Air in the working area of production
Organization of control over compliance with sanitary standards;
Training of workers on sanitary requirements.
Technological measures include means, methods and methods used to combat harmful production factors: installations for ventilation and heating; lighting and devices; alarm and control devices for harmful substances in industrial premises; devices for air purification from impurities; technical ways of dealing with noise, vibration, radiation, etc.; means of individual and collective protection of workers.
Thus, industrial sanitation includes the solution of the following issues:
1. Basic sanitary requirements for the location of enterprises and the planning of its territory.
2. Sanitary requirements for industrial buildings.
3. Sanitary requirements for household and auxiliary premises.
4. Sanitary requirements for improving the parameters of the microclimate and the composition of the air environment.
5. Requirements for the organization of industrial lighting in the workplace.
6. Noise protection requirements.
7. Vibration protection.
8. Protection against electromagnetic, x-ray, laser, radioactive and thermal radiation.
Working area air
Air condition working area are determined by the microclimate parameters and the composition of the air environment. The microclimate parameters and the composition of the air environment must comply with the requirements of GOST 12.1.005-88 "General sanitary and hygienic requirements for the air of the working area" and DNAOP 0.03-3.15-86 "Sanitary microclimate standards industrial premises No. 4088-86".
The microclimate is understood as a complex physical properties factors of the air environment that affect the thermal state of a person. The microclimate is formed by the following parameters:
Air temperature;
Air humidity;
air speed;
The intensity of infrared radiation.
There are the following types of microclimate:
1. Heating - can lead to overheating of the body (hot shops, foundries, thermal, deep mine workings, etc.).
2. Cooling - can lead to hypothermia of the body (refrigeration shops, construction and installation work in the cold season, etc.).
3. Optimal - with prolonged systematic exposure, it provides a normal thermal state of the body, a feeling of comfort and creates conditions for a high level of performance.
4. Permissible - with prolonged and systematic exposure, it can cause short-lived changes thermal state body, accompanied by uncomfortable thermal sensations that worsen well-being and reduce performance.
5. Maximum permissible - with prolonged and systematic exposure, it can lead to persistent changes in the thermal state of the body, accompanied by a breakdown in the body's thermal stability and complaints of pronounced overheating or hypothermia.
The main role in maintaining the optimal thermal state is assigned to thermoregulation, i.e. processes of heat generation and heat transfer to the external environment, aimed at ensuring the thermal stability of the body, i.e. maintaining internal temperature body at a constant level.
When working in a heating microclimate, sweating (4-8 liters per shift) disrupts water-salt, protein, carbohydrate metabolism, dehydration of the body, loss of trace elements (potassium, calcium, magnesium, zinc, iodine, etc.) and water-soluble vitamins (C, B1, B3). There are changes in the cardiovascular and nervous systems, as well as in the respiratory systems. In workers, the pulse quickens, the maximum arterial pressure rises and the minimum decreases, hypertrophy of the left ventricle of the heart develops. The frequency of respiration increases by 2 - 2.5 times, it becomes superficial. Attention is weakened, reaction slows down, coordination of movements is disturbed, efficiency decreases.
Under the influence of excess heat from outside, increased heat production of the body (especially during heavy physical work) and difficult heat transfer, industrial hyperthermia, or overheating, develops.
Infrared radiation (IR) causes a feeling of heat, burning, pain, increased pulse rate, blood pressure, increases the rate of biochemical reactions. Under the action of IR, conjunctivitis, clouding of the cornea of the eye, skin burns, brown-red pigmentation can develop. From occupational pathology, heat stroke and cataracts should be distinguished.
When working in a cooling microclimate, cooling and hypothermia (hypothermia) of the body can occur. Vascular spasm is observed, accompanied by a sensation of pain, metabolic processes in the body increase, blood pressure increases, changes carbohydrate metabolism. Deep cooling depresses the function of the central nervous system, can lead to cold injury, frostbite of certain parts of the body. Prolonged exposure to a cooling microclimate (especially with moisture) can lead to the development of occupational pathology.
