It is well known that noise can cause a range of health injuries, the most serious, known and studied of which is hypoacusis, i.e. hearing loss of various degrees. Furthermore, noise can act through a complex mechanism also on other organs and systems (cardiovascular system, endocrine system, central nervous system and others), with many consequences, including the onset of mental fatigue, the reduction of efficiency and of performance at work, interference with sleep and rest and many others.
Also not to be neglected are the possible effects on safety: indeed, noise can lead to a masking effect that disturbs verbal communication and the perception of warning signals, thus increasing the risk of accidents at work.
In the EU 28% of workers (more than 60 million people) state that they are exposed to levels of noise that are so high as to make conversation difficult. Nearly 40 million workers have to raise their voices to be heard for at least half of the time that they are at work.
The Directive 2003/10/EC establishes the measures for prevention and protection against occupational noise exposure, in particular for preventing hearing damage.
EXTRA-AURAL EFFECTS OF NOISE
Specific assessment criteria for preventing these effects are still not defined.
Noise can interfere with mental activities that require attention, memory and capability of addressing complex problems. The adaptation strategies enacted to "cancel" noise and the effort required to keep the performances are associated with an increase of blood pressure and with high blood levels of stress-related hormones. These effects may have serious consequences on health and entail, depending on the individual conditions of the exposed subject, the onset of:
Cardiovascular problems: Hypertension and increased risk of heart attack: Extensive and documented evidence highlights the correlation existing between noise exposure and the onset of ischemic heart disease and hypertension, starting at exposure levels of 65-70 dB(A) LAeq.
Weakening of immune defences
Words are 100% understandable at background noise of about 45 dB(A) LAeq. At levels of background noise above 55 dB(A) LAeq (average level reached by unaltered voice) it is necessary to raise the voice.
The excessive background noise interferes with the capability of concentrating and induces an altered voice, thus increasing ambient background noise.
In classrooms and in conference rooms that are attended by children (who are particularly sensitive to the effects of noise) and the elderly (who often suffer with hearing reduction) background noise should be 10 dB(A) LAeq lower than the voice of the teacher or of the speaker.
EFFECTS ON LEARNING
It is now well demonstrated by international studies that children exposed to chronic noise can display attention deficits. It seems that they develop, in order to deal with the distracting effect of noise, learning strategies that cause psychophysical stress. Several studies have also documented a connection between noise and educational outcomes, especially in reading. Chronic noise has a negative impact on reading capability, whereas acute noise seems to have little effects. Furthermore, the capability in speaking seems also correlated to capability in reading, and thus noise would be related to both.
REST AND SLEEP
Noise can disturb sleep, inducing difficulties in falling asleep, reduction of the deep sleep phase, increase in the number of awakenings and adverse effects after the awakening or after an inadequate rest, such as fatigue and performance deficits. These effects can be avoided if the background sound levels in the indoor environment dedicated to rest are kept below 30 dB(A) LAeq, or have a maximum peak level below 45 dB(A) LAeq. These criteria should be strictly observed in working environments intended for the rest shift of workers.
PSYCHOLOGICAL AND BEHAVIOURAL EFFECTS
Annoyance and discomfort caused by noise considerably increase depending on the extent of noise: the majority of human beings are annoyed by noise levels at about 50 dB(A) LAeq. Loud noise increases aggressiveness and the incidence of aggressive behaviours in predisposed individuals.
At exposure levels above 80 dB(A) LAeq instinctive reflexes in response to danger are reduced, with possible consequences to safety.