- - methods for reducing noise at the source of its formation;
- - methods for reducing noise along the path of its propagation;
- - personal protective equipment against noise.
Reducing noise at the source of its formation is achieved by constructively changing the source.
This is the replacement of reciprocating motion with rotational motion. Improving the quality of balancing of rotating parts. Improvement of lubrication and frequency class of rubbing surfaces. Replacing gears with hydraulic ones.
Methods to reduce noise along its propagation path include:
- - acoustic treatment of premises;
- - isolation of noise sources or premises from noise penetrating from outside;
- - use of noise suppressors.
Acoustic treatment of premises means the lining of part of the internal surfaces of fences with sound-absorbing materials, as well as the placement of piece absorbers in the room, as well as the placement of piece absorbers in the room - these are freely suspended volumetric absorbing bodies of various shapes. Sound-absorbing linings are placed on the ceiling, in the upper parts of the walls at a room height of no more than 6/8 m so that the acoustically treated surface is at least 60% of the area of the surfaces delimiting the room.
Additional piece absorbers are hung near the noise source if the room area is small.
Isolation of noise sources includes such means as soundproofing casings, fences, and screens.
Soundproofing barriers allow you to isolate a noise source or room from noise penetrating from the outside by creating a sealed barrier to the propagation of airborne noise for each active frequency band.
On automated lines, where it is impossible to isolate a person from the source of noise for a long time, soundproofing booths are installed.
If it is not possible to completely isolate either the noise source or the person using booths, then acoustic screens are installed along the path of noise propagation.
Flat screens are effective in the range of direct sound, starting at a frequency of 500 Hz.
Concave screens of various shapes are also effective in the area of reflected sound, starting from a frequency of 250 Hz. The dimensions and location of the screen are determined depending on the excess of the noise spectrum at the design points above the standard values.
Silencers are used for air intake and exhaust in air ducts, diesel and compressor units.
According to the principle of operation, silencers are divided into active (dissipative) type and reactive (reflective) type.
In active type silencers, noise reduction is achieved by converting sound energy into heat in sound-absorbing material placed on the internal cavities.
In reactive type mufflers, noise is reduced by reflecting the energy of sound waves in a system of expanded and resonant chambers connected to each other by the volume of the air duct using pipes and holes.
The chambers can be lined inside with sound-absorbing material, then in the low-frequency region they work as reflectors, and in the high-frequency region as noise absorbers (combined silencers).
The type and dimensions of mufflers are selected depending on the amount of noise reduction required, taking into account its frequency from tabulated acoustic efficiency data. The third method of dealing with noise is the use of personal protective equipment:
- - insert - these are soft tampons inserted into the ear canal made of ultra-thin fiber impregnated with a mixture of wax and paraffin and hard inserts (ebonite, rubber) in the shape of a cone. These are the cheapest, but quite effective and convenient means (noise reduction by 5/20 dB);
- - headphones - fit tightly around the ears and are held in place by an arched spring. Effective at high frequencies;
- - helmets - are used when exposed to noise levels of more than 120 dB, when the noise acts directly on the human brain, and earbuds and headphones do not provide the required protection.
The fight against noise is one of the most pressing problems of our time. By acting on the central nervous system, noise causes fatigue, insomnia, and inability to concentrate, which lead to decreased productivity and accidents. With constant irritating exposure to noise, mental disorders, cardiovascular diseases, peptic ulcers, and hearing loss can occur. Noise can affect hearing in a variety of ways: cause instant deafness or damage to the hearing organ (acoustic trauma); with prolonged exposure, sharply reduce sensitivity to sounds of certain frequencies or reduce sensitivity for a limited time - minutes, weeks, months, after which hearing is restored almost completely. Long periods of continuous exposure to high-intensity noise are most harmful to hearing. If a person is exposed for several minutes to medium or high frequency sound with a level of about 90 dB, then he experiences a temporary shift in the threshold of audibility. As the exposure time increases and the noise level increases, the time shift in the threshold increases and the recovery period lengthens.
People react differently to noise. The same dose of noise exposure causes hearing damage in some people, but not in others, and the damage may be more severe in some than in others. Noise is a type of sound. Sound is the vibration of the medium (solid, liquid or gaseous) in which it travels. The sound characteristics available for measurement include: intensity - I, sound pressure - R and speed - v. Sound intensity (W/m2) is characterized by the flow of energy carried by sound per unit area.
The relationship between sound intensity I and sound pressure R is this:
where p is sound pressure (the difference between the instantaneous value of the total pressure and the average value of pressure that is observed in the medium in the absence of a sound field), Pa; ρ - density of the medium, kg/m3; s is the speed of sound in the medium, m/s.
