Sources of electromagnetic fields. Electromagnetic fields in the human environment are created by natural and artificial sources. Natural sources are solar and cosmic radiation, magnetic properties Grounds, lightning strikes and others.
Anthropogenic sources of electromagnetic fields are divided into two groups:
1st group - sources generating static electric and magnetic fields, as well as extremely low and ultra-low frequencies, which include all means of generation, transmission and distribution of electricity - power plants, equipment and electrical devices for the transmission, distribution and use of electricity (including power lines of direct and alternating current of industrial frequency - 50 Hz).
2nd group - sources generating electromagnetic fields in the radio frequency range, including microwave - from 300 MHz to 300 GHz (radio and television transmitters, radar stations, telecommunications equipment and related devices, such as mobile phones, stations radio relay and satellite communications, location and navigation systems, televisions, computers and other equipment).
From an environmental and medical point of view, electromagnetic fields can be divided into four main types - electrostatic, permanent magnetic, industrial frequency and radio frequency. The problem of the impact of electrostatic fields on health primarily affects working personnel, but even in a modern home, decorated with synthetic materials, equipped with televisions and personal computers, it is possible to increase the level of electrostatic tension. magnetic field.
The problem of exposure to permanent electromagnetic fields is relevant for workers of nuclear magnetic resonance installations, magnetic separators and other equipment that uses permanent magnets.
The most significant sources of electromagnetic fields are widespread radio, television and radar stations and high-voltage power lines. The operation of these facilities is accompanied by the release of electromagnetic radiation into the environment in a wide frequency range - from 50 Hz to 300 GHz. In Russian cities, the number of transmitters on television center towers located within residential areas is constantly increasing. major cities. In addition, independent radio and television broadcasting stations are appearing, and in some cases the level of intensity of electromagnetic fields around them does not meet sanitary and hygienic requirements. This can significantly complicate the electromagnetic environment in adjacent residential areas. In recent years, sources of electromagnetic fields such as video display terminals and radiotelephones, and mobile communication systems have become widespread.
Hygienic standardization. Frequency electromagnetic field expressed in Hertz (Hz). The main quantitative characteristics of the electromagnetic field in the range from fractions of Hz to 300 MHz are electrical intensityE(V/m) and magnetic intensity #(A/m). In the frequency range from 300 MHz to 300 GHz, the intensity of electromagnetic radiation is estimated by energy flux density, the unit of measurement of which is W/m 2. In the case of low and extremely low frequencies, the unit in tesla (T) is also used, one millionth of which corresponds to 1.25 A/m.
Hygienic regulations for electromagnetic fields were established on the basis of:
Detection, measurement (monitoring) and establishment of basic patterns of their changes in space and time in combination with other factors environment;establishing the nature and extent of their biological effects in experiments on animals and during observation of people;
Standardization of electromagnetic fields of various frequencies, i.e., scientific justification of permissible levels of their expression in the environment" normalization, i.e. development and implementation of technical, technological, planning and other measures to limit electromagnetic exposure of people;
Forecasting the electromagnetic situation for the future.
A long-term study of the biological effects of electromagnetic fields on the health of the population of the USSR led to the creation of the world's first sanitary standards and rules for the placement of radio, television and radar stations. Subsequently, these standards were improved, and currently the main regulatory document of the Russian Federation regulating permissible levels of exposure to electromagnetic fields is Sanitary Norms and Rules SanPiN 2.2.4/2.1.8.055 - 96 “Electromagnetic radiation in the radio frequency range (RF EMF).” In this document, electric field strengths are normalized depending on the frequency range. Maximum limits for magnetic field strengths for the population have not yet been established.
In order to protect the population from the effects of electromagnetic fields, special security zones are established around power lines, in which it is prohibited to place residential buildings, parking lots and stops for all types of transport, or to arrange recreation areas, sports and playgrounds. Protective zones are created around radar stations, antenna fields, and powerful radio transmitters, the size and configuration of which are determined by the parameters of the equipment and the terrain.
Obstacles to improving hygienic standards, according to G.A. Suvorov et al. (1998), are the insufficient knowledge of the biological effects caused by the electromagnetic factor, their dependence on the physical parameters of irradiation, the lack of data on the primary mechanisms of interaction of electromagnetic fields of various frequency ranges with body tissues and on the absorption and distribution of energy in biological media.
In the locations of transmitting radio stations, television centers, repeaters and radars, the intensity of electromagnetic fields, depending on the power of the radio transmitting object and the distance to the antenna, in the short wave range (HF) ranges from 0.5 to 75 V/m, in the ultra short wave range (VHF) ) - from 0.1 to 8 V/m, and in the ultrahigh frequency range (microwave) - from 0.5 to 50 μW/cm 2. The propagation of electromagnetic waves is significantly influenced by the nature of the relief,
covering the surface of the earth, placing large objects on it. In places where transmitting HF radio stations are installed at a distance of 20-800 m from the antenna, the field strength ranges from 0.1-70.0 V/m, and near medium-wave (MV) radio stations - from 5 to 40 V/m -> at a distance of 100 - 1000 m. Under certain conditions, the electrical intensity even at distances of several kilometers can reach tens of V/m. Depending on the operating mode of a particular radio engineering facility, the duration of exposure to the electromagnetic field on the population can be 12 - 20 hours/day or more.
The strength of the electromagnetic field indoors also depends on the orientation of the corresponding building in relation to the radiation source, the material of the building structures, etc. Thus, in a brick house the tension is 5 times lower than in an open space, and in a house made of reinforced concrete panels it is 20 times lower. The highest field strength in the VHF (television) range (0.2 - 6.0 V/m) is observed within a radius of 100-1500 m from transmitting antenna systems, with the maximum observed at a distance of 300 m.
