Hearing threshold levels of Australian coal mine workers: a retrospective cross-sectional study of 64196 audiograms

Objective This study examined the hearing threshold levels (HTL) of workers commencing employment in Australian coal mines in the State of New South Wales (NSW). The aim was to establish if some degree of hearing loss was identifiable in the mandatory pre-employment audiograms of workers. Design This was an observational, retrospective, repeated cross-sectional study. Study sample De-identified audiometric records of 64196 employees entering NSW coal mining in three representative five-year periods between 1991-2015 were utilised. Results Although HTLs were lower (better) in more recent years, the results showed clinically significant hearing loss (>= 25dBHL) for older workers, 45-60 years. Pure tone average (PTA) hearing losses were greater at the higher frequencies associated with excessive noise exposure (3-6 kHz), than at the speech frequencies (0.5-4 kHz). Hearing loss in the left ears were higher compared to the right ears, with higher prevalence of audiometric notches in males. Conclusion Almost a fifth (14.8-20.1%) of male workers commencing work in NSW coal mines presented with an audiometric notch at 4 kHz. Further research is required to determine if these notches represent true NIHL, and how the residual hearing of workers may be conserved.

Automated summary

Although the hearing threshold levels were lower in more recent years, this study showed that older workers (45-60 years) in Australian coal mines in New South Wales had clinically significant hearing loss. There was a higher prevalence of audiometric notches in male workers, with a notable proportion presenting with an audiometric notch at 4 kHz. Further research is needed to determine the nature of these notches and how to conserve the residual hearing of workers.