Microclimate standards are given in GOST 12.1.005-88 "General sanitary and hygienic requirements for the air of the working area" and DNAOP 0.03-3.15-86 "Sanitary microclimate standards for industrial premises No. 4088-86".
The optimal and permissible values of temperature, relative humidity and air velocity are determined depending on the period of the year and the category of work. Optimal microclimate indicators apply to the entire working area of the premises (to a height of 2 m from the floor level of the working platform), permissible - to permanent and non-permanent workplaces of the working area. Permissible indicators are established in cases where, according to technological, technical and economic reasons it is impossible to provide optimal standards.
The year is divided into warm and cold periods. The warm period is the period of the year, which is characterized by an average daily temperature of the outside air above + 10 ° C, and the cold period is the period characterized by a temperature equal to or below + 10 ° C. Works on the basis of the total energy consumption of the body are divided into categories.
Light physical work (category I) covers activities in which energy consumption is up to 139 J / s - category Ia and from 140 to 174 J / s - category Ib. Category Ia includes work performed while sitting and not requiring physical stress, category Ib - work performed while sitting, standing or walking and accompanied by some physical stress.
Physical work of moderate severity (category II) covers activities in which energy consumption is from 175 to 232 J / s - category Pa and from 233 to 290 J / s - category IIb. Category H includes work related to walking, moving small (up to 1 kg) products or objects in a standing or sitting position and requiring some physical exertion. Category IIb includes work performed while standing, associated with walking, carrying small (up to 10 kg) weights and accompanied by moderate physical exertion.
4. Air of the working area.
4.1. Causes and nature of pollution.
The air environment in which a person lives and works is a multi-gas mixture that makes up the atmosphere.
atmospheric air contains (in % by volume): nitrogen - 78.08; oxygen - 20.95; argon, neon and other inert gases - 0.93; carbon dioxide– 0.03; other gases - up to 0.01.
However, the air of the working area rarely has such a composition, because. many technological processes are accompanied by the release of harmful substances - vapors, gases, solid and liquid particles that pollute the atmosphere.
According to the definition of GOST - 12.1.007-88 "SSBT, harmful substances. Classification and General requirements safety” are harmful substances that, when in contact with the human body, can cause occupational injuries, occupational diseases or deviations in health.
At railway enterprises transport (locomotive, wagon depots, power supply distances, etc.) there are production processes and technological operations with the release of harmful substances. These include painting, welding, galvanizing, babbitting and other works.
Harmful substances can enter the human body by inhaling air, eating, and also penetrate through skin and mucous membranes. In sanitary and hygienic practice, harmful substances are divided into chemical and industrial dust. According to the degree of impact on the human body, all harmful substances are divided into four classes (GOST.SSBT.12.1.007-88):
1 - extremely dangerous substances (mercury, lead, ozone, phosgene, etc.);
2 - highly dangerous substances (nitrogen oxides, benzene, iodine, manganese, copper, chlorine, etc.);
3 - moderately hazardous substances (acetone, xylene, methyl alcohol, etc.);
4 - low-hazard substances (ammonia, gasoline, turpentine, ethyl alcohol, etc.).
Industrial dust is also a harmful factor. It can have a fibrogenic, irritating and toxic effect on the human body. The damaging effect of industrial dust is largely determined by the particle size (dispersion).
The harmfulness of industrial dust is determined by its ability to cause occupational diseases of the lungs and skin.
The degree of human damage by harmful chemicals and industrial dust depends on their concentration in the air of the working area and the duration of their exposure.
For the prevention of occupational diseases, maximum permissible concentrations (MPC) of harmful substances have been established. MPC of harmful substances in the air of the working area - these are concentrations that, with the established duration of the working week (h) during the entire working experience, cannot cause diseases or deviations in the state of health.
The current MPCs for harmful substances and dust in the working area are given in GOST 12.1.005-88. It contains MPCs for almost 800 toxic substances. For example, for lead - 0.01 mg / m 3, chlorine - 1 mg / m 3, gasoline - 100 mg / m 3, etc.
4.2. Industrial ventilation.
Industrial ventilation is used in various technological processes and to ensure the meteorological parameters (temperature, humidity) established by sanitary standards and the purity of the air in the room.