Along with radio engineering objects, significant sources of electromagnetic fields are high-voltage overhead power lines emitting electromagnetic waves of low (industrial) frequency - 50 Hz. The actual electric field strength under power lines can vary widely, reaching 10-14 kV/m in some cases. Grounded metal supports provide a pronounced shielding effect, and therefore, in the immediate vicinity of them, the field strength is reduced by 3 to 5 times. The distribution zone of electromagnetic fields from power lines does not exceed several tens of meters, however, with a large length of lines along them, huge areas with high field strength are created at the surface of the earth.
The standard regulating the level of electrostatic field strength for the population is “Sanitary and hygienic control of polymer building materials intended for use in the construction of residential and public buildings” No. 2158-80, according to which the maximum permissible frequency of electrostatic fields is 15 kV/m. Similar levels of electrostatic field strength are established by the standards of the USA and Western European countries.
Impact on public health. The action of electromagnetic fields manifests itself in a variety of ways and its nature is determined by the frequency of the field. Almost every person in the world is exposed to electromagnetic fields of varying frequencies in the range from 0 to 300 GHz. Electromagnetic fields are risk factors for the development of cardiovascular, neuropsychiatric, cancer and some other diseases. Experimental studies to determine the impact of industrial frequency electromagnetic fields made it possible to identify wide range health problems in animals. More than 20 years ago, their influence on behavior, memory, functions of the blood-brain barrier, conditioned reflex and other types of animal activity was established. Their impact affected the development of animal embryos, and an increase in developmental defects was recorded. The carcinogenic effect of the fields was also studied.
The influence of electromagnetic fields of industrial frequency generated near power lines, substations, transformers, under the contact network railways, on human health has not yet been studied enough. According to some existing hypotheses, they are risk factors for the development of malignant neoplasms, Alzheimer's and Parkinson's diseases, memory impairment and other changes, but the results of epidemiological studies are ambiguous.
In Russia, epidemiological studies of the effects of electromagnetic fields on public health are rare. Retrospective cohort method, the essence of which is long-term tracking of a cohort of individuals living near energy facilities! revealed a statistically significant increase in standardized relative risk.
Staying in the zone of influence of electromagnetic fields can cause certain changes in the health status of children. Depending on the time spent in the radiation zone, they observed deviations in weight, height and circumference chest. Development skeletal systems At first it was somewhat delayed, and then, due to the acceleration of ossification processes, it even outstripped the corresponding ones in the children of the control group. The timing of puberty turned out to be shorter than in the control group, and the content of growth hormone was slightly lower. Tendencies were identified to suppress the acid-forming function of the stomach and reduce the function of the adrenal cortex. According to M.V. Zakharchenko, V.1skitina and V. Lyuty (1998), the detected deviations cannot be considered only as a manifestation of adaptive reactions, they can be evidence of quite profound changes in the body under the influence of microwave fields.
Electromagnetic fields of industrial frequency can have a certain impact on the development of breast tumors, neurodegenerative diseases and neuropsychiatric disorders.
Electromagnetic fields of cellular communications. In recent years, cellular telephone radio communication systems have been intensively developing in Russia, and more than 1 million people. use it. Electromagnetic fields created by mobile communications pose a certain danger to human health, since the source of radiation is close to the user’s head. When using a cell phone, the brain and peripheral receptor units of the vestibular and auditory analyzers, as well as the retina of the eye, are exposed to electromagnetic fields of a certain frequency and modulation with a diffuse depth distribution and the amount of absorbed energy with an indefinite frequency and total duration of exposure. The amount of energy absorbed by the brain when operating a cell phone can fluctuate within a certain range depending on the power of the equipment, carrier frequency and other factors. In various countries around the world, with the involvement of volunteers, studies are being conducted to determine the impact of electromagnetic fields from cell phones on health. There are results indicating the presence of changes in the bioelectrical activity of the brain, a slight decrease in cognitive activity (memory deterioration, concentration), and visual impairment. There are currently no statistically reliable data on the development of possible long-term consequences in cell phone users. IARC has begun conducting a multicenter study to assess the possible development of brain cancer and salivary gland, as well as leukemia in cell phone users in various countries around the world.
The Russian National Committee for Non-Ionizing Radiation Protection adheres to the precautionary concept of limiting telephone communications. Children under 16 years of age are not recommended to use mobile phones. Pregnant women and people suffering from epilepsy, neurasthenia, psychopathy and psychasthenia should limit the duration of one conversation to 3 minutes.
In the process of evolution and life activity, a person is influenced by the natural electromagnetic background, the characteristics of which are used as a source of information that ensures continuous interaction with changing environmental conditions.
However, due to scientific and technological progress, the electromagnetic background of the Earth has now not only increased, but also undergone qualitative changes. Electromagnetic radiation has appeared at wavelengths that are of artificial origin as a result of man-made activities (for example, the millimeter wavelength range, etc.).
The spectral intensity of some man-made sources of electromagnetic field (EMF) may differ significantly from the evolutionarily developed natural electromagnetic background to which humans and other living organisms of the biosphere are accustomed.
Sources of electromagnetic fields
The main sources of EMF of anthropogenic origin include television and radar stations, powerful radio engineering facilities, industrial technological equipment, high-voltage power lines of industrial frequency, thermal shops, plasma, laser and X-ray installations, nuclear and nuclear reactors and so on. It should be noted that there are man-made sources of electromagnetic and other physical fields for special purposes, used in electronic countermeasures and placed on stationary and mobile objects on land, water, under water, and in the air.
