Classification of methods and means of protection against noise. In relation to the protected object, there are methods and means of collective and personal protective equipment.
Means of protection in relation to the source of noise are divided into means that reduce noise along the path of its propagation, and means that reduce noise at the source of occurrence. 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, aerial, hydrodynamic and electrical origin.
Reducing noise along the path of its propagation is possible in the following ways:
Removing the receiver from the source over long distances;
Changing the directivity of the noise source;
Reducing the reverberant sound field with sound absorbing material.
Means and methods of collective protection against noise, depending on the method of implementation, are subdivided into acoustic, architectural and planning, organizational and technical.
Acoustic protection equipment. Protection against noise by acoustic means assumes: sound insulation (construction of soundproof cabins, casings, fences, installation of acoustic screens); sound absorption (use of sound-absorbing facings, piece absorbers); noise mufflers (absorption, reactive, combined).
Soundproofing. A sound wave, possessing a certain energy, collides with an obstacle (fence). In a collision, part of the sound energy is absorbed in the material of the obstacle, some is reflected, and some passes through the obstacle. The equation for the balance of sound energy can be written as
where I PAD is the intensity of the incident sound, W / m 2;
I POGL - the intensity of the absorbed sound, W / m 2;
I ОХР - intensity of reflected sound, W / m 2;
I PRESH - intensity of the transmitted sound, W / m 2.
The passed energy causes the formation of a new sound field on the other side of the obstacle by converting the sound energy into mechanical energy of the obstacle vibrations.
The vibration amplitude of the obstacle is inversely proportional to its mass. Consequently, the amplitude of the oscillations of sound waves in the receiving room is inversely proportional to the mass of the obstacle.
The absorbed energy is converted into another type of energy (usually heat). Soundproofing means are shown in Fig. 6.1.
Rice. 6.1. Typical methods of dealing with noise: 1 - headphones; 2 - soundproofing fence;
3 - screen; 4 - increase in distance; 5 - sound-absorbing ceiling; 6 - soundproof partition; 7 - vibration isolating support
Sound insulation of the fence when a sound wave falls on it is determined from the expression
The sound insulating qualities of flat barriers without holes are determined by the mass of the barrier area unit. A slab consisting of a system of unconnected infinite masses is taken as a design model. Then the sound insulation is subject to the law of masses
(6.16)
where m is the mass of one square meter of the fence, kg (density, kg / m 2);
f - vibration frequency, Hz.
The selected fence meets the requirements of the standards, if in all octave frequency bands the sound insulation value R A is not less than the required values R TPi Sound insulation is determined by the following indicators: mass, uniformity, stiffness, air gap, side noise transmission, frequency.
Sound insulation by a fence with additional indirect transmission of noise (through holes, cracks, pipelines, etc.) is called the actual sound insulation by the fence R f, dB. It is defined as
(6.17)
where S OGR is the area of the fence, m 2;
S O - area of holes in the fence, m 2;
Acoustic screens are used when the SPL of direct sound at the design point is much higher than the SPL of the reflected sound and when the SPL at the design point exceeds the SPL extra by at least 10 dB and no more than 20 dB (Fig. 6.2).
The acoustic effect of the screen is based on the formation of a shadow area behind it, where sound waves only partially penetrate. Screens should be used for sources with a predominantly mid- and high-frequency noise spectrum, since the degree of penetration of sound waves into the acoustic shadow region behind the screen depends on the ratio of the screen dimensions to the wavelength of the incident sound. The larger the ratio of wavelength to screen size, the smaller the area of sound shadow behind it.
Rice. 6.2. Acoustic shielding:
1 - noise source; 2 - high-frequency region; 3 - mid-frequency region; 4 - low-frequency region; 5 - acoustic shadow
The screens are efficiently used in an acoustically treated room or in an open space.
Screens are made of steel or duralumin sheets with a thickness of 1.5-2.0 mm or shields lined with sound-absorbing material with a thickness of at least 50-60 mm. The linear dimensions of the screen must be at least three times the linear dimensions of the noise source.
