Occupational noise induced hearing loss develops over a long period as a result of exposure to continuous or intermittent loud noise. Occupational acoustic trauma is a sudden change in the hearing caused by a single exposure to a sudden burst of very loud noise such an explosion.
The main features of noise induced hearing loss are:
1. It is sensorineural affecting the hair cells in the inner ear
2. It is almost always bilateral and the audiometric patterns are usually similar bilaterally. An exception would be the exposure of a soldier to the noise of his rifle.
3. Once the noise exposure has ceased there will be no further progression of hearing loss as a result of noise exposure. The overall hearing loss will however be increased by other conditions, most commonly presbyacusis (age deafness).
4. The awareness of hearing loss is gradual and it may be many years after the exposure before it is noticed by the sufferer.
5. The earliest damage in the inner ears reflects a loss at 3000, 4000 and 6000 Hz. The greatest loss will occur at 4000 Hz, accordingly the notch on the typical audiogram of a person suffering from noise induced hearing loss will be apparent at that frequency.
6. Continuous noise exposure over the years is more damaging than intermittent exposure to noise.
The Symptoms of Noise Induced Hearing Loss
1. Speech can be heard but the words are not clear
2. Difficulty distinguishing certain sounds like "f", "s" and "t" sounds
3. Some sounds may appear distorted.
4. The sufferer speak very loudly.
5. Difficulty hearing where there is background noise, such as in the pub.
6. The sufferer will tend to have the television turned up very loud.
Tinnitus
This is a condition which can also be caused by exposure to excessive noise. The sufferer hears noises in one or both ears, which can be intermittent or constant. The noise is often so intrusive that it can affect the sufferer's concentration or prevent them from getting to sleep. This in turn can lead to depression. It is generally accepted that where noise induced hearing loss and tinnitus are both present they are the result of the same noise exposure.
The Sources of Industrial Noise
The most common employments where excessive noise is experienced are heavy productive industries such as engineering, textiles, shipbuilding, printing, mining and quarrying. The sources of noise are tools, vehicles, heavy plant and machinery.
The Measurement of Noise
Noise is measured in Hertz (Hz). Sound intensity is measured in decibels (dB).
0 is the faintest sound audible to the human ear. The noise from a jet engine is around 120 - 140 dB.
It is generally accepted that exposure to noise levels of more than 90 dB are likely to cause damage to the hearing and that the short periods of exposure to very high levels of noise will also cause damage.
It is also acknowledged that exposure to noise levels in excess of 85 dB is also harmful.
Date of Knowledge
Medical awareness of occupational deafness has existed for over 150 years. The Ministry of Labour's 1963 publication, Noise and the Worker, marks the watershed and from that date industrial employers would have been expected to know that exposure to noise levels of 90 dB or more for 8 hours a day could damage the hearing.
Contact Hilary Meredith Solicitors
Author Resource:
Written for Hilary Meredith Solicitors by Olwyn Kinsey author of Noise Induced Hearing Loss related literature.
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