Noise-Induced Hearing Loss and Medical Causation: NIL on the Slide!

In this blog, Chris Lowe reviews the current requirements for proving medical causation in NIHL claims, reviewing recent practice in relation to the “Guidelines…” paper and considering the “R3” requirement

With an ever-decreasing pool of viable NIHL claims, novel battle grounds inevitably develop. One such battle ground is the so-called ‘sliding-scale’ approach to the requirements of R2 and R3, with a view to establishing medical causation by reference to the well known “Guidelines…” paper of Coles, Lutman & Buffin, published in 2000 (“CLB”).

Those who routinely litigate NIHL claims will be only too familiar with the orthodox application of the CLB Guidelines, further to which three main requirements must be satisfied, namely:

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

For the purposes of R2(a) and R2(b), paragraph 6.1 of the CLB Guidelines provides that: if the audiometric bulge/notch exceeds 10 dB, the Claimant must prove a cumulative noise immission level (“NIL”) of more than 100 dB(A) NIL: R2(a). By contrast, if the audiometric bulge/notch exceeds 20 dB, the cumulative NIL requirement is reduced to 90 dB(A) NIL: R2(b).

The rationale underpinning the diagnostic requirements is explained in paragraph 6.1 of the CLB Guidelines. The authors acknowledge that substantial amounts of NIHL can be caused in a minority of persons exposed to less than 100 dB(A) NIL; that is, in those who are more than averagely susceptible to the effects of noise exposure.

To allow for such cases, the less stringent diagnostic requirements of R2(b) and R3(b) were therefore formulated. Accordingly, where the estimated total exposure is in the range 90-99 dB(A) NIL, thereby meeting noise exposure guideline R2(b), but not R2(a), the audiometric guideline R3(b) must be satisfied instead of R3(a).

Increasingly, Claimants seek to apply a ‘sliding scale’ approach to the requirements of R2 and R3 in circumstances whereby the available audiometry reveals notching/bulging of between 10dB and 20db where there is an estimated NIL of less than 100 dB(A).

The so-called sliding-scale argument is advanced as follows: if the NIL exceeds 90 dB(A) but does not exceed 100 dB(A), an audiometric notch/bulge between 10 dB and 20 dB ought to be sufficient to establish NIHL. For example, if the audiometric notch/bulge is 15 dB (being a mid-point notch/bulge between R3(a) and R3(b)) then (so it is argued) causation ought to be established by with evidence of a cumulative NIL of 95 dB(A)NIL, being the midpoint NIL between 90 dB(A) and 100 dB(A) as identified by R2(a) and R2(b).

Whilst superficially attractive, not least due to its apparently simple ‘logic,’ the argument has not so far, in the cases in which I have appeared at trial, found favour. In the main, the Court has rejected the argument for various reasons, the instances of which follow:

1. It is contrary to paragraph of 6.1 of the CLB guidelines, which expressly provides: ‘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).’
2. The approach fails to have due regard to the data set underpinning the CLB guidelines (some 200 medico-legal cases). In the absence of proper statistical analysis of the underlying data set, the contended for interpolation of audiometric notching/bulging against a notional NIL sliding scale is no more than speculation.
3. The CLB guidelines were formulated with a view to distinguishing between a ‘probable’ and ‘possible’ diagnosis of NIHL (including in borderline cases), whereby the authors of the expressly acknowledge that whilst the absence of a 10 dB or a 20 dB notch/bulge (for the purposes of R3(a) and R3(b) respectively), does not preclude the presence of NIHL, such audiometry would generally not permit a diagnosis of NIHL on the balance of probabilities.
4. Paragraph 7.4 of the CLB Guidelines expressly provides for an exception to the strict requirements of R2(a) or R2(b), whereby diagnosis may be permitted if the audiometric notch or bulge only just fails to qualify for the purposes of R3(a) or R3(b), but noise exposure has been particularly high, NIL over 110 dB(A) for example. Such a state of affairs militates against the viability of the contended for sliding scale approach, especially in the context of a NIL in the range of 90 to 99 dB(A).
5. The authors of the CLB Guidelines conducted a review of the Guidelines in 2016 (Lutman, Coles & Buffin 2016) but did not consider it appropriate to amend the diagnostic criteria formulated for the purposes of R2(a) and R2(b) or R3(a) and R3(b). Likewise, the merits of the contended for sliding scale approach have not been the subject of any peer-reviewed paper. Again, such a state of affairs militates against the viability of the contended for sliding scale approach.

Only time will tell if this novel battleground continues to develop. What is clear, is that Defendants must be alive to the issue at an early stage in any case in which the argument is likely to be raised. The obtaining of alternative medico-legal opinion to that relied on by the Claimant must always be considered. Likewise, appropriately framed Part 35 questions can assist to narrow issues well in advance of trial. As always, forewarned is forearmed!