|
  Exposure of
workers to noise represents one of the most diffused risks of the modern
industrialized world. Its importance varies depending on the productive
typology, the ward and the duties. In the occupational environment the
auditory effects of noise are of different types and are basically
represented by noise-induced hypoacusia, a pathology determined by
exposure to high noise intensity.
Occupational noise-induced hypoacusia is certainly the illness most
frequently compensated by the insurance institution. The problem of noise
in the hospital environment is twofold. On the one hand there is a
limited number of workers (such as workers of mechanical laboratories and
carpenter's shops , maintenance workers, technical systems workers and
laundry workers) exposed to specific noise risk. In fact, their working
conditions entail the possibility for the polluting agent to be present
even at very high levels. Such workers must be subject to sanitary
surveillance according to the law 277/91.
On the other hand another aspect must be considered: sound emissions can
disturb the peace and tranquillity especially needed by high risk
patients.
DEFINITIONS
sound: a change in air pressure that determines a regular and
periodical acoustic wave able to produce an auditory sensation.
noise: generally held separate from sound because generated by
irregular and non periodical acoustic waves that are psychologically
perceived as unpleasant and troublesome sensations.
NOISE CHARACTERISTICS
Noise is characterized by three elements:BR> frequency: it
depends on the number of cycles or periods (Hertz) that follow one
another in one second. The human ear perceives frequencies ranging from
16 Hz (low sounds) to 20000 Hz (high sounds).
intensity: it is the amount of energy carried by the acoustic wave
for unit of surface. The acoustic waves' intensity is measured in decibel
(dB). The decibel takes into account the level of variation of acoustic
pressure in relation to the auditory capacity of the human ear (dB 0 =
the lowest hearable level at 1000 Hz; dB 135 = pain threshold). The
decibel scale is logarithmical, in fact variations of +3dB double and of
-3dB halve the sound intensity.
timbre: is the quality of sound, in fact two sounds with similar
frequency and intensity can differ from each other. The sound timbre
depends on the shape of the sound vibrations.
NOISE MEASUREMENT
The phonometre is the simplest instrument to measure noise.
The weighting or weighing circuit A of the phonometre behaves, at the
different frequencies that it is made up of, like the human ear; it
underestimates the lower frequencies and overestimates the higher ones,
therefore, generally, noise measurement is expressed in dBA.
The phonometre generally measures the continuous equivalent level, that
can be defined as the dBA value of a continuous noise taking into account
all variations of sound level in time by comparing them to one single
continuous level of even energy (a sort of average value of noisiness).
The continuous equivalent level multiplied by the exposure time measures
the worker's level of exposure.
Il rumore è ritenuto lesivo per
l'udito sopra gli 85 dBALeq.
Sotto gli 80 dBALeq sono possibili effetti extrauditivi se esiste una
suscettibilità individuale, oppure se vi sono condizioni di lavoro o di esposizione
particolari.
Effetti uditivi del rumore
1) Spostamento temporaneo della soglia uditiva
Un suono o un rumore particolarmente intenso sono in grado di provocare
un innalzamento della soglia uditiva rispetto a quella di riposo, seguito
da un recupero della percezione uditiva che inizia al cessare
dell'esposizione e si completa in circa 16 ore.
Noise
is considered to damage hearing beyond 85 dBA continuous equivalent
level.
Below 80 dBA continuous equivalent level it is possible to observe extra-auditory
effects if there is individual susceptibility or in the case of
occupational or particular exposure conditions.
Auditory effects of noise
1) Temporary shift of the auditory threshold
A particularly intense sound or noise can provoke an elevation of the
auditory threshold if compared to the rest threshold. This is followed by
the recovery of the auditory perception that starts at the end of the
exposure and is completed within 16 hours.
2) Hypoacusia following chronic acoustic trauma or noise-induced
hypoacusia
After a few days of a new noisy job, especially at the end of the working
day the worker may complain of buzzing with sensation of full ears, light
headache and feeling of being in a daze. Afterwards these symptoms tend
to disappear so that the exposed worker has the impression of getting
used to noise. Once the endurance of the hearing apparatus is worn out, a
progressive worsening of the auditory threshold can be observed. The
worker cannot hear the watch ticking and the phone ringing any longer
(deficit for high frequency sounds).
Later the worker finds it difficult to hear his relatives' and
colleagues' voices and asks them to speak up; he feels the need to turn
up the volume of the radio and of the television to understand the words
(deficit for low frequency sounds). The auditory deficit at this stage is
irreversible and, in the majority of cases, does not evolve if the
exposure ceases. If the exposure continues and the worker does not employ
personal protective devices, the deficit will evolve and reach deafness
within years.
3)Hypoacusia following acuto acoustic trauma
This follows short exposure to a sound front of high intensity. It is
frequently unilateral because the head shields the heterolateral ear. The
tympanic membrane may break and the lesions can involve both the media
and the inner ear.
Extra-auditory effects
The main extra-auditory effects of noise that have been pointed out in
epidemiological studies involve:
- the cardiovascular system, with an increased incidence of hypertension,
ECG and heart rate changes up to myocardial infarction;
- the gastroenteric system with an increased number of aspecific problems
and of duodenal ulcer;
- the neuropsychical effects including the lengthening of the reaction
time, an increased number of errors during the carrying out of the job
and the interference of noise with the perception of possible danger
warnings. All these factors must not be underestimated because they can
lead to an increased risk of accidents.
For additional information
|
![[collegamenti]](ico/collEfdr.gif){kind=small}