The screen efficiency ΔL is determined by the formula
(6.20)
where R eq is the sound pressure at a point in the presence of a screen, Pa; R BE — sound pressure at a point without using a screen, Pa. Sound absorption. Sound absorption is understood as the property of acoustically treated surfaces to reduce the intensity of the waves reflected by them due to the conversion of sound energy into thermal energy as a result of viscous friction in the capillaries of the pores and irreversible losses during deformation of the elastic skeleton of the structure. Facing the room with sound absorbers shown in Fig. 6.3 will absorb approximately 70% of the energy of the low frequency noise and 95% of the high frequency noise.
Sound absorbing cladding by the type of sound-absorbing material used, they have the following designs: lining made of rigid homogeneous porous materials; liners with perforated coating in protective sheaths of fabric and film. Mineral wool slabs, canvases made of super-thin fiberglass, mats made of super-thin basalt fiber, foamed polymeric materials and combined materials are used as porous materials. These materials can also be used for thermal insulation at the same time.
Sound-absorbing linings are used when the required decrease in SPL (ΔL TP) at the design point exceeds 1-3 dB in at least three octave bands or exceeds 5 dB in at least one of the octave bands.
It is known from practice that in order to achieve an effect in reducing noise, the area of acoustic finishing of the surface of a room must be at least 60%. The claddings are placed on the walls in the upper quarter of the area. Claddings should be located closer to sources of noise, as well as in places where sound energy is concentrated when it is reflected. Placing the facing slabs in a checkerboard pattern increases their acoustic efficiency by 25-30% in a wide frequency range compared to a solid array.
Silencers... Silencers are used to reduce airborne noise generated by ventilation and air conditioning systems.
Depending on the principle of operation, mufflers are divided into absorption, reactive and combined.
Noise reduction in absorption mufflers occurs due to the absorption of sound energy by the sound-absorbing materials used in them. They work effectively in a wide frequency range when the sound absorption coefficient of the material used is close to unity.
TO absorption silencers include tubular(round and rectangular sections), lamellar, triangular-prismatic, cylindrical.
Tubular mufflers used in channels with a cross section of up to 500-600 mm. The length of the muffler is no more than 1-2 m. Tubular mufflers are made of perforated sheet material, lined with a layer of sound-absorbing material such as super-thin glass fiber. The perforation diameter is d = 4 ... 8 mm, and the pitch is t = 2d.
To reduce the dimensions of the mufflers and increase the noise attenuation per unit length of the wide channel, plate mufflers are used, which is a set of parallel-mounted sound-absorbing plates. Plates are usually made in the form of shields with outer perforated walls, inside of which there is a layer of soft sound-absorbing material with a protective shell made of fiberglass, as well as in the form of partition plates made of solid sound-absorbing materials. The level of noise reduction with plate silencers depends on the thickness of the plates and the distance between them.
Reactive mufflers. These include chamber, resonance and screen mufflers. Chamber silencers consist of one or more chambers, which are cavities in the form of an expansion of the air duct section. In a chamber muffler, sound waves are reflected from the opposite wall and, returning to the beginning in antiphase with respect to the direct wave, reduce its intensity. If the inner part of the expansion of the duct is lined with sound-absorbing material, then you get a combined silencer. The resonant muffler is a cavity of volume V connected to the air duct by a hole called the throat of the resonance chamber. The cavity and the hole form a system that provides almost complete reflection of sound energy back to the source at frequencies close to its natural frequency. Screen mufflers are installed at the exit from the channel to the atmosphere or at the entrance to the channel. They are effective at high frequencies and reduce noise by 10-25 dB.
Combined mufflers - screen, chamber, with sound-absorbing coating.
To reduce noise in ventilation and air conditioning systems resulting from vibration of the walls of air ducts, the latter are covered with vibration-absorbing coatings (mastics). The thickness of the vibration-absorbing material layer must be six times the thickness of the duct wall. At the same time, the efficiency of its application is 5-7 dB, the amplitude of resonant oscillations decreases by about 15 dB.
Architectural and planning methods of collective protection against noise presuppose: rational placement of technological equipment, machines and mechanisms, workplaces in buildings; planning of traffic zones; creation of noise-proof zones in places where a person is located.
Noise is one of the side phenomena harmful to humans that accompanies the production process. In some cases, it can be a hazardous working condition.
