22
2.35 Risks deriving from exposure to
noise:
Noise characteristics and measurement
Noise is a pressure variation in an elastic medium,
generally the air, produced by the variation of a
material body (source) that determines an undesired
and often annoying acoustic sensation. Noise is
mainly characterized by;
Sound intensity or level: expresses the entity of
the pressure variation due to the sound wave.
Measured in decibels (dB), It doubles the sound
intensity and, thus, the energy that reaches the
ear.
Frequency: expresses the number of pressure
variations of the wave per second and is
measured in Hertz (Hz)- acute noises have high
frequencies (2000-4000 Hz or more) while low-
pitched noises have low frequencies (250 Hz or
less).
How the risk is evaluated: The higher the sound
level and exposure time, the greater the noise risk
will be:
LAeq: (Equivalent continues weighted level A):
this is a sound level measurement that takes into
account noise fluctuations and the varying
sensitivity of the ear to the frequencies: LAeq is
measured with a sound: level meter;
PEL (Personal Exposure Level): this is a
measurement that takes the various noise levels
into account along with the time the worker
remains on the individual machines or working at
determined processes: PEL is calculated
mathematically.
Noise pathologies
Damage to the hearing
Noise causes hyperdulia or deafness because it
destroys the acoustic receptors, nervous cells able to
transform the mechanical sound vibrations into
nervous impulses that, on reaching the brain,
determine the aural sensation. These receptors are
irreplaceable if they are destroyed and the resulting
damage is irreversible: hyperdulia worsens if
exposure to noise continues and does not improve
even if this terminates.
Moreover, it is also bilateral since it can be
accompanied by annoying buzzing and whistling
sounds, and by intolerance to loud noise.
The damage is insidious since it proceeds slowly and
unexpectedly: in the initial phase, when it is limited to a
diminished ability to perceive acute sounds (music,
bells) or the spoken voice when there is a background
noise, it can only be detected by means of an
!
!
!
!
!
(Fig. 2-32)
SAFETY NOTES
audiometric test. Pulsating noises of great intensity
lasting a very short time are highly damaging since the
ear is unable to actuate any physiological protective
measures in time. Hyperdulia from noise generally
arises after several years of exposure and depends on
the PEL (risk almost null below 80 dBA) and on
individual characteristics. It is an incurable disease:
the only efficacious means of protection against it is
prevention.
Other effects
Noise does not just determine aural sensation. For
levels exceeding* 70dBA, it causes stress by
means of the cerebral integration centers and
determines a specific neurovegitative reaction
responsible for effects that lead to cardio circulatory
and gastro enteric diseases. Amongst these, it is
worthwhile noting: an increase in gastric acidity, a
decrease in the heart rate, visual range and reflex
speed; a sensation of discomfort and weariness with
an increased sense of fatigue.
These effects are dangerous because they also
increase the risk of accidents.
Personal equipment to protect against noise
Individual protective equipment attenuates the sound
energy transmitted to the ear through the air. This
equipment is used when dangerous exposure cannot
be avoided in any other way.
There are different types of devices with different
attenuating capacities: helmets, ear muffs, ear plugs
(Fig.2-32). Helmets and ear muffs offer the greatest
protection but they are bulky and inconvenient to wear.
They are therefore only of use for exposure to high
noise levels but for short periods of time (max. 2
hours).
Ear plugs are generally tolerated to a greater extent
and are of particular use in the case of lengthy
exposure to noise of a lesser intensity.
Always use adequate individual protective equipment
to safeguard the hearing when the personal daily level
of exposure to noise is 85.5 dBA when tractor is
moving and 82dBA while tractor is stationary.
O P E R A T O R M A N U A L S O L I S 9 0 ( C R D I )
To Next Page
Loading...
