There are many different types of noise associated with the workplace. In general terms, they can result in two forms of hearing loss:
- noise induced hearing loss; and
- acoustic trauma.
Noise induced or sensori-neural hearing loss
This form of hearing loss is produced gradually from long term exposure to noise. Over its years of development, the condition begins by affecting high frequencies (usually at the 4000 Hz level) and eventually those at the lower levels.
Employees suffering from industrial deafness will have reasonably normal low frequency hearing, but distorted high frequency hearing. The volume of speech is unaffected, yet the clarity of speech, determined by consonants, lessens.
The degree of binaural hearing loss tends to be linearly proportional to the duration of exposure to workplace noise.
When there is a single incident involved and it results in trauma to the acoustic organ, it is known as acoustic trauma.
Example
A RAAF member accidentally discharges his firearm in a vehicle, prior to dispersing birds from the runway. The member may suffer the effects of acoustic trauma.
An audiogram of a person suffering from acoustic trauma may show a flat loss, a high frequency loss or a low frequency loss.
Where loss of hearing is attributable to a single traumatic event, the special policy rules which allow a 1988 hearing claim to be treated under the 1971 Act would not apply as the hearing loss became permanent at the time of the event and was not caused over a period of time.
Deterioration of noise-induced hearing loss not compensable after discharge
Specialist medical advice indicates that noise-induced (sensori-neural) hearing loss will not continue to deteriorate once exposure to workplace noise has ceased. Accordingly, any deterioration in hearing after the date of discharge cannot be attributed to Defence employment and must arise from other factors such as the ageing process or further exposure to noise in civilian life. Note however that, in appropriate circumstances, deterioration in other forms of hearing loss (eg. conductive deafness) may continue to be related to Defence employment after discharge.
Assessors should bear this specialist medical advice in mind when advising discharging or discharged members about any possible future entitlement to compensation for the permanent impairment of loss of hearing.
Assessors should also note that there will be the occasional case where the “date first sought medical treatment” (ie. the Date of Injury) was after the member left ADF employment. In such cases, where the date of injury is after the commencement of new hearing loss provisions on 1 October 2001 (or exposure to noise continues after that date), a 2.5% WPI threshold applies (the previous threshold was 10% WPI). In such cases, the assessor must be satisfied that the assessed hearing loss is due to noise exposure during military service and not exposure subsequent to discharge from the military.