Any technical device that uses or produces electrical energy is a source of EMFs emitted into external space. A peculiarity of exposure in urban conditions is the impact on the population of both the total electromagnetic background (integral parameter) and strong EMF from individual sources (differential parameter).
The main sources of electromagnetic fields (EMF) of radio frequencies are radio engineering facilities (RTO), television and radar stations (RLS), thermal shops and areas in areas adjacent to enterprises. Exposure to industrial frequency EMF is associated with high-voltage power lines (OHLs), sources of constant magnetic fields used in industrial enterprises. Zones with increased levels of EMF, the sources of which can be RTO and radar, have dimensions of up to 100...150 m. Moreover, inside buildings located in these zones, the energy flux density, as a rule, exceeds valid values.
Spectrum of electromagnetic radiation from the technosphere
An electromagnetic field is a special form of matter through which interaction between electrically charged particles occurs. An electromagnetic field in a vacuum is characterized by the vectors of electric field strength E and magnetic field induction B, which determine the forces acting on stationary and moving charges. In the SI system of units, the dimension of electric field strength [E] = V/m - volt per meter and the dimension of magnetic field induction [V] = T - tesla. The sources of electromagnetic fields are charges and currents, i.e. moving charges. The SI unit of charge is called the coulomb (C), and the unit of current is the ampere (A).
The forces of interaction of the electric field with charges and currents are determined by the following formulas:
F e = qE; F m = , (5.9)
where F e is the force acting on the charge from the electric field, N; q is the amount of charge, C; F M - force acting on the current from the magnetic field, N; j is the current density vector, indicating the direction of the current and equal in absolute value to A/m 2 .
The straight brackets in the second formula (5.9) denote the vector product of vectors j and B and form a new vector, the modulus of which is equal to the product of the moduli of vectors j and B multiplied by the sine of the angle between them, and the direction is determined by the right “gimlet” rule, i.e. . when rotating vector j to vector B along the shortest distance, vector . (5.10)
The first term corresponds to the force exerted by an electric field of intensity E, and the second to the magnetic force in a field with induction B.
The electric force acts in the direction of the electric field strength, and the magnetic force is perpendicular to both the speed of the charge and the magnetic field induction vector, and its direction is determined by the right-hand screw rule.
EMFs from individual sources can be classified according to several criteria, the most common of which is frequency. Non-ionizing electromagnetic radiation occupies a fairly wide frequency range from the ultra-low frequency (ULF) range of 0...30 Hz to the ultraviolet (UV) region, i.e. up to frequencies 3 1015 Hz.
The spectrum of man-made electromagnetic radiation extends from ultra-long waves (several thousand meters or more) to short-wave γ-radiation (with a wavelength of less than 10-12 cm).
It is known that radio waves, light, infrared and ultraviolet radiation, x-rays and γ-radiation are all waves of the same electromagnetic nature, differing in wavelength (Table 5.4).
Subbands 1...4 refer to industrial frequencies, subbands 5...11 - to radio waves. The microwave range includes waves with frequencies of 3...30 GHz. However, historically, the microwave range is understood as wave oscillations with a length of 1 m to 1 mm.
Table 5.4. Scale electromagnetic waves
|
Wavelength λ |
Wave subbands |
Oscillation frequency v |
Range |
|
No. 1...4. Ultra long waves |
|||
|
No. 5. Kilometer waves (LF - low frequencies) |
|||
|
No. 6. Hectometric waves (MF - middle frequencies) |
|||
|
Radio waves |
|||
|
No. 8. Meter waves (VHF - very high frequencies) |
|||
|
No. 9. Decimeter waves (UHF - ultra high frequencies) |
|||
|
No. 10. Centimeter waves (microwave - ultra high frequencies) |
|||
|
No. 11. Millimeter waves (millimeter wave) |
|||
|
0.1 mm (100 µm) |
Submillimeter waves |
||
|
Infrared radiation (IR range) |
4.3 10 14 Hz |
Optic range |
|
|
Visible range |
7.5 10 14 Hz |
||
|
Ultraviolet radiation(UV range) |
|||
|
X-ray range |
|||
|
γ-Radiation |
|||
|
Cosmic rays |
The optical range in radiophysics, optics, and quantum electronics refers to the range of wavelengths from approximately submillimeter to far ultraviolet radiation. The visible range includes vibrations of waves with lengths from 0.76 to 0.38 microns.
The visible range is a small part optical range. The boundaries of the transitions of UV radiation, X-ray, and γ-radiation are not exactly fixed, but approximately correspond to those indicated in the table. 5.4 values of λ and v. Gamma radiation, which has significant penetrating power, transforms into radiation of very high energies, called cosmic rays.
In table Table 5.5 shows some man-made sources of EMF operating in various ranges of the electromagnetic spectrum.