The intensity of the weakest (10 W/m2) audible sound is 10 -12 W/m2. The highest sound intensity we encounter without risking life is the noise of a jet airplane. It is difficult to compare the given values due to the huge difference. Therefore, to measure sound intensity and parameters such as sound pressure and power, a relative logarithmic unit called sound pressure level or intensity level is introduced.
Sound intensity level
where Iо is the sound intensity corresponding to the threshold level (Iо = 10 -12 W/m2).
Sound level is measured in decibels (dB). Since sound level is a logarithmic relative value, when sound intensity doubles, the intensity level increases by 3 dB. If there are n identical noise sources, the overall intensity level
The human ear and many acoustic devices respond not to sound intensity, but to sound pressure. Sound pressure level
where po is the threshold sound pressure (po=2X10 -5 Pa).
The relationship between intensity level and sound pressure level follows from the formula
where ρо and Co are the density of the medium and the speed of sound under normal atmospheric conditions, i.e. at t=20°C, po=10 5 Pa.
When noise propagates under normal atmospheric conditions, Li=Lp. The noise levels are given in table. 4.3.
One of the most significant issues in noise research is the behavior of sound depending on frequency. The lower limit of human perception of sound is about 20 Hz, and the upper limit is about 20,000 Hz. The dependence of sound level on frequency is called the shulsh frequency spectrum. Determining the sound intensity for each frequency would require an infinite number of measurements, so the entire possible frequency range is divided into octaves and the geometric mean value of the frequency is calculated for each octave.
Table 4.3. Levels of different sounds depending on noise source and distance
| Noise source | At a distance, m | Level, dB |
| Living room | - | 35 |
| Medium volume speech | 1 | 60 |
| Typewriting Bureau | - | 65 |
| Metal cutting machines | At work | 80...96 |
| Diesel truck | 7 | 90 |
| Jackhammer | 1 | 100 |
| Jet engine | 25 | 140 |
The boundary and geometric mean (within these boundaries) frequencies are given below:
Depending on the frequency at which the maximum sound pressure is located, the nature of the spectrum can be low-frequency (maximum below 300 Hz), mid-frequency (maximum in the region of 300...800 Hz) and high-frequency (maximum above 800 Hz).
By nature, noise spectra can also be divided into broadband and tonal. Broadband noise has a continuous spectrum more than one octave wide, meaning that each octave frequency has a corresponding noise level.
Rice. 1. Limit noise spectra
This type of noise is typical for fans. The spectrum of tonal noise contains individual discrete components. A similar spectrum has, for example, the noise created when working with a circular saw. The distribution of standard sound pressure levels by frequency represents the limiting spectrum. In Fig. Figure 1 shows the limit spectra for rooms of various types: 1 - residential rooms; 3 - hospital areas, doctors’ offices, hotel rooms; 4 - educational premises; 5 - territories of residential buildings, children's and school playgrounds; 6 - premises of design, design and research organizations 7 - theater foyers, restaurant halls; 8 - management workplaces, computer centers; 11 - permanent workplaces in production premises, in the cabins of road construction, earthmoving and other similar machines.
Amendments should be introduced to the standard noise levels, depending on the nature of the noise and the duration of its exposure (Table 2). The noise level obtained taking into account the amendments is called acceptable.
Projects for the construction of a particular facility must reflect all noise reduction measures, confirmed by appropriate acoustic calculations, which are carried out at the stage of the technical design for a complex of structures or for an individual facility.
Rice. 2. Paths of noise propagation in a building
Acoustic calculation is as follows: identify noise sources and determine their noise characteristics; select points in the premises and territory for which acoustic calculations should be carried out; determine acceptable sound pressure levels for these points; identify the paths of noise propagation from sources to design points; determine the expected sound pressure levels at design points before implementing noise reduction measures; determine the required noise reduction; designs are selected and calculated to provide the required noise reduction.
Required reduction in sound pressure level ALTp at the design point
where Li is the expected sound pressure level created by the source, dB; Lnon - permissible sound pressure level, dB; n is the number of noise sources taken into account.
The paths of noise propagation in buildings are varied (Fig. 2). Noise penetrates through the enclosing structures, the sound, repeatedly reflected from walls, ceilings, objects, is significantly amplified and increases the overall noise level in the room.
The cause of noise can be mechanical, aerodynamic and electromagnetic phenomena. Mechanical noise is caused by impact processes, friction in machine parts, etc. Aerodynamic noise occurs during the flow of liquid or gas, and electromagnetic noise occurs during the operation of electrical machines and equipment.
The fight against noise is carried out: by technical means that reduce the noise of machines and equipment at the source of its formation, changing technological processes; construction and acoustic measures; remote control device for noisy units; organizational events; use of personal protective equipment.
