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Exposure to noise

Noise is usually defined as unwanted sound. Noise exposure may result in different effects on exposed persons depending on the noise level. Low level noise mainly induces speech interference or annoyance. At higher  noise levels these effects increase, and in addition physiological effects may appear as well as effects on hearing in terms of hearing loss and/or tinnitus.

An octave band sound pressure level below 65-70 dB is not considered to cause any temporary threshold shift, regardless of frequency or duration of the noise. Above the minimum exposure level for temporary threshold shift and up to 120 dB SPL, temporary threshold shift increases almost linearly with duration and level. Standardised risk criteria for noise-induced hearing loss are presented in ISO 1999 (International Organization for Standardization, 1990). The risk criteria are based on sound pressure levels measured with A-weighting, to resemble the damage risk to the inner ear.

The level of the noise that might induce hearing loss depends on the duration of the exposure. Based on a dose-effect assumption the critical level for noise-induced hearing loss is set to 85 dB(A) during 8 hours per day. However, the individual variation in susceptibility is large and even for this dose some subjects are likely to be affected. According to the equal-energy principle an increase by 3 dB would halve the permissible duration. This implies maximum 28 seconds noise exposure at 115 dB(A). For short lasting impulse sounds the peak level, regardless of the total energy, might cause a permanent threshold shift.




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Magnus Johansson, Peltor AB







 THE AUDITORY SYSTEM

  How does sound occur
  The auditory system 
  The outer ear 
  The middle ear
  The inner ear
  Hearing
  Exposure to noise 
  Hearing impairment
  The concept of equal energy
  How to measure noise levels
  Choose right hearing protection
  Do not over attenuate
  Noise regulations