These include, for example, working electrical installations and engines, work with firearms.
The Gosstroy decree “On the adoption of SNiP RF“ Labor safety in construction ”recommends the employer to provide the employee with personal hearing protection if the noise level exceeds 80 dB. It should be noted that PPE is issued if collective funds do not help... In this article we will tell you what methods, methods and means of protection against noise exist.
As means of personal protection for hearing organs from noise and vibration are used headphones, earbuds, helmets, suits.
The earbuds close the ear canal... Helmets protect against very high frequency noise that can penetrate the bones of the skull, not just the ear canal.
Headphones reduce negative impact in the range from 7 to 38 dB with a frequency from 125 to 8000 Hz.
The inserts are disposable and reusable. Disposable are made of fine fiber. Can be dry and soaked in wax and paraffin. Reusable made of ebonite, plasticine or rubber, can be cleaned with any detergent.
They are very convenient in rooms with high pollution.
The way of using the earbuds is simple: They are inserted into the ear canal and reduce the harmful effects on the eardrum. It is possible to produce products with a bow, like glasses, or with a drawstring for use in short-term situations.
This type is cheap, compact, applicable to many situations, but not always effective, because reduces the level of negative impact by only 5 - 20 dB. Users report inconvenience in the form of irritation in the ear canal if the earmolds are made of a hard material.
Headphones - PPE is always reusable... These are devices in the form of two bowls, which are connected by a headband. The headband is made of metal or plastic. The inside of the bowl is filled with noise-reducing foam.
Release with active, passive and communication protection as well as communication headsets.
Passive assumes only the protection of the ear canal from the effects of noise, for example, headphones with suppression of external noise for shooting at a shooting range. All sounds in this case become quieter.
Active allows you to resist a negative factor, for example, in industrial production.
The general principle of active protection is as follows: The speakers pick up sounds, dampen them, and the microphones allow you to communicate. The communication protection is provided by a radio station or a mobile phone. For high-quality communication under heavy loads, the user can connect a walkie-talkie, telephone and other means of communication.
Communication headsets equipped with a comprehensive system of protection and communication. The higher the frequency of the negative sound, the greater the need to use headphones.
If the noise level in the manufacturing process is high enough, the headphones and earbuds will not cope with the load. In industry, processes accompanied by ultrasound are frequent, for example, in metallurgy, mechanical engineering, metal processing.
According to sanitary standards, the ultrasound level should not exceed 110 dB.
Ultrasound power can reach tens of kilowatts... Its danger lies in the impact on a person through air, liquid, any solid media. A helmet or noise protection suit can help to cope with this. The suit consists of a helmet and a vest, on which additional noise-absorbing layers of fabric are applied.
The choice of a product is determined by several factors: production specifics, environment, required protection quality, various noise categories.
Such factors include, for example, sharp single sounds or constant monotonous noise of high tones; humid or dry room air, etc.
How effective is the type of protection determines the SNR - reduction of sound noise... This value is indicated by the manufacturer on all PPE or on packages. Do not forget that the selection of a product should be based on specific conditions, because the increased SNR can drown out the signals needed in a working situation.
For a quality choice, you need to proceed from the following indicators:
- The better the material for the earbuds, the more convenient they are to use and the longer they can be used in one session.
- The larger the diaphragm of the headphones, the better the sound quality.
- The greater the sensitivity of the headphones, the higher their efficiency. Average indicator - 100 dB... The headphone power determines the sound volume. The level of distortion is expressed as a percentage. Distortion of 1% is accepted as normal if the noise exceeds 100 Hz... If the noise level is lower, distortion can be 10%... All characteristics are indicated on the product packaging.
It must be remembered that when carrying out certification, headphones are subjected to laboratory tests, which are almost 2 times different from real conditions.
If you would like to know in more detail what applies to electrical protective equipment, we will tell you in this one.
Storage, delivery and care rules
An employer in production, when providing workers with personal protective equipment, for example, protective ear muffs, must instruct them on the rules for their use.
To store inventory, there must be dedicated premises and must be issued by a certain person.
Their number should be sufficient for all employees, and one-time funds should be issued daily or as needed.
Taking PPE outside of professional use is prohibited. if it is not stipulated by the Employment Agreement.
