What is noise-induced hearing loss?
Noise induced hearing loss (NIHL) is a permanent hearing impairment resulting from prolonged exposure to high levels of noise. Occupational NIHL develops slowly over a long period of time (several years) as the result of exposure to continuous or intermittent loud noise.
The cumulative effects of excessive noise exposure can be observed as significant hearing loss from about 40 years of age.
Excessive sound at a frequency around 4,000 Hz initially damages the hair cells and the blood supply in the cochlea. The threshold shift is temporary at first but becomes permanent with higher sound exposures.
NIHL causes difficulties with speech perception, particularly at higher frequencies. Audiological testing shows NIHL is usually associated with a notch-shaped high-frequency hearing loss that is worst at 4,000 Hz, but often occurs between 3,000 and 6,000 Hz.
The national standard for exposure to noise in the occupational environment is an average daily exposure level of 85 decibels (dB). This is consistent with overwhelming scientific evidence indicating that exposure levels above 85 dB represent an unacceptable risk to the hearing of exposed people.
The decibel scale is logarithmic, so a 3 dB increase in the sound level represents a doubling of the noise intensity.
In many countries, excessive noise is the biggest compensable occupational hazard.
Hearing loss is measured by audiometric testing, which determines the threshold shift in decibels at various frequencies.
How can noise exposure be managed?
The Mines Safety and Inspection Regulations 1995 contain comprehensive noise control regulations governing the management of occupational noise in mining operations.
Refer to Part 7, Division 1 of the Mines Safety and Inspection Regulations 1995 for details of noise control requirements.
One of the key factors in managing and reducing workplace noise is the need for employers to have a noise report. This must be prepared as soon as practicable, but not later than 12 months from the commencement of mining operations. Once a noise report has been prepared, no further noise reports are required if introduced control measures:
- have proved effective in maintaining noise at or below the action level
- are continuously monitored for effectiveness.
If there is likely to be an increase in noise of 5 dB or more, another noise report will be required. Additional noise reports may be requested by a mines inspector if warranted by the noise climate in or around a mine.
The report is used to formulate a noise policy, and develop and implement a noise control plan. Elements of a noise control plan include engineering and administrative noise control measures, and the expected reduction in noise and exposure levels.
Workers need to be provided with information on risks to hearing associated with exposure to excessive noise, and supplied with hearing protective devices such as earmuffs and earplugs to protect against noise above the action level.
Workers also have responsibilities to help protect their hearing.
Away from work, high levels of leisure noise can come from more traditional activities such as motor bike riding, shooting, use of power tools, or from more contemporary sources such as pub bands, concerts and portable music players (with headphones or earbuds).
Just as with workplace noise, if you have trouble conversing over the noise level then it is potentially too loud and you need to reduce your exposure (e.g. turn the source down, move away from the source, wear suitable hearing protection).