Ventilation devices create an air environment at enterprises, in office and work premises, which must comply with labor hygiene standards (GOST.SSBT.12.1.005-88 - General sanitary and hygienic requirements for the air of the working area).
Ventilation provides air exchange in the room, i.e. removes polluted and supplies fresh air.
According to the method of moving air, natural and artificial (mechanical) ventilation are distinguished. natural ventilation - air exchange in the room is carried out due to thermal and wind pressure. At mechanical ventilation air exchange is carried out by fans (centrifugal or axial) with an electric drive.
Ventilation is supply, exhaust and supply and exhaust. According to the place of action, ventilation is divided into general and local.
General exchange - designed to provide air supply to the working area, corresponding to sanitary standards.
local- to remove harmful substances directly from the place of release, in order to prevent them from spreading to all rooms.
In large workshops with local emissions of harmful substances, local suctions are used to remove explosive and flammable gases and vapors. They are designed individually for each room and each working unit. Air heaters are used to heat the air, and filters are used to clean the air.
Fig. 4.1. Schemes of mechanical ventilation.
a) supply
b) exhaust
1-air intakes, 2-air duct, 3-filters, 4-heaters, 5-fan, 6-supply devices, 7-air intake device, 8-air purification device,
9-mine for the emission of polluted air.
Natural ventilation is used to ensure favorable working conditions in rooms where significant heat is generated and special air preparation and supply to certain places is not required.
Air exchange occurs due to the difference in air density inside and outside the room, which is determined by the temperature difference. This causes cold air to enter the room and warm air to be forced out of it (thermal pressure).
Under the action of wind (wind pressure), a reduced pressure is created on the windward side of the building, as a result of which warm air is extracted from the room. On the windward side of the building, on the contrary, pressure is created and fresh air enters the room. (Fig.6.2.)
Natural ventilation of industrial premises can be unorganized (infiltration) and organized (aeration). With unorganized ventilation, air enters the room and is removed from it through loose connections in external fences, windows, vents and other leaks that work for supply and exhaust.
Organized ventilation is carried out in the presence of lanterns with opening sashes, transoms through which air is extracted, and windows or special openings in the side walls that work for inflow.
4.3. Calculation ventilation system
To design a ventilation system for each room, the following steps must be performed:
Determine the required air exchange;
Draw up a basic ventilation system for the room, and aerodynamic calculation of air ducts:
Choose a fan and determine the required power of the electric motor.
Air exchange calculation.
Required air exchange L for general ventilation is determined by the following formulas:
For gas emissions:
Where: L g - the amount of air required to remove excess gases, m 3 / h;
G d – gas release in the room, mg/h;
b d - the maximum permissible concentration of gas in the room, mg / m 3;
b n is the gas content in the supply air.
For moisture release:
In rooms with excessive humidity required amount air L c to remove excess moisture, m 3 / h;
Where: W- the amount of moisture released in the room, mg / h;
γ is the average absolute humidity at normal atmospheric pressure and the arithmetic average temperature of the removed and supply air, mg/m 3 ;
d beats, d inc – relative humidity removed and supply air, %.
For heat dissipation:
Where: Q izb - heat release in the room, kJ / h;
With is the specific heat capacity of air, J/kg. TO;
t beats, t pr– temperature of the removed and supply air, K;
R- air density, kg / m 3.
The amount of air required for ventilation of administrative, residential, public and amenity premises is determined by the air exchange rate:
Where k- the coefficient of multiplicity of air exchange, depending on the purpose of the room and showing how much air should be replaced in the room within an hour;
V n is the volume of the room, m 3.
Natural ventilation can provide 20-fold air exchange, and mechanical - 10-fold.
4.4. Air and air-thermal curtains.
To prevent cold air from entering the premises (shops for the repair of locomotives, wagons, etc.), a air and air-thermal curtains in the form of an air duct with a relatively narrow slot.
The principle of operation of the air curtains is that the air supplied at a certain angle to the plane of the gate prevents the entry of cold outside air into the room. When air is supplied without heating, the curtain is called air, and with heating - air-thermal. Depending on the location of the air ducts with a slot, in relation to the perimeter of the gate, there are lower and side curtains, one-sided and two-sided (Fig. 4.3).
