he observed that claimants are increasingly applying a so-called ‘sliding-scale’ approach to R2 and R3, thus challenging the orthodoxy of R1 + R2(a) + R3(a) AND R1 + R2(b) + R3(b) when proving medical causation.


Although one could argue that there is some mathematical logic in this approach, to accept it would be to undermine the rationale for having 2 distinct methods of fulfilling conditions R2 and R3.

To date, Mr. Lowe confesses that he has not been present at a trial where the Court has found in the claimant’s favour on this issue. That being said, he warns that defendants ‘must be alive to the issue at an early stage in any case in which the argument is likely to be raised’.

Various fronts on which judges have rejected the ‘sliding scale’ include:

  • Strict adherence to mandatory language used in paragraph 6.1 of the Guidelines, leaving no room for interpretation.
    • Where the estimated total exposure is in the range of 90 to 99 dB(A) NIL, thereby meeting noise exposure guideline R2(b) but not R2(a), the audiometric guideline must be met instead of R3(a).
  • Recognition that the dataset underpinning the Guidelines (200 medico-legal cases) has not undergone ‘proper statistical analysis’, rendering any suggested alternative approach mere ‘speculation’.
  • Reference to paragraph 7.4 of the Guidelines.
    • It is expressly acknowledged that ‘the absence of a notch or bulge of sufficient size to meet R3(a) or (b) does not preclude the presence of some NIHL hidden in hearing impairments having other causation, or of NIHL having an atypical audiometric configuration. But such possibilities would generally be below the balance of probabilities.
    • The express exception to R3(a) and R3(b), namely ‘where the size of the notch or bulge only just fails to meet the guideline, but the noise exposure had been particularly high (over 110 dB(A) NIL, for example)makes it unlikely that an implied ‘sliding scale’ approach is also viable.
  • Lutman, Coles and Buffin’s ‘Guidelines for quantification of noise-induced hearing loss in a medicolegal context’ (LCB Guidelines) – the sequel to the original Guidelines, published in 2016 – made no changes to the formulae for diagnosing NIHL.
  • The absence of any peer-reviewed paper considering the merits of a ‘sliding scale’.

For now then, the ‘sliding scale’ approach is nothing more than a ‘superficially attractive’ idea. More now than ever before, defendants should be incentivised to obtain their own medical evidence and ask appropriate Part 35 questions of opposing experts, in order to prevent ‘novel battle grounds’ from becoming established ones.


[i] Christopher Lowe, ‘Noise-Induced Hearing Loss and Medical Causation: NIL on the Slide!’ (28 July 2021 Ropewalk Chambers) <https://www.ropewalk.co.uk/knowledge-sharing/blog/disease/1837/noise-induced-hearing-loss-and-medical-causation-nil-on-the-slide> accessed 13 August 2021.