2.2. Protection against noise, infra- and ultrasound
Protection against noise is achieved by the development of noise-proof technology, the use of means and methods of individual and collective protection, construction and acoustic methods. The means of collective protection are divided in relation to the source of noise to reduce noise in the source of occurrence (most effectively) and reduce noise on the pathways of its propagation. The following protection methods are distinguished by the implementation method:
o acoustic - based on the acoustic calculation of the room and the selection according to the principle of the means of sound insulation, sound absorption, vibration isolation, damping, noise silencers
o construction and acoustic screens, soundproofing, surveillance booths, remote control, casings, seals, etc. The most effective are such soundproof materials as triplast (composite material) and plastobetones with fillers made from cotton, sawdust of wood, straw, etc. Sound-absorbing materials are also marble, concrete, granite, brick, fiberboard, particle board, felt, mineral wool, materials with slotted perforations;
o architectural and planning - rational placement of workplaces; rational mode of work and rest.
Infrasound - oscillations with a sound wave frequency of less than 25 Hz. The nature of the occurrence of infrasonic vibrations is the same as that of audible sound, so the infrasound obeys the same laws and uses the same mathematical apparatus for its description as for audible sound (except for the concept associated with the sound level).
Infrasound is little absorbed by the medium, therefore it spreads over considerable distances.
The source of infrasound is equipment that operates at a cycle rate of less than 20 per second.
Infrasound adversely affects the central nervous system and can cause fear, anxiety, a feeling of wiggling, etc.
The range of infrasonic waves coincides with the internal frequency of individual human organs (6-8 Hz), therefore, due to resonance, severe consequences can occur. Increasing the sound pressure to 150 dBA leads to a change in digestive functions and heart rhythm. Possible loss of hearing and vision.
1) reducing infrasound in the source of occurrence;
2) the use of personal protective equipment;
3) use of devices that absorb infrasound. Monitoring instruments - sound level meters SHVK with filter FE-2; vibroakkusticheskaya equipment type RFT.
Ultrasound is the oscillation of a sound wave with a frequency of more than 20 kHz (outside of audibility). Low-frequency ultrasonic vibrations are propagated by air and contact; high-frequency - by contact. Ultrasound has a harmful effect on the cardiovascular, nervous and endocrine systems; disturbs thermoregulation and metabolism. Local effects can lead to numbness.
1) using locks;
2) sound insulation (screening);
3) use of remote control;
4) the use of anti-noise.
As control devices, a vibro-acoustic system of the RFT type is used.
Ultrasound as an elastic wave does not differ in properties from audible sound, but the frequency of the oscillatory process contributes to greater damping of oscillations due to the transformation of energy into heat.
On the frequency spectrum, ultrasound is divided into low-frequency and high-frequency; by the method of propagation - by air and contact ultrasound.
Low-frequency ultrasonic vibrations spread well in the air. The biological effect of their effect on the body depends on the intensity, duration of exposure and the size of the surface of the body subjected to the action of ultrasound. The prolonged systematic influence of ultrasound propagating in the air causes functional disorders of the nervous, cardiovascular and endocrine systems, auditory and vestibular analyzers.
Those who work on ultrasound devices have severe asthenia, vascular hypotension, decreased electrical activity of the heart and brain, a sense of fear in the dark, in a limited space, sudden attacks with increased heart rate, excessive sweating, spasms in the stomach, intestines, gallbladder. The most typical complaints are severe fatigue, headaches and a feeling of pressure in the head, difficulty in concentrating, inhibiting the thought process, insomnia.
The contact effect of high-frequency ultrasound on the hands leads to a violation of the capillary circulation in the hands, reducing pain sensitivity, i.e. peripheral neurological disorders develop. It is established that ultrasonic vibrations can cause changes in bone structure with a decrease in bone density.
Occupational diseases are registered only when ultrasound is hand-delivered to the hands.
It should be noted that the production noise and vibration have a more aggressive effect than the ultrasound of comparable parameters.
People and animals can be affected by a shock wave. Direct impact occurs due to excessive pressure and high-speed air pressure. In view of the small size of the human body, the shock wave immediately envelops the person and exposes him to strong compression for a few seconds.
The instant increase in pressure is perceived by the living organism as a sharp blow. High-speed head thus creates a significant head pressure, which can lead to the movement of the body in space. Indirect damage to people and animals can occur as a result of shocks of glass, slag, stones, wood and other objects flying at high speed.
The degree of impact of the shock wave depends on the power of the explosion, the distance, weather conditions, location (in the building, in the open area) and the position of the person (lying, sitting, standing). It is characterized by light, medium, severe and extremely severe injuries.
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