Acute Effects:
These effects depend upon pressure and frequency.
At very high levels, e.g., 150 dB, immediate permanent hearing damage can be caused.
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At lower levels 100+ dB, nausea, loss of physical control and physiological changes, caused by stress, are noticed. These effects cease with the noise, although, in some cases, after a time delay.
Chronic Effects:
The principal chronic effect is that of noise induced hearing-loss. For this, there is one rule: ‘a person, exposed to high noise levels, goes deaf more quickly than he would otherwise have done’.
This effect depends upon the pressure, frequency, and time of exposure, becoming more rapid as the pressure rises, and, generally, more damaging with high frequencies. The loss starts, in the frequency range, around 4000 Hz, irrespective of the frequency of the source, causing the damage, and is more marked with impulsive noises.
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There are two components to the hearing loss:
The temporary and permanent threshold shifts expected percentage risk as a function of continuous sound level at work in dBA and years of exposure.
Mental Health:
There is very little specific evidence of the onset of mental or nervous illness caused by noise. There are some temporary effects such as lack of concentration and, at high levels, mental disorientation. There is also a real risk of the aggravation of an existing condition.
Communications:
Noise interferes with communications based upon sound when the frequency of the interfering noise coincides, approximately, with that of the desired sound.
Working Efficiency:
Loud continuous noise interferes with working efficiency and causes the incidents of errors to rise.
Industrial Accidents:
In so far as noise interferes with sound communication, it may mask warning signals, and, thereby, increasing, at the same time, the incidence of errors which may make accidents more likely.
Personal Comfort:
The effect depends upon the pressure and frequency and on the time of exposure. At levels well below those which cause rapid hearing damage, noise becomes intrusive, in termers with speech communication and with peaceful enjoyment of leisure.
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The last three effects are essentially a nuisance. It is difficult to assess, varies very much from individual to individual and becomes tolerable with continuous exposure. Total and impulsive characteristics and intermittency modify individual reactions.
The National Environment Policy Act of 1969 has required, since January 1, 1970, that federal agencies consider noise as an influence on the quality of environment. This has been implemented in the form of environmental impact statements required on all federal actions significantly affecting the human environment.
In April 1972, the Federal Highway Administration (FHWA) issued the Policy and Procedure Memorandum (PPM) 00.5 which compatible with different land uses.