Reducing noise at the source of its formation is most rational and is achieved by improving the design of machines, using materials for machine parts that do not emit strong sounds, ensuring minimum tolerances in the joints of parts, using lubricants, etc. The effectiveness of such measures to reduce noise levels (dB) is given below :
Construction and acoustic measures consist of rational planning of premises and buildings, reducing noise along the path of its propagation and treating the internal surfaces of premises with sound-absorbing materials. With a rational layout of premises, the noisiest workshops should be concentrated in one or two places and separated from quiet rooms by breaks or rooms in which people spend a short time. In workshops with noisy equipment, proper placement of machines is necessary. They should be located in such a way that increased noise levels are observed in the smallest possible area. Between areas with different noise levels, partitions are installed or utility rooms, warehouses for raw materials, finished products, etc. are located. For enterprises located within the city, the noisiest rooms are located in the depths of the territory. Noise reduction in residential areas is carried out both by architectural and planning solutions (breaks, construction methods) and by installing noise protection structures (screens, noise protection strips for landscaping). Profiles of streets with noise screening structures are shown in Fig. 3.
Fig. 3. Protection from traffic noise by:
a - buildings; b - embankments; c - slope
A significant reduction in noise is observed when a screen is installed in the path of its propagation. At the same time, a sound shadow appears behind the screen.
In industrial premises, the sound level increases significantly due to its reflection from building structures and equipment. To reduce the proportion of reflected sound, a special acoustic treatment of the room is used, which consists of lining the internal surfaces with sound-absorbing materials.
When sound energy Epad falls on any surface, part of the sound energy is absorbed - Epog, and part is reflected - Eotr. The ratio of absorbed energy to incident energy is the sound absorption coefficient of this surface:
Sound absorption by materials is caused by internal friction in the material and the transition of sound energy into thermal energy. The sound-absorbing properties of a material depend on the thickness of the absorbing layer, the frequency of sound incident on it and the type of material. Structures with α greater than 0.2 are considered sound-absorbing.
Sound-absorbing structures are divided into three groups: porous sound-absorbing; resonant; piece sound absorbers. In construction practice, porous sound-absorbing materials are most often used (Fig. 4, a). Structures made from them are made in the form of a layer of the required thickness, mounted on the fence or indented from it. Resonant structures are perforated screens covered with fabric on the reverse side. They have maximum sound absorption in a certain frequency band, so the necessary sound absorption parameters must be accurately calculated for them (Fig. 4, b).
Rice. 4. Sound-absorbing linings:
a - porous; b - resonant; 1 - fastening; 2 - sound absorber; 3 - enclosing structure; 4 - perforated screen 
Rice. 5. Volumetric sound absorbers:
a - design; b - layout diagram; 1 - frame; 2 - suspension point; 3 - shell; 4 - sound absorber
Piece sound absorbers are volumetric sound-absorbing bodies, for example cones, prisms, parallelepipeds, suspended from the ceiling (Fig. 5).
The amount of noise reduction when using sound-absorbing cladding is 6...8 dB, which corresponds to a 1.5-fold reduction in volume.
One of the methods for reducing noise is the installation of sound-absorbing barriers (Fig. 6). The mechanism of sound transmission through such a fence is that a sound wave incident on the fence sets it into oscillatory motion with the same frequency. As a result, the enclosing structure itself becomes a source of sound. But the amount of emitted sound power is much less than the sound power incident on the fence from the side of the noise source, since most of the sound energy is reflected from the fence.
The soundproofing qualities of fences are characterized by the sound permeability coefficient
where I pr, p pr - intensity and sound pressure of the transmitted sound; I pad, p pad - intensity and sound pressure of the incident sound. 
Rice. 6. Soundproof casing:
1 - noisy unit; 2 - sound absorber; 3 - soundproofing fence; 4 - shock absorbers 
Rice. 7. Noise measurement circuit:
1 - measuring microphone; 2 - amplifier; 3 - frequency analyzer (filter); 4 - detector; 5 - indicator
In practice, it is more convenient to use the value of the soundproofing ability of the fence
For a single-layer homogeneous partition
where t is the mass of 1 m 2 of fencing, kg; f - sound frequency, Hz.
However, this dependence is valid only for a certain frequency range.
It is often impossible to reduce noise to acceptable limits. In these cases, it is necessary to use personal protective equipment - headphones, helmets or special earbuds that cover the ears.
The main instrument for measuring noise is a sound level meter. A schematic diagram of the measuring path is shown in Fig. 7.