Table 5.5. Technogenic sources of EMF
|
Name |
Frequency range (wavelengths) |
|
Radio engineering objects |
30 kHz...30 MHz |
|
Radio transmitting stations |
30 kHz...300 MHz |
|
Radar and radio navigation stations |
Microwave range (300 MHz - 300 GHz) |
|
TV stations |
30 MHz...3 GHz |
|
Plasma installations |
Visible, IR, UV ranges |
|
Thermal installations |
Visible, IR range |
|
High voltage power lines |
Industrial frequencies, static electricity |
|
X-ray installations |
Hard UV, X-ray, visible light |
|
Optical range |
|
|
Microwave range |
|
|
Process installations |
HF, microwave, IR, UV, visible, X-ray ranges |
|
Nuclear reactors |
X-ray and γ-radiation, IR, visible, etc. |
|
Special-purpose EMF sources (ground, water, underwater, air) used in electronic countermeasures |
Radio waves, optical range, acoustic waves (combination of action) |
What is EMF, its types and classification
In practice, when characterizing the electromagnetic environment, the terms “electric field”, “magnetic field”, “electromagnetic field” are used. Let us briefly explain what this means and what connection exists between them.
An electric field is created by charges. For example, in all the well-known school experiments on the electrification of ebonite, an electric field is present.
A magnetic field is created when electric charges move through a conductor.
To characterize the magnitude of the electric field, the concept of electric field strength is used, symbol E, unit of measurement V/m (Volts-per-meter). The magnitude of the magnetic field is characterized by the magnetic field strength H, unit A/m (Ampere-per-meter). When measuring ultra-low and extremely low frequencies, the concept of magnetic induction B is also often used, the unit T (Tesla), one millionth of a T corresponds to 1.25 A/m.
By definition, an electromagnetic field is a special form of matter through which interaction occurs between electrically charged particles. Physical reasons The existence of an electromagnetic field is associated with the fact that a time-varying electric field E generates a magnetic field H, and a changing H generates a vortex electric field: both components E and H, continuously changing, excite each other. The EMF of stationary or uniformly moving charged particles is inextricably linked with these particles. With the accelerated movement of charged particles, the EMF “breaks away” from them and exists independently in the form of electromagnetic waves, without disappearing when the source is removed (for example, radio waves do not disappear even in the absence of current in the antenna that emitted them). 
Electromagnetic waves are characterized by wavelength, symbol - l (lambda). A source that generates radiation, and essentially creates electromagnetic oscillations, is characterized by frequency, designated f.
An important feature of EMF is its division into the so-called “near” and “far” zones. In the "near" zone, or induction zone, at a distance from the source r< l ЭМП можно считать квазистатическим.
Здесь оно быстро убывает с расстоянием,
обратно пропорционально квадрату r -2
или кубу r -3 расстояния. В "ближней"
зоне излучения электромагнитная волне
еще не сформирована. Для характеристики
ЭМП измерения переменного электрического
поля Е и переменного магнитного поля Н
производятся раздельно. Поле в зоне
индукции служит для формирования бегущих
составляющей полей (электромагнитной
волны), ответственных за излучение.
"Дальняя" зона - это зона
сформировавшейся электромагнитной
волны, начинается с расстояния r >3l. In the “far” zone, the field intensity decreases in inverse proportion to the distance to the source r -1. 
In the “far” zone of radiation there is a connection between E and H: E = 377H, where 377 is the wave impedance of the vacuum, Ohm. Therefore, as a rule, only E is measured. In Russia, at frequencies above 300 MHz, the electromagnetic energy flux density (PEF), or the Poynting vector, is usually measured. Denoted as S, the unit of measurement is W/m2. PES characterizes the amount of energy transferred by an electromagnetic wave per unit time through a unit surface perpendicular to the direction of propagation of the wave.
International classification of electromagnetic waves by frequency
|
Frequency range name |
Range limits |
Name of wave range |
Range limits |
|
Extreme low, ELF |
Decamegameter | ||
|
Ultra-low, SLF |
30 – 300 Hz |
Megameter | |
|
Infra-low, INF |
Hectokilometer |
1000 - 100 km |
|
|
Very low, VLF |
Myriameter | ||
|
Low frequencies, LF |
30 - 300 kHz |
Kilometer | |
|
Mids, mids |
Hectometric | ||
|
Treble, HF |
Decameter | ||
|
Very high, VHF |
30 - 300 MHz |
Meter | |
|
Ultra high, UHF |
decimeter | ||
|
Ultra high, microwave |
Centimeter | ||
|
Extremely high, EHF |
30 - 300 GHz |
Millimeter | |
|
Hyperhigh, HHF |
300 – 3000 GHz |
decimmillimeter |
2. Main sources of emp
Among the main sources of EMR are:
Personal computers
Electric transport (trams, trolleybuses, trains,...)
Power lines (city lighting, high voltage,...)
Electrical wiring (inside buildings, telecommunications,…)
Household electrical appliances
TV and radio stations (broadcasting antennas)
Satellite and cellular communications (broadcast antennas)
2.1 Electric transport
Electric vehicles - electric trains (including subway trains), trolleybuses, trams, etc. - are a relatively powerful source of magnetic field in the frequency range from 0 to 1000 Hz. According to (Stenzel et al., 1996), the maximum values of the magnetic induction flux density B in commuter trains reach 75 μT with an average value of 20 μT. The average value of V for vehicles with a DC electric drive was recorded at 29 µT. A typical result of long-term measurements of the levels of the magnetic field generated by railway transport at a distance of 12 m from the track is shown in the figure.
2.2 Power lines
The wires of a working power line create electric and magnetic fields of industrial frequency in the adjacent space. The distance over which these fields extend from the line wires reaches tens of meters. The range of propagation of the electric field depends on the voltage class of the power line (the number indicating the voltage class is in the name of the power line - for example, a 220 kV power line), the higher the voltage, the larger zone higher level electric field, while the dimensions of the zone do not change during the operation of the power line.