Lower curtains are more economical and more efficient than side curtains, but more difficult to operate, because. often clogged. In locomotive and car depots, two-sided side curtains are usually used with air distribution through rectangular slots of constant width and variable height.
The angle of air outlet from the gap for gates protected from the wind is taken equal to 45 °, for unprotected - 30 °. Air supply speed up to 15 m/s.
Improvement of the air environment and normalization of microclimate parameters
The air environment of the working area.
One of the necessary conditions for healthy and highly productive work is to ensure clean air and normal meteorological conditions in working area premises, i.e. space up to 2 m above the floor level or the platform where the workplaces are located.
Causes and nature of air pollution in the working area
Atmospheric air in its composition contains (% by volume): nitrogen - 78.08; oxygen - 20.95; argon, neon and other inert gases - 0.93; carbon dioxide - 0.03; other gases - 0.01. The air of this composition is the most favorable for breathing. The air of the working area rarely has the above chemical composition, since many technological processes are accompanied by the release of harmful substances into the air of industrial premises - vapors, gases, solid and liquid particles. Vapors and gases form mixtures with air, and solid and liquid particles of a substance - dispersed systems - aerosols, which are divided into dust (solid particle size more than 1 micron), smoke (less than 1 micron) and fog (liquid particle size less than 10 microns). Dust is coarse (particle size more than 50 microns), medium (50 - 10 microns) and fine (less than 10 microns).
The entry into the air of the working area of one or another harmful substance depends on the technological process, the raw materials used, as well as on intermediate and final products. So, vapors are released as a result of the use of various liquid substances, for example, solvents, a number of acids, gasoline, mercury, etc., and gases - most often during the technological process, for example, during welding, casting, heat treatment of metals.
The reasons for the release of dust in mechanical engineering enterprises can be very diverse. Dust is generated during crushing and grinding, transportation of crushed material, machining of brittle materials, surface finishing (grinding, polishing), packaging and packaging, etc. These causes of dust formation are the main or primary ones. Under production conditions, secondary dust formation may also occur, for example, during cleaning of premises, people moving, etc. Such dust emission is sometimes very undesirable (in the electrovacuum industry, instrument making).
Smoke arises from the combustion of fuel in furnaces and power plants, and fog - from the use of cutting fluids, in electroplating and pickling shops in the processing of metals. For example, in the charging compartments of batteries, an aerosol of sulfuric acid is formed.
Harmful substances enter the human body mainly through the respiratory tract, as well as through the skin and with food. Most of these substances are classified as dangerous and harmful production factors, since they have a toxic effect on the human body. These substances, being well soluble in biological media, are able to interact with them, causing disruption of normal life. As a result of their action, a person develops a painful condition - poisoning, the danger of which depends on the duration of exposure, concentration q(mg / m 3) and the type of substance. According to the nature of the impact on the human body, harmful substances are divided into:
general toxic- causing poisoning of the whole organism (carbon monoxide, cyanide compounds, lead, mercury, benzene, arsenic and its compounds, etc.);
annoying- causing irritation of the respiratory tract and mucous membranes (chlorine, ammonia, sulfur dioxide, hydrogen fluoride, nitrogen oxides, ozone, acetone, etc.);
sensitizing- acting as allergens (formaldehyde, various solvents and varnishes based on nitro - and nitroso compounds, etc.);
carcinogenic- causing cancer (nickel and its compounds, amines, chromium oxides, asbestos, etc.);
mutagenic- leading to a change in hereditary information (lead, manganese, radioactive substances, etc.);
affecting reproductive(childbearing) function (mercury, lead, manganese, styrene, radioactive substances, etc.).
Regulation of the content of harmful substances in the air of the working area
According to GOST 12.1.005 - 76, maximum permissible concentrations of harmful substances are established q MPC (mg / m 3) in the air of the working area of industrial premises. Harmful substances according to the degree of impact on the human body are divided into the following classes: 1st - extremely dangerous, 2nd - highly dangerous, 3rd - moderately dangerous, 4th - low-dangerous. As an example, in Table. 1 shows the normative data for a number of substances (in total, more than 700 substances are standardized).