As for all reusable personal hygiene items, for protective equipment should be looked after... Headphones and helmets should be washed or wiped down after each working day or as needed. The reusable earbuds need to be rinsed off dirt and earwax.
Today, there are enough personal hearing protection equipment, from the simplest to the modern electronic ones. Their choice should depend on the level of negative impact so that the production process does not suffer.
We bring to your attention a small video review about active headphones:
Topics: Safety in welding.
Noise protection are subdivided into collective and individual (PPE). Of the former, sound insulation, sound absorption and noise mufflers are most often used.
The means of protection against noise are developed or selected on the basis of an acoustic calculation, which makes it possible to determine at the design stage the expected sound pressure levels (SPL) at design points with known noise sources (IS) and their noise characteristics, or noise measurements (in operating conditions). Required noise reduction, dB, Mtr = L - Ldop, where L - calculated or measured SPL; Ldop - permissible SPL. The acoustic calculation technique is known from the literature.
1) Soundproofing means. Soundproofing means (see Figure 1) include: 1 - soundproofing fences, 2 - soundproofing cabins and control panels, 3 - soundproofing casings, 4 - acoustic screens. They are used when it is necessary to significantly reduce the intensity of direct sound at workplaces.
Soundproof fences(walls, ceilings, windows, etc.) are characterized by sound insulation R (dB) of airborne noise. The required sound insulation Rtp (dB) of the fencing of adjacent rooms is determined as Rtp = Lw - L add + 10 lg S ogp - 10 Ig V and, where Lw is the measured or calculated SPL in a noisy room; L add - permissible SPL in the insulated room, dB; B and - the constant of the insulated room (m 2), determined by reference data; Sorp - fencing area, m 2.
Calculation and design of soundproof fences is carried out taking into account R tr. There are two possible ways to solve this problem: 1) the use of experimental data on sound insulation of fences R ogp ≥ R tr at standard geometric mean frequencies of octave bands; 2) calculated in accordance with SNiP II-12-77 definition R.
Rice. 1. Soundproofing means.
For approximate calculations of a single-layer fence, use the formula
R = 20 lg mƒ- 47.5,
where m is the surface density of the fence material, kg / m 2 (t = ρh, where ρ is the density of the material, kg / m 3; h is the thickness of the fence, m); ƒ - sound frequency, Hz.
Soundproof enclosures made of steel, duralumin and other materials. The inner surface of the casing walls must be lined with sound-absorbing material (SPS). For a continuous sealed casing, its required sound insulation R.ozh.tr = L - Ladd is provided due to the sound insulation of the casing walls (dB):
R = R leather tr - 10 lg α region,
where α obl is the reverberation coefficient of sound absorption of the used ZPM (Table 18.13).
Calculation of soundproofing of enclosures can be found in reference books.
Soundproof cabins are used to place remote controls in them, workplaces in noisy industrial premises.
The required noise reduction by the cabin R cab.tr = L w - L additional, where L w is the octave sound pressure level at the workplace of the cab installation, dB; L additional permissible SPL at workplaces in cabins, dB.
The required sound insulation of the R i -th element of the cabin (wall, window, door) is determined by the formula R TP i = L w -10 lg B k + 10 lg S i - L up + 10 lg n, where B k is the constant of the cabin, m 2; S i - area of the i-th element of the cabin, through which the noise penetrates into the cabin, m 2; n is the number of identical elements, for example windows.
Acoustic screens most often they are made of flat and U-shaped metal sheets with a thickness of 1 ... 2 mm with a mandatory lining with a layer of sound-absorbing material of the surface facing the noise source. The shielding efficiency is the higher, the greater the ratio of the width and height of the screens and the sound wavelength λ = c / ƒ, m (c is the speed of sound in air, c = 340 m / s); therefore, it is advisable to use them to reduce medium- and high-frequency noise ... The method for calculating acoustic baffles has been published.
Rice. 2. Soundproof booth.