The range of propagation of the magnetic field depends on the magnitude of the current flowing or on the line load. Since the load on power lines can change repeatedly both during the day and with changing seasons, the size of the zone of increased magnetic field level also changes.
Biological action
Electric and magnetic fields are very strong factors influencing the state of all biological objects falling within the zone of their influence. For example, in the area of influence of the electric field of power lines, insects exhibit changes in behavior: for example, bees show increased aggressiveness, anxiety, decreased performance and productivity, and a tendency to lose queens; Beetles, mosquitoes, butterflies and other flying insects exhibit changes in behavioral responses, including a change in the direction of movement towards a lower field level.
Developmental anomalies are common in plants - the shapes and sizes of flowers, leaves, stems often change, and extra petals appear. Healthy man suffers from a relatively long stay in the field of power lines. Short-term exposure (minutes) can lead to a negative reaction only in hypersensitive people or in patients with certain types of allergies. For example, the work of English scientists in the early 90s is well known, showing that a number of allergy sufferers, when exposed to the power line field, develop an epileptic-type reaction. With prolonged stay (months - years) of people in the electromagnetic field of power lines, diseases can develop, mainly of the cardiovascular and nervous systems of the human body. In recent years, cancer has often been cited as a long-term consequence.
Sanitary standards
Studies of the biological effect of EMF IF, carried out in the USSR in the 60-70s, were focused mainly on the effect of the electrical component, since no significant biological effect of the magnetic component was experimentally discovered at typical levels. In the 70s, strict standards were introduced for the population according to EP, which are still among the most stringent in the world. They are set out in the Sanitary Norms and Rules “Protection of the population from the effects of the electric field created by overhead power lines of alternating current of industrial frequency” No. 2971-84. In accordance with these standards, all power supply facilities are designed and built.
Despite the fact that the magnetic field throughout the world is now considered the most dangerous to health, the maximum permissible magnetic field value for the population in Russia is not standardized. The reason is there is no money for research and development of standards. Most power lines were built without taking this danger into account.
Based on mass epidemiological surveys of the population living in conditions of irradiation by magnetic fields of power lines, a magnetic induction flux density of 0.2 - 0.3 µT.
Principles for ensuring public safety
The basic principle of protecting public health from the electromagnetic field of power lines is to establish sanitary protection zones for power lines and reduce the electric field strength in residential buildings and in places where people can stay for a long time by using protective screens.
The boundaries of sanitary protection zones for power transmission lines on existing lines are determined by the criterion of electric field strength - 1 kV/m.
Boundaries of sanitary protection zones for power lines according to SN No. 2971-84
|
Power line voltage | ||||
|
Size of sanitary protection (security) zone |
Boundaries of sanitary protection zones for power lines in Moscow
|
Power line voltage | |||||||
|
Size of sanitary protection zone |
The placement of ultra-high voltage overhead lines (750 and 1150 kV) is subject to additional requirements regarding the conditions of exposure to the electric field on the population. Thus, the closest distance from the axis of the designed 750 and 1150 kV overhead lines to the borders settlements should, as a rule, be at least 250 and 300 m, respectively.
How to determine the voltage class of power lines? It is best to contact your local energy company, but you can try visually, although this is difficult for a non-specialist:
330 kV - 2 wires, 500 kV - 3 wires, 750 kV - 4 wires. Below 330 kV, one wire per phase, can only be determined approximately by the number of insulators in the garland: 220 kV 10 -15 pcs., 110 kV 6-8 pcs., 35 kV 3-5 pcs., 10 kV and below - 1 pc. .
Permissible levels of exposure to the electric field of power lines
|
MPL, kV/m |
Irradiation conditions |
|
inside residential buildings |
|
|
on the territory of a residential development zone |
|
|
in populated areas outside of residential areas; (land of cities within the city limits within the boundaries of their long-term development for 10 years, suburban and green areas, resorts, lands of urban-type settlements within the village limits and rural settlements within the boundaries of these points) as well as in the territory of vegetable gardens and orchards; |
|
|
at the intersections of overhead power lines with highways of categories 1–IV; |
|
|
in uninhabited areas (undeveloped areas, even if frequently visited by people, accessible to transport, and agricultural land); |
|
|
in hard-to-reach areas (inaccessible to transport and agricultural vehicles) and in areas specially fenced off to exclude public access. |
Within the sanitary protection zone of overhead lines it is prohibited:
place residential and public buildings and structures;
arrange parking areas for all types of transport;
locate automobile servicing enterprises and oil and petroleum products warehouses;
carry out operations with fuel, repair machines and mechanisms.
The territories of sanitary protection zones are allowed to be used as agricultural land, but it is recommended to grow crops on them that do not require manual labor.
If in some areas the electric field strength outside the sanitary protection zone is higher than the maximum permissible 0.5 kV/m inside the building and higher than 1 kV/m in the residential area (in places where people may be present), they must measures should be taken to reduce tensions. To do this, on the roof of a building with a non-metal roof, almost any metal mesh is placed, grounded in at least two points. In buildings with a metal roof, it is enough to ground the roof in at least two points. In personal plots or other places where people are located, the power frequency field strength can be reduced by installing protective screens, for example, reinforced concrete, metal fences, cable screens, trees or shrubs at least 2 m high.
St. Petersburg State Polytechnic University
Department of Management in Socio-Economic Systems
Course work
Sources and characteristics of electromagnetic fields. Their effect on the human body. Standardization of electromagnetic fields.
