“Noise is defined as any unpleasant or annoying auditory sensation, any acoustic event producing this sensation, any sound of random nature with no defined components.” AFNOR
Sound is a rapid variation in pressure, called acoustic pressure, around the atmospheric pressure. Noise is a mixture of unwanted sounds of different intensities and frequencies perceived as an annoying or unpleasant experience. The audible human range, in terms of acoustic pressure amplitude, is from 20 µ Pa to 20 Pa and in terms of frequency from 20 Hz to 20,000 Hz.
Noise is measured in decibels (symbol: dB), a logarithmic ratio defined as follows:
Lp: acoustic power level
Peff: effective acoustic pressure (Pa)
P0: reference acoustic pressure: 2.10-5 Pa
Noise can be perceived as a simple inconvenience but also as a genuine aggression depending on the individual and, for the same person, depending on factors such as fatigue, stress etc. and neighbourly relations. This is a concern for local residents who demand that their well-being be respected and for operators who must control these nuisances.
Hazards and exposure limit values
The effects of noise on man are, by increasing order of noise level: inconvenience, fatigue, psychopathological disorders and hearing loss.
Inconvenience, which corresponds with relatively low noise levels, is the main consequence of the noise encountered in the environment.
Regulatory requirements in terms of classified installations aim at preventing inconvenience and do not tackle other aspects.
Psychopathological disorders can range from irritability or sleep disorders to genuine pathologies such as high blood pressure.
For example, a noise level of 85 dB(A) is considered as the exposure limit value in a working environment, below which no durable side effect on the hearing system is observed. Beyond this value, there is a risk of deafness depending on the duration and level of exposure (for example a 3 hour exposure to 105 dB(A) is equivalent, in terms of risk to hearing, to approximately 5 working weeks at 85 dB(A))
Above the 105 dB(A) threshold, there is pain and the risk of irreversible side effects (deafness) is significant.