Noise today is a universal hazard in the sense that it can penetrate into all spheres of everyday life and areas of our production, educational and social activities. Levels of natural and technical noise fluctuate within a fairly wide range from 10-30 dB (rustling leaves, human whisper) to 120-130 dB (lightning discharges in the celestial sphere, the launch of a jet aircraft at a distance of 50-100 meters). The presence of such a wide range of changes in sound pressure levels indicates that adaptation to it, according to modern concepts, can occur with both favorable and unfavorable outcomes.
When environmental factors influence a person, the main level of constancy of his internal environment is homeostasis, which means maintaining the relative dynamic constancy of the entire organism. The secret of the wisdom of our body is achieved precisely by homeostasis, i.e. perfect adaptive activity.
Noise can have both a specific effect on the organ of hearing and a nonspecific effect (mediated through the central nervous system) on the entire body. In the first case, there may be a temporary decrease in hearing thresholds, then a permanent decrease occurs, followed by hearing loss and complete deafness. In the second case, when exposed to weak noises, a training reaction is formed with its phases of orientation, restructuring and training; when exposed to moderate noise, an activation reaction develops with its phases of primary and persistent activation; When exposed to strong noise, a stress response is formed with its phases of anxiety, resistance and exhaustion. If the first two reactions (training and activation) indicate normal adaptation of the human body to noise, then the third reaction, being stressful, characterizes pathological adaptation to the sound stimulus with consequences for human health.
From a brief consideration of the consequences of the adverse effects of noise on the human body, it is clear that this harmful factor must be fought and fought seriously, using all possible ways to reduce its levels to acceptable values.
The German microbiologist Robert Koch, who discovered the causative agent of tuberculosis (the bacillus named after him), wrote the following about reducing noise levels: “Someday humanity will be forced to deal with noise as decisively as it deals with cholera and plague.”
To date, both in the Russian Federation and abroad, many approaches have been developed to reduce noise levels inside and outside homes, educational and medical premises, public buildings, as well as to reduce the levels of sound discomfort on the streets and open spaces adjacent to residential buildings. All these measures are divided into groups of measures that can be used to reduce noise levels, both at the sources of their formation and along the path of their propagation. The fight against noise at the source is carried out using engineering, technical, organizational and administrative methods, and along the path of noise propagation in the urban environment from the source to the protected object - using urban planning and construction-acoustic methods. In the noise protection facility itself, a reduction in sound levels is ensured by design and construction methods that increase the soundproofing qualities of the building envelope and structures and by planning methods.
Let's look at some of them in more detail.
Organizational and administrative measures
A significant reduction in traffic noise levels can be achieved by reducing the intensity and noise of traffic flows. For example, when organizing freight transportation, they determine the category of cargo (industrial, construction, consumer, fuel, city cleanup) and use special roads for their passage, bypassing city centers. Management transport flow also provides for ensuring the comfort of the population during the day and at night, forecasting the levels of transport noise in microdistricts under construction, reducing noise in more dangerous areas, and so on.
The system of organizational and administrative measures includes:
- improving road maintenance and using less noisy types of road surfaces;
- ensuring rational traffic speeds on highways;
- exclusion of vehicular traffic, especially freight transport, in the central areas of the city and on residential streets. This includes the construction of pedestrian zones, the removal of transit transport to bypass roads, the establishment of one-way traffic, restrictions on night traffic, etc.
- improving traffic conditions on stretches and intersections.
- maximum development of public transport in the city and increasing its competitiveness with individual vehicles in terms of speed and comfort, as well as the development of bicycle transport with the construction of bicycle paths for them
It should be emphasized that reducing the noise of ground transport through the use of noise-absorbing road surfaces is one of the very promising methods. At the same time, the composition and condition of the road surface significantly influences the noise characteristics. Thus, concrete pavement is 2-3 dB (A) noisier than asphalt pavement; in rain, flow noise can increase by 5-6 dB (A), and in snowfall it can decrease by 3-5 dB (A).
Urban planning and construction-acoustic measures
The bulk of noise reduction costs in developed countries is associated with the installation of noise protection structures, the most common of which in cities and on roads are acoustic barriers, and the main soundproofing barrier is double or triple acoustic protective windows. For example, in Germany over the past decade, the cost of installing acoustic barriers and protective windows has accounted for more than 90% of all costs for noise protection.
Soundproofing- this is the cheapest of all types of noise protection and at the same time acoustic efficiency is achieved (15-20 dB (A)), especially in the high and mid-frequency range. However, to reduce low-frequency noise, the use of soundproofing structures alone is often not enough.
Currently, dozens of different designs of acoustic screens are used, which can be divided into 5 main classes:
- wide acoustic screens;
- acoustic screens - walls;
- combined acoustic screens;
- hybrid acoustic screens;
- screen complexes.