Table 1.
Values of admissible concentrations of substances.
|
Substance |
MPC value, mg / m 3 |
Hazard Class |
State of aggregation |
|
Beryllium and its compounds |
aerosol |
||
|
aerosol |
|||
|
Manganese |
aerosol |
||
|
vapors and (or) gases |
|||
|
vapors and (or) gases |
|||
|
hydrochloric acid |
vapors and (or) gases |
||
|
aerosol |
|||
|
iron oxide |
aerosol |
||
|
Carbon monoxide, ammonia |
vapors and (or) gases |
||
|
Fuel gasoline |
vapors and (or) gases |
||
|
vapors and (or) gases |
Meteorological conditions and their regulation in industrial premises
Meteorological conditions, or microclimate, in production conditions are determined by the following parameters:
air temperature t(°C);
relative humidity (%);
air velocity in the workplace V(m/s).
In addition to these parameters, which are the main ones, one should not forget about atmospheric pressure. R, which affects the partial pressure of the main components of air (oxygen and nitrogen), and, consequently, the breathing process.
Human life can take place in a fairly wide range of pressures 734 - 1267 hPa (550 - 950 mm Hg). However, here it is necessary to take into account that a rapid change in pressure is dangerous for human health, and not the value of this pressure itself. For example, a rapid decrease in pressure of just a few hectopascals in relation to the normal value of 1013 hPa (760 mmHg) causes a painful sensation.
The need to take into account the main parameters of the microclimate can be explained based on the consideration of the heat balance between the human body and the environment of industrial premises.
The amount of heat release Q by the human body depends on the degree of physical stress in certain meteorological conditions and ranges from 85 (at rest) to 500 J / s (hard work).
The release of heat from the human body environment occurs as a result of heat conduction through clothing Q T , convection at the body Q To, radiation to surrounding surfaces Q And, evaporation of moisture from the surface of the skin Q Spanish. Part of the heat is spent on heating the inhaled air Q V .
Normal thermal well-being (comfortable conditions), corresponding to this type of work, is ensured subject to heat balance :
Q=Q T +Q To +Q And +Q Spanish +Q V ,
therefore, the temperature of the internal organs of a person remains constant (about 36.6 ° C). This ability of the human body to maintain a constant temperature when the parameters of the microclimate change and when performing work of varying severity is called thermoregulation.
At high air temperature in the room, the blood vessels of the skin expand, while there is an increased flow of blood to the surface of the body, and heat transfer to the environment increases significantly. However, at ambient air temperatures and surfaces of equipment and premises of 30 - 35 ° C, heat transfer by convection and radiation basically stops. With more high temperature air, most of the heat is given off by evaporation from the surface of the skin. Under these conditions, the body loses a certain amount of moisture, and with it salts, which play an important role in the life of the body. Therefore, in hot shops, workers are given salted water.
When the ambient temperature drops, the reaction of the human body is different: the blood vessels of the skin narrow, the blood flow to the surface of the body slows down, and the release of heat by convection and radiation decreases. Thus, for the thermal well-being of a person, a certain combination of temperature, relative humidity and air velocity in the working area is important.
Air humidity has a great influence on the thermoregulation of the body. High humidity (φ>85%) makes thermoregulation difficult due to reduced evaporation of sweat, and too low humidity (φ<20%) вызывает пересыхание слизистых оболочек дыхательных путей. Оптимальные величины относительной влажности составляют 40 - 60%.
The movement of air in rooms is an important factor influencing the thermal well-being of a person. In a hot room, air movement increases the body's heat transfer and improves its condition, but it has an adverse effect at low air temperatures during the cold season.
The minimum air velocity felt by a person is 0.2 m/s. In winter, the air velocity should not exceed 0.2 - 0.5 m/s, and in summer - 0.2 - 1.0 m/s. In hot shops, it is allowed to increase the blowing speed of workers (air showering) up to 3.5 m/s.