2) Noise protection :
Sound absorption means... These are sound-absorbing facings and piece sound absorbers installed in the room during its acoustic treatment. The decrease in SPL in the room for workplaces located in the zone of reflected sound is determined by the formula ΔL = 10 lg, dB, where B and ψ are the room constant and the coefficient before acoustic treatment, respectively; В 1 and ψ 1 - the same after processing. Sound-absorbing claddings are used in the form of acoustic plates "<Акмигран», «Акминит» и др.) и слоев пористоволокнистых материалов (стеклянного или базальтового супертонкого волокна, минеральной ваты и др.) в защитной оболочке из стеклоткани типа Э3-100 с перфорированным покрытием (металлическим, гипсовым и др.). Реверберационные коэффициенты звукопоглощения α обл для некоторых конструкций даны в табл. 18.13.
To reduce noise, the workplace of the operator of the thermal cutting installation must be fenced with a soundproof booth-screen, the diagram of which is shown in Fig. 2. The wall of the cabin is made of a solid metal sheet (1) with a thickness of 1.5 ... 2 mm with a sound-absorbing lining 2 with a thickness of 50 mm, located on the outer and inner sides of the cabin and closed with a layer of glass cloth of the E3-400 type and a metal perforated sheet 3 thick from 1 to 1.5 mm (must have a perforation ratio ≥20%). It is also possible to install flat acoustic screens between the workplace and. In this case, the screens should only be used in combination with the sound-absorbing cladding of the production area.
To reduce noise in the workshop, rotating yards and multi-station generators need to be soundproofed or taken out of the workplace or area, room.
3) Noise protection : Noise mufflers. To reduce the noise of fan and compressor installations, plate, tubular, cylindrical absorption silencers are used (Fig. 3). Silencer designs are selected depending on the transverse dimensions of the air ducts, the permissible air flow rate, the required decrease in SPL. Silencers with porous elements are used to reduce the noise of compressed air discharge systems.
Rice. 3. Tubular silencer: J - perforated sheet; 2 - sound-absorbing material; 3 - case.
Reducing noise at the source is achieved by improving the design of machines and the use of low-noise materials in these structures, vibration damping of the noise source, and the use of a special shelter for work.
Reducing noise along the path of its propagation is possible in the following ways:
Removing the receiver from the source over long distances;
Changing the directivity of the noise source;
Reducing the reverberant sound field with sound absorbing material.
Means and methods of collective protection against noise, depending on the method of implementation, are subdivided into acoustic, architectural and planning, organizational and technical.
Acoustic protection equipment. Protection against noise by acoustic means assumes: sound insulation (construction of soundproof cabins, casings, fences, installation of acoustic screens); sound absorption (use of sound-absorbing facings, piece absorbers); noise mufflers (absorption, reactive, combined).
Soundproofing. A sound wave, possessing a certain energy, collides with an obstacle (fence). In a collision, part of the sound energy is absorbed in the material of the obstacle, some is reflected, and some passes through the obstacle.
VIBRATION
The effect of vibration on the human body: General and local vibration is distinguished according to the effect on the human body. General vibration causes a shake of the whole organism, local vibration involves individual parts of the body. Transport workers, operators of powerful dies, cranes, etc. are exposed to general vibration. People working with hand-held electric and pneumatic tools are exposed to local vibration.
With short-term exposure to vibration, the worker gets tired prematurely, and his labor productivity decreases. Long-term exposure to general vibrations, characterized by a high level of vibration velocity, can be the cause of vibration disease? persistent violations of the physiological functions of the body, mainly due to the effect of vibration on the central nervous system (central nervous system of a person). These disorders are manifested in the form of headaches, dizziness, poor sleep and poor health, decreased performance, joint pain, cardiac disorders.
Vibration disease belongs to the group of occupational diseases, the effective treatment of which is possible only in the early stages. Restoration of impaired functions proceeds very slowly, and in especially severe cases, irreversible changes occur in the body, leading to disability
The basis for the hygienic regulation of vibration is the criteria of human health when exposed to vibration, taking into account the intensity and severity of labor. Vibration is divided into dangerous and safe
Sanitary and hygienic vibration rationing regulates the parameters of industrial vibration and the rules for working with vibration-hazardous mechanisms and equipment, GOST 12.1.012-90 “SSBT. Vibration safety. General requirements ", SN 2.2.4 / 2.1.8.566-96" Industrial vibration, vibration in residential and public buildings "
VIBRATION PROTECTION
For vibration protection, vibration-absorbing and vibration-insulating materials and structures are widely used.
