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ACOUSTIC CONTAMINATION





Noise produces negative effect on human organism and first of all on central nervous system and cardio-vascular system. Long time exposure to noise may bring to hearing worsening and sometimes to deafness. In occupational conditions long noise exposure can cause accident, occupational disease, work capacity lowering.

In noisy conditions work production lowers down to 60%, and errors grow at 50%. Necessity to speak load effects mental activity. It’s a proven fact that for 30% of people noise is the cause of early aging.

For successful noise control it’s important to know its physical nature, its generating and distribution.

Noise is a type of sound that tends to sound unpleasant.

As a physical phenomenon noise is chaotic composition made up of many sounds with different unrelated frequencies and intensities.

The basic physical characteristics of noise are frequency, pressure and intensity.

Sound frequency is number of sound wave oscillations per second measured in hertz (Hz). Sound spectrum is divided into three diapasons:

- infra sound with frequency lower 20 Hz;

- sound with frequency within 20 - 20000 Hz;

- ultra sound with frequency over 20000 Hz.

Human ear can respond to sound in frequency spectrum from 20 to 20000 Hz. This sound diapason is divided into:

- low frequency – under 400 Hz;

- medium frequency – from 400 to 1000 Hz;

- high frequency – over 1000 Hz.

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. The street noise level is determined by intensity, speed and character of traffic, and also depends on the construction factors (structure of the streets, height and density of buildings), road cover and green plantings. On the territory of industrial cities cars make significant noise level, which spreading over the territory close to roads gets into dwellings. There following methods for reduction of noise influence on environment are recommended: decreasing of traffic speed and its restriction for some types of cars on certain roads in definite time; motor transport development; improvement of buildings soundproofing and construction of noise struggling screens along high-ways.



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. Reduction of tram noise level is possible improving condition of tram-line, and also modification of car construction.

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.

Regulation of noise for city building is carried out with the noise standard. For example, for apartments and rooms noise standard makes 30 dBA, class rooms - 40 dBA. These standards are indicated for night time (from 11 p.m. to 7 a.m.), and in day time standards are increased for 10 dBA.

City-planning measures on noise reduction include: increasing of distance between protected object and source of a noise; using of acoustic screens - slopes, walls, screen-structures; rational placing noisy and protected objects; using earth relief, deepening of highways; using free building construction (places where people stay temporarily: shops, dining rooms, ateliers serve as screen-building situated in front of the streets and apartment houses are placed behind them); trees planting.

 





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