Acoustic contamination

Anthropogenous energy contamination of environment

LEC 6

Energy contaminators of environment are considered such types of energy of anthropogenous origin, which are either absolutely not inherent for nature or their intensities considerably exceed background (natural) magnitudes and harmfully act on people, vegetative and animal organisms and can disturb normal functioning of various ecological systems.

The energy contaminators influence on the biosphere. They are thermal, radioactive (ionizing), electromagnetic and acoustic contaminators (noise, vibration). Each of these types has its own properties, parameters, risk rate for a person and other living organisms.

Noise, vibrations behave to harmful occupational factors, which during the prolonged influence on workers may cause heavy professional diseases. Frequently these factors accompany one to another. Mechanical oscillations lie in base of their origin, they are spreading in compressible medium. There is definite similarity in impact of noise, ultra- and infra- sound and vibrations on human organism, although some essential distinctions are observed.

Noise – disorderly combination of sounds, undesirable for human being, interfered with labor activities or rest.

Sound– wave mechanical motion of particles in compressed medium with oscillation frequencies in range between 16 and 20000 Hz. A frequency range over 20 kHz conforms to ultra-sound, and beneath 16 Hz – to ultra-sound.

Vibration – mechanical oscillations of elements of the constructions, equipment, engines, buildings, that are spreading in compressible medium and influencing on human being at superficial contact.

The main sources of noise in cities and other settlements are motor transport, railway and air transport and industrial plants. The motor transport creates the noise level from 82 to 95 dBA on the streets. Significant noise level is created by the railway transport: the electrotrain - 93 dBA, passenger train - 91 dBA, freight train -92 dBA on distance of 7,5 m from the moving train. Noise levels in subway open lines reaches 70-80 dBA. The most noisy among all the types of the city transport is tram. The moving tram creates noise loading (10 dBA higher than car wheels) when engine is on and doors operating. The air transport creates sound equivalent to levels of 80 dBA, and maximum level reaches 108 dBA. For noise minimizing special piloting on takeoff and landing, more steep trajectories, low power setting, rational organization of air movement (take-off and landing strip not crossing localities), rational planning etc are used.

Normalization of noise for city building is carried out in correspondence with the standard «СНиП: Защита от шума». For example, for apartments and rooms norm makes 30 dBA, class rooms - 40 dBA. These norms are indicated for night time (from 11 p.m. to 7 a.m.), and in day time norms are increased for 10 dBA.

Noise acting on hearing organ, central and vegetative nervous systems, and through them on internal organs of human body the noise may cause a noise illness. Bringing general organism resistibility down by this external influence, noise assists in development of infections diseases. At work in noise conditions a raised fatiguability and lowering of work capacity, attention and verbal commutation become worse, the preconditions to erroneous acts of the workers are created. Noise creates the preconditions to worsening of psychological state also.

Noise illness may be subdivided on specific affects, developed in peripheral part of human auditory system (organ Corti), and unspecific ones, typical for other human organs and body systems.

Noise changes the functional state of most part of the human systems and organs because of their interaction over c.n.s. Such intercommunication brings about impact of noise on human sight organs, vestibular vehicle and motion functions, in particular, a decrease of muscle strength.

As a result of vibration influence disease may develop. For man, that is exposed to general powerful vertical vibration, the vessels of cerebrum and envelopes may be damaged, and blood circulation be disturbed also.

Vibration from hand vibration instruments can be followed with damage of small blood-vessels and nervous finishing in muscles and general or local – determines forms of vibration disease, among them next three are distinguished: peripheral, cerebral and centrally-peripheral.

By first symptom of peripheral form of disease becomes a sense of dumbness in hands. Patient feels a burning, rheumatic pain in hands and legs. Headache, heaviness and noise in head are the first signs of cerebral form of disease. Momentary dizziness’s and sometimes – swoon are possible also. Patient becomes irritable his sleep is disturbed, the vessels spasms arise. As result a high blood pressure (hypertension), general weakness, shaking of hands may develop.

Protection from noise and vibration.

1) Reduction in source provides and reduction along propagation path.

2) Design of new low-noise engine and modification of the engines being in operation.

3) Means of individual protection from noise and vibration – anti-noise helmets, headphones and ear-plugs, noise-protective combination.

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