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

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. This was an observational, retrospective, repeated cross-sectional study. De-identified audiometric records of 64196 employees entering NSW coal mining in three representative five-year periods between 1991–2015 were utilised. 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. 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. [ABSTRACT FROM AUTHOR]