Residential high-rise buildings, excavations, embankments, as well as non-residential buildings for various purposes can be considered as wide acoustic screens that provide noise reduction in residential buildings, both due to height and significant additional attenuation on the wide free edge of these screens. A very effective measure is the use of tunnels built by open casting or shield tunneling. In addition to reducing street noise, the use of underground space for laying highways improves the conditions of movement of the population and contributes to the formation of a healthy, comfortable and aesthetically attractive environment.
The most widely used are acoustic walls - screens that have a wide variety of designs and are made from various materials. So, simple walls can be made of concrete, wood and other materials. The main disadvantage of such structures is the presence of a sound-reflecting effect, which is enhanced if such structures are installed parallel to each other. The efficiency of screens of this type does not exceed 5-12 dB (A).
Acoustic screens with sound-absorbing material do not have these disadvantages. They are collapsible, usually made of metal. The main element of such screens is an acoustic panel filled with sound-absorbing material. This panel has slotted perforations on the sound source side. The presence of sorption material increases the efficiency of such panels by at least 3-5bdb (A). The required efficiency of screens of this type is ensured by varying their height, length, and distance between noise sources and the screen.
Promising is the use of combined acoustic screens, which combine the advantages of acoustic screens - walls and embankments or excavations. Their efficiency is extremely high without the additional costs associated with increasing excavation depth or embankment height.
Where it is necessary to achieve noise reduction over the entire frequency range (in hospitals, schools), it is advisable to use hybrid acoustic screens that combine the dampening properties of acoustic screens with sound-absorbing material and active noise suppressors that emit sound in antiphase to the noise being muffled.
Noise reduction measures using technical means.
Traditionally, the following methods are most effective for reducing external noise from cars:
- installation of noise silencers at the engine inlet and outlet;
- improving transmission quality;
- vibration damping of the gearbox;
- improving the quality of road surfaces;
- prevent tire wear;
- sound insulation and sound absorption of external sources of vehicle noise.
Green spaces play an important role in noise protection. Back in the Soviet Union, studies were carried out on the noise-absorbing properties of various tree species. Some of them, mainly deciduous, such as maple, poplar and linden, are from this point of view more advantageous than a brick or concrete wall.
Creating a belt of these trees in cities is beneficial because they not only trap dust and harmful chemicals, but are also an effective barrier against the spread of noise, which as a result is reduced by 7-9 dB (A) in the summer months and by 3-4 dB (A) in winter.
Measures to reduce aircraft noise
The most effective measures to combat aircraft noise are those taken during the design and construction of aircraft engines. The current state of technology makes it possible to re-equip older types of aircraft, achieving a reduction in the noise of their engines. But re-equipping a fleet of aircraft is too expensive. In the near future, we also cannot hope to create new designs that would be much quieter than currently accepted international standards allow.
You can use special techniques during takeoff and landing to reduce noise: rational layout of runways, reducing the number of night flights, as well as a general reduction in the number of flights due to the transition to heavy-duty modern airliner models. It is rational to create two protective zones at each airfield. In the first protection zone, the noise level averaged over the daytime at an equivalent level should not exceed Leq = 65 dB A, and for the night - no more than L eq = 55 dB A.
Reducing the noise level in a residential area to the recommended permissible level and reducing the sanitary gap zone can be achieved by planning, technological, technical and organizational technologies.
Bibliographic link
Nekipelova O.O., Nekipelov M.I., Maslova E.S., Urdaeva T.N. NOISE AS AN ACOUSTIC STRESSOR AND MEASURES TO COMBAT IT // Fundamental Research. – 2006. – No. 5. – P. 55-57;URL: http://fundamental-research.ru/ru/article/view?id=5032 (access date: 02/06/2020). We bring to your attention magazines published by the publishing house "Academy of Natural Sciences"
When developing technological processes, designing, manufacturing and operating machines, industrial buildings and structures, as well as when organizing a workplace, all necessary measures should be taken to reduce noise, ultrasound and vibration in the workplace to values not exceeding the permissible values specified in GOST 12.1. 003 and GOST 12.1.001.
These measures should be carried out: by technical means of noise control (reducing the noise of machines at the source; the use of technological processes in which sound pressure levels at workplaces do not exceed permissible; the use of remote control of noisy machines; automation of control of noisy machines; the use of sound-insulating enclosures, semi-enclosures, cabins; arrangement of interlocking systems that turn off ultrasonic source generators in case of violation of sound insulation, etc.); construction and acoustic measures; use of personal protective equipment; organizational measures (choosing a rational mode of work and rest, reducing the time spent in noisy conditions, therapeutic and preventive and other measures).