In accordance with GOST 12.1.005 - 76, optimal and permissible meteorological conditions are established for the working area of the premises, the choice of which takes into account:
1) season - cold and transitional periods with an average daily outdoor temperature below +10 ° C; warm period with a temperature of +10°C and above;
A) light physical work with energy consumption up to 172 J / s (150 kcal / h), which include, for example, the main processes of precision instrumentation and mechanical engineering;
b) physical work of moderate severity with energy consumption of 172 - 293 J / s (150 - 250 kcal / h), for example, in mechanical assembly, mechanized foundries, rolling, thermal shops, etc .;
V) heavy physical work with energy consumption of more than 293 J / s, which includes work associated with systematic physical stress and the transfer of significant (more than 10 kg) weights; these are blacksmith shops with hand forging, foundries with hand stuffing and filling of flasks, etc.;
3) characteristics of the premises in terms of excess sensible heat: all production premises are divided into premises with insignificant excesses of sensible heat per 1 m 3 of the volume of the room, 23.2 J / (m 3 s) or less, and with significant excesses - more than 23, 2 J / (m 3 s).
Sheer warmth - heat entering the working room from equipment, heating devices, heated materials, people and other sources, as a result of insolation and affecting the air temperature in this room.
Measures to improve the air environment
The required state of the air in the working area can be ensured by the implementation of certain measures, the main of which include:
1. Mechanization and automation of production processes, their remote control. These measures are of great importance for protection against the effects of harmful substances, thermal radiation, especially when performing heavy work. Automating processes that release harmful substances not only increases productivity, but also improves working conditions, as workers are removed from the hazardous area. For example, the introduction of automatic welding with remote control instead of manual welding makes it possible to dramatically improve the working conditions of the welder, the use of robotic manipulators makes it possible to eliminate heavy manual labor.
2. The use of technological processes and equipment that exclude the formation of harmful substances or their entry into the working area. When designing new technological processes and equipment, it is necessary to achieve the exclusion or sharp reduction in the release of harmful substances into the air of industrial premises. This can be achieved, for example, by replacing toxic substances with non-toxic ones, by switching from solid and liquid fuels to gaseous ones, by electric high-frequency heating; application of dust suppression with water (humidification, wet grinding) when grinding and transporting materials, etc.
Reliable sealing of equipment containing harmful substances, in particular, heating furnaces, gas pipelines, pumps, compressors, conveyors, etc., is of great importance for the improvement of the air environment. gas pressure. The amount of escaping gas depends on its physical properties, the area of leaks and the pressure difference outside and inside the equipment.
3. Protection from sources of thermal radiation. This is important to reduce the air temperature in the room and the thermal exposure of workers.
4. The device of ventilation and heating, which is of great importance for the improvement of the air environment in industrial premises.
5. Use of personal protective equipment.
Ventilation as a means of protecting the air environment of industrial premises
The task of ventilation is to ensure the purity of the air and the specified meteorological conditions in industrial premises. Ventilation is achieved by removing polluted or heated air from a room and supplying fresh air to it.
By way of air movement ventilation happens with natural motivation (natural) and with mechanical (mechanical). A combination of natural and mechanical ventilation (mixed ventilation) is also possible.
Ventilation can be supply, exhaust or supply and exhaust depending on what the ventilation system is used for , - for supply (inflow) or removal of air from the room and (and) for both at the same time.
By place of action ventilation is general and local.
The action of general ventilation is based on the dilution of polluted, heated, humid room air with fresh air to the maximum allowable standards. This ventilation system is most often used in cases where harmful substances, heat, moisture are released evenly throughout the room. With such ventilation, the necessary parameters of the air environment are maintained throughout the entire volume of the room.
Air exchange in the room can be significantly reduced if harmful substances are trapped at the places of their release. For this purpose, technological equipment, which is a source of emission of harmful substances, is equipped with special devices from which polluted air is sucked out. Such ventilation is called local exhaust.
Local ventilation in comparison with general exchange requires significantly lower costs for installation and operation.
In industrial premises in which a sudden entry into the air of the working area of large quantities of harmful vapors and gases is possible, along with the working one, an emergency ventilation device is provided.
In production, combined ventilation systems are often arranged (general exchange with local, general exchange with emergency, etc.).
