Hearing Impairment

  Noise Induced Hearing Loss (NIHL) - Hearing loss can result from exposure to even relatively short duration noise. The degree of impairment is influenced mainly by the intensity of the noise. Such damage is known as Noise Induced Hearing Loss (NIHL).

  Hearing loss can be temporary - lasting from a few seconds to a few days - or permanent. 
  Temporary hearing loss may be caused by relatively short exposure to very loud sound, as the hair-like cells on the basilar membrane take time to ‘recover’.
With additional exposure, the amount or recovery gradually decreases and hearing loss becomes permanent. Thus, regular exposure to high levels of noise over a long period may permanently damage the hairlike cells in the cochlea, leading to irreversible hearing impairment.

Three levels of noise at which an employer must act:
     a) 85 decibels (if normal speech cannot be heard clearly at 2 metres), employer must;
         • assess the risk to employees’ hearing,
         • tell the employees about the risks and what precautions are proposed,
         • provide their employees with personal ear protectors and explain their use.
    b) 90 decibels (if normal speech cannot be heard clearly at 1 metre) employer must;
        • do all that is possible to reduce exposure to the noise by means other than
          by providing hearing protection,
        • mark zones where noise reaches the second level and provide recognised
          signs to restrict entry.
    c) 140 decibels (noise causes pain).
 Noise Dose - combination of duration and intensity of noise can be described as noise dose. Exposure to any sound over 80 dB constitutes a noise dose, and can be measured
over the day as an 8 hour Time Weighted Average sound level (TWA).

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