Noise in the Danish work
environment
Noise is very common in the Danish work environment. In NIOH’s Danish Work
Environment Cohort Study (DWECS), 29% report being exposed to noise so high
that they must raise their voice in order to be able to talk with
colleagues. In many industrial trades more than half of the respondents
answer that they must raise their voice and the percentage is even higher
among school teachers and day care workers. The mentioned percentages have
increased from 1990, which was the first time the study was conducted, till
today.
Noise-related hearing impairment
Noise-related hearing impairment is caused by sound waves that affect the
auditory organ directly, and it occurs at exposure to noise corresponding
to an average of 80 dB (A) over an eight-hour working day. It is very
difficult subjectively to assess the noise level in one’s own work
environment. If a person enters a room in which the sound level is 80dB
then the noise will not seem so high after a short while. If a person is
exposed to noise that varies then the person will not get used to the sound
level as periods with a high noise level will be perceived as too high.
Noise in the work environment may cause cardiovascular
diseases
Noise in the work environment may cause cardiovascular diseases. This
association has been subjected to many studies. However, the quality of
these studies is often very poor. That makes it difficult to document the
association between exposure to noise and health effects. On basis of
scientific studies much literature concludes that the limit for developing
cardiovascular diseases lies around 85 dB(A) if the average exposure is
eight hours per working day.
Noise can affect a foetus
Low-frequency sound waves can penetrate tissue and fluids and affect the
auditory sense of the foetus which develops during the last half of the
pregnancy. Tests on animals have shown that exposure to high sounds may
cause hearing impairment in the child. This is partly supported by studies
among pregnant women. Other studies also indicate that high noise at the
work place may lead to low birth weight.
Tinnitus
Tinnitus, a ringing sound in the ears, is a malfunction in the auditory
sense which makes it possible to perceive sounds without stimulation from
external sound sources. Most people have suffered from momentary tinnitus,
e.g. after a concert with high music. The development of tinnitus is very
complex, and there is no simple connection between developing tinnitus and
exposure to noise. Researchers agree that tinnitus is associated with
increased activity in the nerve paths from the ear to the brain, and that
this activity is wrongly perceived as sound. The most predominant
hypothesis ascribe loss of external hair cells great importance. Tinnitus
is often the first symptom of hearing impairment registered after many
years of exposure to noise, and tinnitus is probably the worst discomfort
in relation to hearing impairment. Tinnitus is often illicited by emotional
strain, e.g. disease or a death in the family, own disease etc. At worst
severe tinnitus can cause insomnia, concentration difficulties, bad temper
and depression.
Acoustic-related Vibroacoustic Disease
Long-lasting exposure to low-frequency noise can cause Vibroacoustic
Disease (VAD). The symptoms that occur after one to two years of exposure
can be gastrointestinal diseases, pharynx infections, bronchitis, and
change of mood. Longer exposure (five to nine years) can cause breast and
back pain, fatigue, infections, gastritis, symptoms from the urinary organs
and allergy. After more than ten years of exposure the symptoms can be
metal disease, bleedings from the nose and intestinal tract, varicose
veins, ulcer, colitis, arthralgia and musclar pain, and neurological
disturbances.
Other effects of noise in the work environment
The character of the noise also affects a person’s performance. Tests
indicate that several mental processes are affected negatively by noise,
e.g. non-relevant talk is the most common noise problem at many workplaces.
This effect is especially associated with whether it is possible to
perceive the content of what the colleagues say. Recent studies show that
it is the acoustic variation of the noise more than the content of what is
said that is important. Work tasks requiring that a person remembers much
information is especially sensitive to noise with high acoustic variation.
That may be a problem for people working in open-plan offices and for whom
it is not possible to close a door or find more quiet surroundings.
Noise affects some employees more than other
Some employees are more sensitive to noise in the work environment than
other, especially employees with hearing impairment who often use much
energy on following a conversation. The same applies for new employees who
receive training, employees who work under stressing conditions, who have
an increased risk of hypertension or pregnant women.
Health effects of noise in relation to the legislation
There is no or only little margin between the action value of the Danish
Work Environment Authority – the value is 80 dB(A) – and the strain level
for developing health effects. This small difference can be a problem as
some people have “ears of stone” and other people have “ears of glass”. The
standards for worker protection are based on the working population in
general, and the borderline value is close to the strain level for health
effects. It is therefore a question if the legislation protects the
especially sensitive groups.
Need for research
Much literature on the health effects of noise in the work environment is
not of sufficient quality. If one has high quality requirements when
selecting studies for evaluation of noise as the cause of cardiovascular
diseases then the association becomes more evident than if all existing
studies are included in the evaluation. If there actually is a risk of
developing health problems when exposed to noise then the studies of high
quality will increase the probability of proving the associations in the
studies. Future research ought to be multidisciplinary as noise-related
problems occur in combinations with other psychosocial exposures at the
workplace. Hearing impairment is the most severe effect of exposure to
noise. However, well-defined studies of other noise-related health effects
in the work environment are required in order to determine borderline
values. By including conditions more directly related to reduced
well-being, e.g. the quality of a person’s sleep and sickness absence, and
productivity it will be possible to provide a better foundation for
evaluating the effects of noise.
About the report
The report “Helbredseffekter af støj i arbejdsmiljøet” (in Danish) can be
downloaded from http://www.arbejdsmiljoforskning.dk/upload/dok13.pdf.
Further imformation
Please contact Karin Sørig Hougaard, researcher at the National institute
of Occupational Health. Phone +45 39 16 52 17.
