Introduction to Health and Safety at Work

Ill-health effects of noise
Noise can lead to ear damage on a temporary (acute) or 
permanent (chronic) basis.
There are three principal 
acute
effects:
➤
temporary threshold shift – caused by short exces-
sive noise exposures and affects the cochlea by 
reducing the fl ow of nerve impulses to the brain. The 
result is a slight deafness, which is reversible when 
the noise is removed
➤
tinnitus – is a ringing in the ears caused by an intense 
and sustained high noise level. It is caused by the 
over-stimulation of the hair cells. The ringing sensa-
tion continues for up to 24 hours after the noise has 
ceased
➤
acute acoustic trauma – caused by a very loud noise 
such as an explosion. It affects either the eardrum or 
the bones in the middle ear and is usually reversible. 
Severe explosive sounds can permanently damage 
the eardrum.
Occupational noise can also lead to one of the following 
three 
chronic
hearing effects:
➤
noise-induced hearing loss – results from permanent 
damage to the cochlea hair cells. It affects the ability 
(b)
(a)
Tympanic
membrane
Chain of
ossicles
Oval
window
Round
window
Scala
vestibuli
Scala
tympani
Basilar
membrane
and spiral
organ
Cochlear
duct
Auditory
tube
Sound waves
in air
Mechanical
movement
of ossicles
Perilymph
Fluid
wave
Endolymph
Fluid wave
stimulates
basilar
membrane
and spiral
organ
Fluid
wave
Tympanic membrane
Oval window
Round window
Outer ear
Middle ear
Inner ear
Perilymph
Hammer Anvil Stirrup
Figure 15.7
Passage of sound waves. (a) The ear with 
cochlea uncoiled; (b) summary of transmission.

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