Vibration isolation is a decrease in the vibration level of a protected object, achieved by reducing the transmission of vibrations from their source. Vibration isolators are elastic elements located between the vibrating unit and its base. Vibration dampers are made from rubber gaskets and steel springs. Foundations for heavy equipment that cause significant vibrations are made buried and insulated on all sides with cork, felt, slag, asbestos and other vibration-damping materials. To reduce vibration of casings, fences and other parts made of steel sheets, a layer of rubbers, plastics, bitumen, vibration-absorbing mastics is applied to them, which dissipate the vibration energy. In cases where technical and other measures fail to reduce the noise and vibration level to permissible limits, personal protective equipment is used. As individual means of protection against noise in accordance with GOST 12.1.029-80, soft anti-noise inserts are used, inserted into the ears, tampons made of ultra-thin fiber or hard ones made of ebonite or rubber, effective at L = 5-20 dB. At sound pressure L> 120 dB, headphones of the VTsNIIOT type are recommended, designed to protect against high-frequency noise; helmets, hard hats and special anti-noise suits.
To protect hands from the effects of local vibration, according to GOST 12.4.002-74, gloves or gloves of the following types are used: gaskets or plates that are equipped with attachments to the arm (GOST 12.4.046-78). To protect against vibration transmitted to humans through the feet, shoes with thick rubber or felt soles should be used. Rational planning of work and rest is important in vibration protection. The total time of exposure to vibration should not exceed 2/3 of the duration of the work shift. It is necessary to arrange breaks for active recreation, carry out physioprophylactic procedures, industrial gymnastics, etc.
Noise is one of the most widespread harmful phenomena of an industrial nature, and in certain conditions it acts as a dangerous industrial factor. There are several types of noise protection: collective and individual. As for collective funds, they often use:
- soundproofing,
- mufflers and sound absorption.
When developing such tools, the main emphasis is on acoustic calculation, which allows you to determine, even at the design stage, what sound pressure levels will be at design points for certain noise sources, as well as their noise characteristics, or measuring noise under operating conditions.
Types of soundproofing. Description
Soundproofing includes:- soundproof cabins, as well as control panels,
- soundproof fences,
- acoustic screens,
- sound insulating casings.
Sound insulating casings are made of steel, duralumin or other metals. The inner surface of such a casing is lined with sound-absorbing material. In addition, various artificial sound absorbers of various designs are used in the premises, which are suspended from the ceiling. Sound is absorbed due to the conversion of the energy of air particles into heat, which fluctuates due to friction losses in the lining material.
In sound-absorbing cladding, which is used for houses, materials such as glass wool, nylon or mineral wool, acoustic boards with a fibrous or granular structure are used. To make this material effective, open pores must remain on the side of the sound incidence.
Soundproof fences
They are: walls, ceilings, glazed openings, partitions, doors, windows.These funds isolate the room from extraneous sound quite well. Such insulation is obtained by creating airtight barriers against airborne noise. Soundproofing of a partition depends on its thickness, therefore they are made of concrete, metal, brick, reinforced concrete, glass, ceramic blocks.
For noisy mechanisms and machines, soundproof enclosures are acceptable, which are made of construction materials:
- aluminum alloys,
- become,
- plastic.
Soundproofing cabins is a means of noise protection, which is located on automated lines (control growths, in noisy workshops) and is aimed at isolating a person from outgoing noise.
When it is not possible to completely isolate the source of the noise, or the person by means of a fence, then noise reduction is achieved by using acoustic baffles. This is a structure made of solid sheets (plexiglass, plywood, metal), 1.5 - 2 mm thick. Flat screens provide protection only in the range of direct sound, with an initial frequency of 500 Hz. And concave screens of C-shaped, U-shaped and other shapes create the desired effect only in the zone of reflected sound, where the frequency is 250 Hz.
Also, to reduce noise, they use means such as noise mufflers, they are used to reduce aerodynamic noise.
Such mufflers are divided into:
- mufflers of active or absorbing type,
- combined mufflers,
- mufflers of reactive or reflective type.
Personal protective equipment
This category of funds includes:
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