Areas with sound levels above 85 dB must be marked with safety signs. The administration is obliged to provide personal protective equipment to those working in these zones. Even short-term stay in areas with octave sound pressure levels above 135 dB in any octave band is prohibited.
Enterprises, organizations and institutions must ensure control of noise levels in the workplace and establish rules for safe work in noisy conditions.
Constructive and planning solutions to combat noise. Noise at the source can be reduced by increasing the manufacturing accuracy of individual machine components, reducing gaps, improving static and dynamic balancing of moving parts, replacing noisy materials with less noisy ones (steel gears with plastic ones), and installing noise suppressors. Silencers are divided into active ones, which absorb the sound energy entering them, and reactive ones, which reflect the energy back to the source.
Intense noise caused by vibration can be reduced by covering the vibrating surface with a material with high internal friction (rubber, asbestos, bitumen), while part of the sound energy is absorbed. The greater the density of adhesion of the material to the vibrating surface, the greater the absorption effect.
Sound absorption is caused by the conversion of vibrational energy into heat due to friction in the sound absorber. Materials with good sound-absorbing properties are relatively light and porous (mineral felt, glass wool, foam rubber). In small rooms, walls are lined with sound-absorbing materials. In large rooms (more than 300 m), cladding is ineffective, and in them noise reduction is achieved using sound-absorbing screens (flat and volumetric). Screens are placed near noise sources, and the noise reduction reaches 7-8 dB.
Sound insulation is a method of reducing noise by creating structures that prevent noise from spreading from one insulated room to another. Soundproofing structures are made of dense solid materials (metal, wood, plastics) that effectively prevent the spread of noise.
Noisy units can be isolated using soundproofing semi-casings, casings, cabins, which should be installed without rigid connections to the equipment. To increase the efficiency of sound insulation, the internal surfaces of the casings are lined with sound-absorbing materials.
Reducing the harmful effects of industrial noise on other buildings can be achieved by rational planning of workshops and the placement of green spaces on the territory of the enterprise.
Noise reduction using construction and acoustic measures. The main construction and acoustic measures to reduce sound pressure levels in workshops include: installation of equipment that produces noise at lower levels; installation of equipment and machinery in a separate room with increased sound insulation of structures and minimum sizes of required technological openings; installation of soundproof semi-enclosures, casings and cabins of closed and semi-open types for the operator (Figure 1), as well as soundproof shelters for support personnel, cabins for rest and remote control; installation of acoustic screens near the most intense noise sources; installation of vibration-absorbing coatings; installation of noise silencers in heating, ventilation and air conditioning systems, vacuum pumps, compressor units, segregation of drive equipment into a separate room or its partial isolation with the obligatory installation of sound-absorbing cladding in the area where drive equipment is located; installation of mufflers on technological conveyors for supplying wood from the debarking drum to the chipper; installation of receiving and discharge funnels for the chipper made of metals with a damping layer.
Reducing noise in industrial premises can be achieved by localizing it near the source with soundproof casings, booths, and chambers.
Personal noise protection equipment. The use of personal protective equipment is advisable in cases where active methods either do not provide the desired acoustic effect or are uneconomical, as well as during the development of basic noise reduction measures.
Personal noise protection equipment includes earplugs, headphones, helmets - they can reduce noise by up to 40 dB.
Sheet
Introduction 3
1. Harmful effects of noise on the human body 4
2. Sources of industrial noise and methods to combat them 6
3. Collective protective equipment 8
4. Personal protective equipment 9
Literature 13
Introduction
Reducing noise in human activity is becoming an urgent problem. Among all the noise that affects humans, industrial noise stands out. The level of industrial noise has increased significantly. This is caused by the use of high-performance machines and mechanisms and an increase in operating speeds. One of the most common types of industrial noise is mechanical noise. This noise levels reach 120 dB. In many industries, impulse and impact noise predominates, which are considered very harmful. Unexpected and shocking noises can cause a startle reaction and inappropriate behavior. The peculiar negative effect of impact noise can cause an increase in blood pressure, respiratory rate, sinus arrhythmia and reduce mental performance.Noise harms not only people's health, but also the country's economy. Thus, people engaged in work of mental intensity made almost twice as many errors against a background noise of 70 dB as in silence. The performance of those engaged in mental work drops by approximately 60%, and in physical work by 30%. Impact noise is most typical for industry (metallurgy, mechanical engineering, transport) and causes the collision of machines and mechanisms during operation. This problem is one of the most pressing problems associated with assessing the behavior of various structures under the influence of intense impulsive loads that arise during the operation of modern equipment. Analysis of literature data showed that the most common method of research is on models of collision processes in laboratory conditions with the aim of developing materials and structures with increased damping characteristics and low sound emission.