Saint Petersburg
Introduction 3
General characteristics of the electromagnetic field 3
Characteristics of electromagnetic fields 3
Sources of electromagnetic fields 4
Impact of electromagnetic fields on the human body 5
Standardization of electromagnetic fields 5
Standardization of EMF for the population 10
Exposure control 14
Methods and means of protection against EM radiation 14
Shielding 14
Shielding of high-frequency thermal installations 14
Working element-inductor 15
Microwave protection 16
Radiation protection when setting up and testing microwave installations 17
Methods of protection against leakage through holes 18
Protection of the workplace and premises 18
Impact of laser radiation on humans 19
Standardization of laser radiation 19
Laser radiation measurement 20
Calculation of energy illumination in the workplace 20
Laser protection measures 21
First aid 22
List of sources 23
Introduction
In modern conditions of scientific and technological progress, as a result of the development of various types of energy and industry, electromagnetic radiation occupies one of the leading places in terms of its environmental and industrial significance among other environmental factors.
general characteristics electromagnetic field
An electromagnetic field is a special form of matter through which interaction between charged particles occurs. It represents the interconnected variables electric field and magnetic field. The mutual relationship between the electric and magnetic fields lies in the fact that any change in one of them leads to the appearance of the other: an alternating electric field generated by accelerated moving charges (source) excites an alternating magnetic field in adjacent regions of space, which, in turn, excites in adjacent regions of space have an alternating electric field, etc. Thus, the electromagnetic field propagates from point to point in space in the form of electromagnetic waves traveling from the source. Due to the finite speed of propagation, the electromagnetic field can exist autonomously from the source that generated it and does not disappear when the source is removed (for example, radio waves do not disappear when the current in the antenna that emitted them stops).
Characteristics of electromagnetic fields
It is known that near a conductor through which current flows, electric and magnetic fields arise simultaneously. If the current does not change over time, these fields are independent of each other. With alternating current, the magnetic and electric fields are interconnected, representing a single electromagnetic field.
The main characteristics of electromagnetic radiation are considered to be frequency, wavelength and polarization.
The frequency of an electromagnetic field is the number of times the field oscillates per second. The unit of measurement for frequency is the hertz (Hz), the frequency at which one oscillation occurs per second.
Wavelength is the distance between two points closest to each other that oscillate in the same phases.
Polarization is the phenomenon of directional oscillation of the vectors of electric field strength or magnetic field strength.
The electromagnetic field has a certain energy and is characterized by electrical and magnetic intensity, which must be taken into account when assessing working conditions.
Sources of electromagnetic fields
In general, the general electromagnetic background consists of sources of natural (electric and magnetic fields of the Earth, radio emission from the Sun and galaxies) and artificial (anthropogenic) origin (television and radio stations, power lines, household appliances). Sources of electromagnetic radiation also include radio engineering and electronic devices, inductors, thermal capacitors, transformers, antennas, flange connections of waveguide paths, microwave generators, etc.
Modern geodetic, astronomical, gravimetric, aerial photography, marine geodetic, engineering geodetic, geophysical work is carried out using instruments operating in the range of electromagnetic waves, ultra-high and ultra-high frequencies, exposing workers to danger with radiation intensity of up to 10 μW/cm 2.
Impact of electromagnetic fields on the human body
People do not see or feel electromagnetic fields, and that is why they do not always warn against the dangerous effects of these fields. Electromagnetic radiation has harmful effects on the human body. In the blood, which is an electrolyte, under the influence of electromagnetic radiation, ionic currents arise, causing tissue heating. At a certain radiation intensity, called the thermal threshold, the body may not be able to cope with the heat generated.
Heating is especially dangerous for organs with an underdeveloped vascular system with low blood circulation (eyes, brain, stomach, etc.). If your eyes are exposed to radiation for several days, the lens may become cloudy, which can cause cataracts.
In addition to thermal effects, electromagnetic radiation has an adverse effect on the nervous system and causes dysfunction of cardio-vascular system, metabolism.
Prolonged exposure to an electromagnetic field on a person causes increased fatigue, leads to a decrease in the quality of work operations, severe pain in the heart area, changes in blood pressure and pulse.
The risk of exposure to an electromagnetic field on a person is assessed based on the amount of electromagnetic energy absorbed by the human body.
Standardization of electromagnetic fields
EMF of any frequency has 3 conventional zones depending on the distance X to the source:
Induction zone (space with radius X 2);
Intermediate zone (diffraction zone);
Wave zone, Х2
Workplaces near sources of RF fields fall into the induction zone. For such sources, irradiation levels are normalized by the strength of the electric E(Vm) and magnetic H(A/m) fields.
GOST 12.1.006-84 installed remote control panels at the workplace throughout the working day:
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E |
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.,V/mThose working with a microwave generator fall into the wave zone. In these cases, the energy load on the human body is normalized W (μW*h/sq.m.) W = 200 μW*h/sq.m. – for all cases of irradiation, excluding irradiation from rotating and scanning antennas – for them W = 2000 µW*h/cm2. The maximum permissible energy flux density (MPD) σ additional (μW/cm2) is calculated using the formula σ additional = W / T, where T is the operating time in hours during the working day. In all cases, σ add ≤ 1000 μW/cm2.
National systems standards are the basis for the implementation of electromagnetic safety principles. As a rule, systems of standards include standards limiting the levels of electric fields (EF), magnetic fields (MF) and electromagnetic fields (EMF) of various frequency ranges by introducing maximum permissible exposure levels (MALs) for various exposure conditions and various populations.
In Russia, the system of electromagnetic safety standards consists of State Standards (GOST) and Sanitary Rules and Norms (SanPiN). These are interrelated documents that are binding throughout Russia.