For the effective operation of the ventilation system, it is important that the following technical and sanitary and hygienic requirements are met at the design stage.
1. The amount of supply air must match the amount of air removed (exhaust); the difference between them should be minimal.
In some cases, it is necessary to organize air exchange in such a way that one amount of air is necessarily greater than another. For example, when designing ventilation of two adjacent rooms, one of which emits harmful substances. The amount of air removed from this room must be greater than the amount of supply air, as a result of which a slight vacuum is created in the room.
Such air exchange schemes are possible when the pressure in the entire room is maintained in excess of atmospheric pressure. For example, in the workshops of electrovacuum production, for which the absence of dust is especially important.
2. Supply and exhaust systems in the room must be correctly placed. Fresh air must be supplied to those parts of the room where the amount of harmful substances is minimal, and removed where the emissions are maximum.
The air supply should be carried out, as a rule, in the working area, and the exhaust - from the upper area of the room.
3. The ventilation system should not cause hypothermia or overheating of workers.
4. The ventilation system should not create noise in the workplace that exceeds the maximum permissible levels.
5. The ventilation system must be electrically, fire and explosion-proof, simple in design, reliable in operation and efficient.
natural ventilation
Air exchange during natural ventilation occurs due to the temperature difference between the air in the room and the outside air, as well as as a result of the action of the wind.
Natural ventilation can be unorganized and organized.
At unorganized ventilation air is supplied and removed through leaks and pores of external fences (infiltration), through windows, vents, special openings (ventilation).
Organized natural ventilation carried out by aeration and deflectors, and can be adjusted.
Aeration. It is carried out in cold shops due to wind pressure, and in hot shops due to the joint and separate action of gravitational and wind pressures. In summer, fresh air enters the room through the lower openings located at a low height from the floor (1-1.5 m), and is removed through openings in the building's skylight.
The intake of outside air in winter is carried out through openings located at a height of 4-7 m from the floor. The height is taken in such a way that the cold outside air, descending to the working area, has time to warm up sufficiently due to mixing with the warm air of the room. By changing the position of the flaps, you can adjust the air exchange.
When buildings are blown with wind from the windward side, an increased air pressure is created, and on the leeward side, a rarefaction is created.
Under the air pressure from the windward side, the outside air will enter through the lower openings and, spreading in the lower part of the building, will displace the more heated and polluted air through the openings in the building skylight to the outside. Thus, the action of the wind enhances air exchange, which occurs due to gravitational pressure.
The advantage of aeration is that large volumes of air are brought in and removed without the use of fans or ducts. An aeration system is much cheaper than mechanical ventilation systems.
Disadvantages: in the summer, the efficiency of aeration is reduced due to an increase in the outdoor temperature; the air entering the room is not processed (not cleaned, not cooled).
Ventilation with deflectors. Deflectors are special nozzles installed on exhaust ducts and using wind energy. Deflectors are used to remove polluted or overheated air from rooms of a relatively small volume, as well as for local ventilation, for example, for extracting hot gases from forges, furnaces, etc.
At present, the TsAGI deflector is most widely used (Fig. 12).
Rice. 12. TsAGI deflector.
1 - diffuser, 2 - cylindrical shell, 3 - cap, 4 - cone, 5 - nozzle
The wind, blowing the deflector shell, creates a rarefaction over most of its circumference, as a result of which the air from the room moves through the air duct and pipe 5 and then goes out through two annular slots between the shell 2 and the edges of the cap 3 and cone 4. The efficiency of the deflectors depends mainly on wind speed, as well as the height of their installation above the roof ridge.
mechanical ventilation
In mechanical ventilation systems, the movement of air is carried out by fans and, in some cases, ejectors.
Forced ventilation. Supply ventilation installations usually consist of the following elements (Fig. 13, A): air intake device 1 for intake of clean air; air ducts 2 through which air is supplied to the room; filters 3 for air purification from dust; heaters 4 for air heating; fan 5; supply nozzles 6; control devices that are installed in the air intake and on the branches of the air ducts.
Exhaust ventilation. Exhaust ventilation installations include (Fig. 8, b): exhaust holes or nozzles 7; fan 5; air ducts 2; device for air purification from dust and gases 8; air ejection device 9, which should be located 1-1.5 m above the roof ridge.