1 Harmful effects of noise on the human body
The manifestations of the harmful effects of noise on the human body are very diverse.
Long-term exposure to intense noise (above 80 dBA) on a person’s hearing leads to partial or complete loss of hearing. Depending on the duration and intensity of noise exposure, a greater or lesser decrease in the sensitivity of the hearing organs occurs, expressed as a temporary shift in the hearing threshold, which disappears after the end of noise exposure, and with a long duration and (or) intensity of noise, irreversible hearing loss (hearing loss) occurs, characterized by permanent changing the hearing threshold.
There are the following degrees of hearing loss:
I degree (mild hearing loss) – hearing loss in the area of speech frequencies is 10 - 20 dB, at a frequency of 4000 Hz - 20 - 60 dB;
II degree (moderate hearing loss) – hearing loss in the area of speech frequencies is 21 - 30 dB, at a frequency of 4000 Hz - 20 - 65 dB;
III degree (significant hearing loss) – hearing loss in the area of speech frequencies is 31 dB or more, at a frequency of 4000 Hz – 20 - 78 dB.
The effect of noise on the human body is not limited to the effect on the organ of hearing. Through the fibers of the auditory nerves, noise irritation is transmitted to the central and autonomic nervous systems, and through them it affects the internal organs, leading to significant changes in the functional state of the body, affecting the mental state of a person, causing a feeling of anxiety and irritation. A person exposed to intense (more than 80 dB) noise spends on average 10–20% more physical and neuropsychic effort to maintain the output achieved at a sound level below 70 dB(A). An increase of 10–15% in the overall incidence of workers in noisy industries was established. The effect on the autonomic nervous system is manifested even at low sound levels (40 - 70 dB(A). Of the autonomic reactions, the most pronounced is a violation of peripheral circulation due to narrowing of the capillaries of the skin and mucous membranes, as well as an increase in blood pressure (at sound levels above 85 dBA).
The impact of noise on the central nervous system causes an increase in the latent (hidden) period of the visual motor reaction, leads to disruption of the mobility of nervous processes, changes in electroencephalographic parameters, disrupts the bioelectric activity of the brain with the manifestation of general functional changes in the body (even with noise of 50 - 60 dBA), significantly changes the biopotentials of the brain, their dynamics, causes biochemical changes in the structures of the brain.
With impulsive and irregular noise, the degree of noise exposure increases.
Changes in the functional state of the central and autonomic nervous systems occur much earlier and at lower noise levels than a decrease in auditory sensitivity.
Currently, “noise disease” is characterized by a complex of symptoms:
- decreased hearing sensitivity;
changes in digestive function, expressed in decreased acidity;
cardiovascular failure;
neuroendocrine disorders.
Ultrasounds (above 20,000 Hz) also cause hearing damage, although the human ear does not respond to them. Powerful ultrasound affects nerve cells in the brain and spinal cord, causing a burning sensation in the external auditory canal and a feeling of nausea.
No less dangerous are the infrasound effects of acoustic vibrations (less than 20 Hz). At sufficient intensity, infrasounds can affect the vestibular system, reducing auditory sensitivity and increasing fatigue and irritability, and lead to loss of coordination. A special role is played by infrafrequency oscillations with a frequency of 7 Hz. As a result of their coincidence with the natural frequency of the alpha rhythm of the brain, not only hearing impairment is observed, but internal bleeding may also occur. Infrasounds (6 - 8 Hz) can lead to cardiac and circulatory problems.
2 Sources of industrial noise and methods to combat them
Numerous studies have found that prolonged exposure to noise affects human health. Excessive noise exposure affects more than just hearing loss. The human hearing aid is just a gate through which noise enters the body and affects the human central nervous system. In everyday life and at work, a person “gets used” to noise and it seems to him that the noise bothers him to a lesser extent. However, this impression is deceptive - in reality, the harmful effects of noise continue regardless of whether a person pays attention to it or not. Moreover, this sometimes does not depend on the level and duration of noise exposure, but to a greater extent on the person’s condition at a given period of time.Noise reduces not only a person’s performance, productivity and quality of work, but also his safety.
The current standard in the Russian Federation 12.4.081-89 “Protective equipment for workers” is divided into collective and individual protective equipment. Collective protection means include combating noise at the source of its formation (that is, by creating low-noise equipment and using it in the production process) and combating noise along the path of its propagation. The second way is used when, based on known and technically feasible methods, it is not possible to reduce the noise level at this stage.
According to GOST 12.1.003-83, when developing technological processes, designing, manufacturing and operating machines, industrial buildings and structures, as well as when organizing workplaces, all necessary measures should be taken to reduce noise affecting humans to values not exceeding permissible values.