State standards on standardization of permissible levels of exposure to electromagnetic fields are included in the group of the Occupational Safety Standards System - a set of standards containing requirements, norms and rules aimed at ensuring safety, maintaining human health and performance during the work process. They are the most common documents and contain:
requirements for the types of relevant hazardous and harmful factors;
maximum permissible values of parameters and characteristics;
general approaches to methods of monitoring standardized parameters and methods of protecting workers.
Russian state standards in the field of electromagnetic safety are given in Table 1.
Table 1.
State standards of the Russian Federation in the field of electromagnetic safety
|
Designation |
Name |
|
GOST 12.1.002-84 |
System of occupational safety standards. Electric fields of industrial frequency. Permissible voltage levels and control requirements |
|
GOST 12.1.006-84 |
System of occupational safety standards. Electromagnetic fields of radio frequencies. Permissible levels at workplaces and control requirements |
|
GOST 12.1.045-84 |
System of occupational safety standards. Electrostatic fields. Permissible levels at workplaces and control requirements |
Sanitary rules and regulations regulate hygienic requirements in more detail and in more specific exposure situations, as well as for individual types of products. Their structure includes the same main points as the State Standards, but sets them out in more detail. Usually, sanitary standards accompanied by Guidelines for monitoring the electromagnetic environment and carrying out protective measures.
Depending on the relationship of a person exposed to EMF to the radiation source in production conditions, Russian standards distinguish between two types of exposure: professional and non-professional. Occupational exposure conditions are characterized by a variety of generation modes and exposure options. In particular, near-field exposure usually involves a combination of general and local exposure. For non-occupational exposure, general exposure is typical. MRLs for professional and non-professional exposure are different. exposure on organism person. Knowledge of nature impact electromagnetic waves on organism person, ... through physical characteristics fields radiation in...
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Abstract >> Ecology... impact on our body. Ionizing radiation consists of particles (charged and uncharged) and quanta electromagnetic ... impact ionizing radiation based on knowledge of the properties of each type of radiation, characteristics their ... influence on organism person ...
Action on organism person electric current and first aid for victims of it
Laboratory work >>... impact on organism person ... their ... on open areas. Lowest illumination on semi ... sources; - determine the effectiveness of sound absorption and sound insulation means; - study characteristics ... electromagnetic arising during work electromagnetic ...
Impact toxic substances on organism person
Abstract >> Life safety... on health of offspring. Section I: CLASSIFICATION OF HARMFUL SUBSTANCES AND ROUTES THEIR INCOME IN ORGANISM PERSON... degrees impact on organism harmful substances are divided on four... characteristics environment. A consequence of the action of harmful substances on organism ...
Main sources of electromagnetic field
Among the main sources of EMF are:
Electric transport (trams, trolleybuses, trains, ...);
Power lines (city lighting, high-voltage, ...);
Electrical wiring (inside buildings, telecommunications, ...);
Household electrical appliances;
TV and radio stations (broadcasting antennas);
Satellite and cellular communications (broadcasting antennas);
Personal computers.
Electric transport. Electric transport – electric trains, trolleybuses, trams, etc. – is a relatively powerful source of magnetic field in the frequency range 0 ÷ 1000 Hz. Maximum values magnetic flux density IN in commuter trains they reach 75 µT with an average value of 20 µT. Average value IN in transport with a direct current electric drive it was recorded at 29 µT.
Power lines(Power lines). The wires of a working power line create electric and magnetic fields of industrial frequency in the adjacent space. The distance over which these fields extend from the line wires reaches tens of meters. The range of propagation of the electric field depends on the voltage class of the power line (the number indicating the voltage class is in the name of the power line - for example, a 220 kV power line), the higher the voltage, the larger the zone of increased electric field level, while the size of the zone does not change during the operation of the power line. The range of propagation of the magnetic field depends on the magnitude of the current flowing or on the line load. Since the load on power lines can change repeatedly both during the day and with changing seasons, the size of the zone of increased magnetic field level also changes.
Biological action. Electric and magnetic fields are very strong factors influencing the state of all biological objects falling within the zone of their influence. For example, in the area of influence of the electric field of power lines, insects exhibit changes in behavior: for example, bees show increased aggressiveness, anxiety, decreased performance and productivity, and a tendency to lose queens; Beetles, mosquitoes, butterflies and other flying insects exhibit changes in behavioral responses, including a change in the direction of movement towards a lower field level. Developmental anomalies are common in plants - the shapes and sizes of flowers, leaves, stems change, and extra petals appear. A healthy person suffers from a relatively long stay in the field of power lines. Short-term exposure (minutes) can lead to negative reaction only in hypersensitive people or in patients with certain types of allergies.
In recent years, cancer has often been cited as a long-term consequence.
Sanitary standards, despite the fact that the magnetic field throughout the world is now considered the most dangerous to health, the maximum permissible value of the magnetic field for the population is not standardized. Most of The power line was built without taking this danger into account. Based on mass epidemiological surveys of the population living in conditions of exposure to magnetic fields of power lines, as a safe or “normal” level for conditions of prolonged exposure, which does not lead to oncological diseases, independently of each other, Swedish and American experts recommended a magnetic flux density of 0.2 ÷ 0.3 µT. The basic principle of protecting public health from the electromagnetic field of power lines is to establish sanitary protection zones for power lines and reduce the electric field strength in residential buildings and in places where people may stay for a long time by using protective screens, the boundaries of sanitary protection zones for power lines on existing lines are determined by the criterion of electric field strength – 1 kV/m (tables 1.2 ÷ 1.4).