Rice. 13. Mechanical ventilation:
A) - supply; b) - exhaust; V) - supply and exhaust.
During the operation of the exhaust system, clean air enters the room through leaks in the building envelope. In some cases, this circumstance is a serious drawback of this ventilation system, since an unorganized influx of cold air (drafts) can cause colds.
Supply and exhaust ventilation. In this system, air is supplied to the room by supply ventilation, and removed by exhaust ventilation (Fig. 13, A And b) running at the same time.
Supply and exhaust ventilation with recirculation (Fig. 13, V) is characterized by the fact that the air sucked from room 10 by the exhaust system is partially re-supplied to this room through the supply system connected to the exhaust system by air duct 11. The amount of fresh, secondary and exhaust air is adjusted by valves 12. As a result of using such a system, savings are achieved consumed heat for heating the air in the cold season and for its purification.
For recirculation, it is allowed to use the air of rooms in which there are no emissions of harmful substances or the emitted substances belong to the 4th hazard class, and the concentration of these substances in the air supplied to the room does not exceed 0.3 concentrations of MPC.
local ventilation
Local ventilation is supply and exhaust.
Local supply ventilation serves to create the required air conditions in a limited area of the production facility. Local supply ventilation installations include: air showers and oases, air and air-thermal curtains.
Air shower used in hot shops at workplaces under the influence of a radiant heat flux with an intensity of 350 W / m 2 or more. The air shower represents the air stream directed on a working. The blowing speed is 1-3.5 m/s, depending on the irradiation intensity. The effectiveness of showering units is increased by spraying water in an air stream.
Air oases- this is a part of the production area, which is separated from all sides by light movable partitions and filled with air that is colder and cleaner than the air in the room.
Air and air-thermal curtains arranged to protect people from being chilled by cold air entering through the gate. Curtains are of two types: air curtains with air supply without heating and air-thermal curtains with heating of the supplied air in heaters.
The operation of the curtains is based on the fact that the air supplied to the gate exits through a special air duct with a slot at a certain angle at a high speed (up to 10-15 m/s) towards the incoming cold stream and mixes with it. The resulting mixture of warmer air enters the workplaces or (in case of insufficient heating) deviates away from them. During operation of the curtains, additional resistance is created to the passage of cold air through the gate.
Local exhaust ventilation. Its application is based on the capture and removal of harmful substances directly at the source of their formation.
Local exhaust ventilation devices are made in the form of shelters or local suctions.
Shelters with suction are characterized by the fact that the source of harmful secretions is inside them. They can be made as shelters-casings, completely or partially enclosing equipment (fume hoods, display shelters, cabins and chambers). A vacuum is created inside the shelters, as a result of which harmful substances cannot enter the indoor air. This method of preventing the release of harmful substances in the room is called aspiration. Aspiration systems are usually blocked with the triggers of technological equipment so that the suction of harmful substances is carried out not only at the place of their release, but also at the time of formation.
Full shelter of machines and mechanisms that emit harmful substances is the most perfect and effective way to prevent them from entering the indoor air. It is important even at the design stage to develop technological equipment in such a way that such ventilation devices would be organically included in the overall design, without interfering with the technological process and at the same time completely solving sanitary and hygienic problems.
Protective and dedusting covers are installed on machines where the processing of materials is accompanied by dust emission and flying off of large particles that can cause injury. These are grinding, peeling, polishing, grinding machines for metal, woodworking machines, etc.
Fume hoods are widely used in the thermal and galvanic treatment of metals, painting, hanging and packaging of bulk materials, in various operations associated with the release of harmful gases and vapors.
Cabins and chambers are containers of a certain volume, inside which work is carried out related to the release of harmful substances (sandblasting and shot blasting, painting, etc.).
Hoods are used to localize harmful substances rising up, namely during heat and moisture release.
suction panels are used in cases where the use of exhaust hoods is unacceptable due to the condition of the ingress of harmful substances into the respiratory organs of workers. An effective local suction is the Chernoberezhsky panel used in such operations as gas welding, soldering, etc.