Protection from noise should be ensured by the development of noise-proof equipment, the use of means and methods of collective protection, including construction and acoustics, and the use of personal protective equipment.
First of all, collective protective equipment should be used. In relation to the source of noise generation, collective means of protection are divided into means that reduce noise at the source of its occurrence, and means that reduce noise along the path of its propagation from the source to the protected object.
Reducing noise at the source is achieved by improving the design of the machine or changing the technological process. Means that reduce noise at the source of its occurrence, depending on the nature of noise generation, are divided into means that reduce noise of mechanical origin, aerodynamic and hydrodynamic origin, and electromagnetic origin.
For sources of mechanical noise, noise reduction is ensured by replacing the reciprocating movement of parts with a rotational one, replacing impact processes with non-impact ones (riveting - welding, trimming - milling), improving the quality of balancing of rotating parts and the accuracy class of manufacturing parts, improving the lubrication of rubbing surfaces, and replacing materials.
To reduce aerodynamic noise, special noise-absorbing elements with curved channels are used. Aerodynamic noise can be reduced by improving the aerodynamic characteristics of vehicles. To combat noise generated by hydraulic shocks, it is necessary to properly design and operate hydraulic systems. Cavitation noise is reduced by improving the hydrodynamic characteristics of pumps and choosing optimal operating modes.
Reduction of electromagnetic noise is carried out through design changes in electromechanical systems.
3 Collective protective equipment
Methods and means of collective protection, depending on the method of implementation, are divided into construction-acoustic, architectural-planning and organizational-technical and include:
changing the direction of noise emission;
rational planning of enterprises and production premises;
acoustic treatment of the room;
application of sound insulation.
Rational planning of enterprises and industrial premises makes it possible to reduce the noise level in the workplace by increasing the distance to noise sources.
When planning the territory of enterprises, the noisiest premises should be concentrated in one or two places. The distance between noisy and quiet rooms should provide the necessary noise reduction.
If the enterprise is located within the city, then noisy premises should be located deep within the enterprise territory, as far as possible from residential buildings. Inside the building, quiet rooms must be located away from noisy ones so that they are separated by several other rooms or by a fence with good sound insulation.
Architectural and planning solutions also include the creation of sanitary protection zones around enterprises. As the distance from the source increases, the noise level decreases. Therefore, creating a sanitary protection zone of the required width is the easiest way to ensure sanitary and hygienic standards around enterprises.
The choice of the width of the sanitary protection zone depends on the installed equipment; for example, the width of the sanitary protection zone around large thermal power plants can be several kilometers. For objects located within the city, the creation of such a sanitary protection zone sometimes becomes an impossible task. The width of the sanitary protection zone can be reduced by reducing noise along the paths of its propagation.
4 Personal protective equipment
Very often, technical and architectural-construction methods of noise reduction require significant material costs and are not economically feasible. At the same time, there are a number of processes and industries where the only means of protecting workers from high-level noise is PPE (anti-noise protection). In most cases, it is possible to reliably protect a person in production conditions only with the help of MSZ from noise - anti-noise devices. However, noise suppressors must provide not only reliable protection, but more or less comfortable and safe conditions for their use.
Requirements for the effectiveness of noise protection are formulated in GOST 12.4.051 “Personal protective equipment. General technical requirements and test methods". In order to formulate the necessary and appropriate requirements for the effectiveness of noise control, it is necessary to know the scale and levels of maximum permissible noise levels in production.
At one time, the Moscow Institute of Occupational Safety and Health carried out work to clarify the generalized requirements for the values of sound attenuation (efficiency) of noise protection devices. For this purpose, an analysis was carried out of the measurement results of noise levels in the octave bands of the most characteristic “noisy” equipment. The analysis covered the results of measurements at enterprises of mechanical engineering, metallurgy, woodworking, textile and light, electromechanical, radio engineering, food industries, as well as at workplaces in the cabins of construction and road machines. In each octave band of the standardized frequency range, the frequency coefficient of excess of standard noise values was calculated.
Two conclusions that are important for practical purposes can be drawn:
- there are almost no cases of exceeding standard values in the band with an average frequency of 63 Hz. Consequently, the requirements for the effectiveness of noise suppressors at this frequency need not be established, which ultimately leads to a significant reduction in the weight and size of the noise suppressors; anti-noise devices should provide protection in the frequency range of 250–8,000 Hz, where Ki values are relatively close and range from 0.61–0.87;
- the maximum frequency coefficient of excess occurs in the range from 500 to 2,000 Hz.
The conclusions made allow us to formulate some qualitative
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