6.2 Effects of noise on the individual

Question 1

For sound to travel through the ear, four different types of energy are required:

Answer 1

 Acoustical energy or sound waves set the tympanic membrane into vibration
synchronous to the sound pressure compression and rarefaction cycles.
 Mechanical energy as the vibration is transmitted by the movement of the
eardrum and the ossicular chain.
 A travelling wave, through the scala tympani as the oval window is pushed in, by
the piston-like motion of the stapes footplate.
 Biochemical energy that sends an electrical signal along the cochlear nerve to
the auditory cortex for interpretation as sound.

Question 2

Health effects of noise

Hearing loss may be

Answer 2

conductive, sensorineural, or mixed

Question 3

Conductive hearing loss

Answer 3

Conductive hearing loss occurs when the sound pathway is blocked in the outer
and/or middle ear, reducing the vibration that reaches the inner ear. Conductive
hearing loss is diagnosed when bone conduction hearing thresholds are better than
air conduction thresholds.

Question 4

Sensorineural hearing loss

Answer 4

Sensory hearing loss is specific to the cochlea and neural hearing loss is due to
pathology within the auditory nerve and/or central auditory pathway. The term
sensorineural hearing loss is used to cover both a specific diagnosis is difficult
without sophisticated diagnostic equipment.

Sensorineural hearing loss is less likely to be medically treatable and more likely to
be permanent than conductive hearing loss. Sensorineural hearing loss can be
caused by medications or environmental exposure to certain chemicals. More
relevant examples of sensorineural hearing loss are:
 Prebyacusis – or age-related hearing loss (ARHL)
 Noise-induced hearing loss (NIHL).

Question 5

A temporary threshold shift (TTS) is

Answer 5

a hearing loss which shows some recovery
within 24-48 hours after the noise exposure stops. The more intense (louder/longer)
the exposure, the longer the expected recovery period would be.

Question 6

permanent 
threshold shift (PTS)

Answer 6

Hearing loss which
persists more than 30 days after the noise exposure is considered to be permanent
threshold shift (PTS) and recovery is unlikely.

Question 7

Where the health surveillance identifies hearing damage the employer shall ensure
that the employee is examined by a doctor. If the doctor considers that the damage
is likely to be the result of exposure to noise, the employer shall:

Answer 7

a) ensure that a suitably qualified person informs the employee
b) review the risk assessment
c) review control measures
d) consider assigning the employee to alternative work where there is no risk from
further noise exposure
e) ensure continued health surveillance and a health for any other employee who
has been similarly exposed.

Question 8

Interpreting the audiogram

Answer 8

 Frequency (Hz) is plotted from low to high pitch along the x axis (horizontal).
 Intensity (dB HL) is plotted from soft to loud along the y axis (vertical).
 Air conducting thresholds are indicated by an ‘X’ for the left ear and an ‘O’ for the
right ear.
 Noise induced hearing loss typically presents with a classic ‘notch’ at around
4kHz.