Table 1.2. Boundaries of sanitary protection zones for power lines
Table 1.4. Maximum permissible levels of exposure to the electric field of power lines
Continuation of Table 1.4
The placement of high-voltage lines (OHL) of ultra-high voltages (750 and 1150 kV) is subject to additional requirements regarding the conditions of exposure to the electric field on the population. Thus, the closest distance from the axis of the designed 750 and 1150 kV overhead lines to the boundaries of populated areas should, as a rule, be at least 250 and 300 m, respectively. How to determine the voltage class of power lines? It is best to contact your local power company, but you can try visually, although it is difficult for a non-specialist: 330 kV - two wires, 500 kV - three wires, 750 kV - four wires; below 330 kV - one wire per phase, can only be determined approximately by the number of insulators in the garland: 220 kV - 10 ÷ 15 pcs., 110 kV - 6 ÷ 8 pcs., 35 kV - 3 ÷ 5 pcs., 10 kV and below – 1 pc.
Maximum permissible levels (MAL). Within the sanitary protection zone of overhead lines it is prohibited:
Place residential and public buildings and structures;
Arrange parking areas for all types of transport;
Place automobile servicing enterprises and oil and petroleum products warehouses;
Perform operations with fuel, repair machines and mechanisms.
The territories of sanitary protection zones are allowed to be used as agricultural land, but it is recommended to grow crops on them that do not require manual labor. If in some areas the electric field strength outside the sanitary protection zone is higher than the maximum permissible 0.5 kV/m inside the building and higher than 1 kV/m in the residential area (in places where people may be present), they must measures should be taken to reduce tensions. To do this, almost any metal mesh, grounded at at least two points, is placed on the roof of a building with a non-metal roof. In buildings with a metal roof, it is sufficient to ground the roof at at least two points. On personal plots or other places where people are located, the power frequency field strength can be reduced by installing protective screens, for example, reinforced concrete, metal fences, cable screens, trees or shrubs at least two meters high.
Wiring. The greatest contribution to the electromagnetic environment of residential premises in the industrial frequency range of 50 Hz comes from the electrical equipment of the building, namely the cable lines supplying electricity to all apartments and other consumers of the building’s life support system, as well as distribution boards and transformers. In rooms adjacent to these sources, the level of the industrial frequency magnetic field, caused by the flowing electric current, is usually increased. The level of the electric field at industrial frequency is not high and does not exceed the maximum permissible limit for the population of 500 V/m.
Currently, many experts consider the maximum permissible value of magnetic induction to be 0.2 ÷ 0.3 µT. It is believed that the development of diseases - primarily leukemia - is very likely with prolonged exposure of a person to fields of higher levels (several hours a day, especially at night, for a period of more than a year).
The main protective measure is precautionary:
It is necessary to avoid prolonged stay (regularly for several hours a day) in places with high levels of industrial frequency magnetic fields;
The bed for night rest should be kept as far as possible from radiation sources; the distance to distribution cabinets and power cables should be 2.5 ÷ 3 meters;
If there are any unknown cables, distribution cabinets, transformer substations in or adjacent to the room, removal should be as much as possible; optimally, measure the EMF level before living in such a room;
If you need to install electrically heated floors, choose systems with reduced level magnetic field.
Household electrical appliances. All household appliances operating using electric current, are sources of EMF. The most powerful are microwave ovens, convection ovens, refrigerators with a “no frost” system, kitchen hoods, electric stoves, and televisions. The actual EMF generated, depending on the specific model and mode of operation, can vary greatly among equipment of the same type. The magnetic field values are closely related to the power of the device - the higher it is, the higher the magnetic field during its operation. The values of the electric field of industrial frequency of almost all electrical household appliances do not exceed several tens of V/m at a distance of 0.5 m, which is significantly less than the maximum limit of 500 V/m. (table 1.5 ÷ 1.6).
When staying in an apartment household appliances be guided by the following principles: place household electrical appliances as far as possible from rest areas, do not place household electrical appliances nearby and do not stack them on top of each other.
A microwave oven (or microwave oven) uses EMF, also called microwave radiation or microwave radiation, to heat food. The operating frequency of microwave radiation of microwave ovens is 2.45 GHz. It is this radiation that many people fear. However, modern microwave ovens are equipped with fairly advanced protection that prevents EMFs from escaping beyond the working volume. However, one cannot say that the field does not penetrate outside at all. microwave oven.
Table 1.5. Power frequency magnetic field levels of household electrical appliances at a distance of 0.3 m
For various reasons, part of the EMF intended for cooking the product penetrates outside, especially intensely, as a rule, in the area of the lower right corner of the door. To ensure safety when using ovens at home, there are sanitary standards that limit the maximum leakage of microwave radiation from a microwave oven. They are called “Maximum permissible levels of energy flux density created by microwave ovens” and have the designation SN No. 2666-83. According to these sanitary standards, the EMF energy flux density should not exceed 10 μW/cm 2 at a distance of 50 cm from any point of the furnace body when heating one liter of water. In practice, almost all new modern microwave ovens meet this requirement with a large margin. However, when purchasing a new stove, you need to make sure that the certificate of conformity states that your stove meets the requirements of these sanitary standards. It must be remembered that over time the degree of protection may decrease, mainly due to the appearance of microcracks in the door seal. This can happen either due to dirt or mechanical damage. Therefore, the door and its seal require careful handling and careful maintenance.
The guaranteed durability of protection against EMF leaks during normal operation is several years.
After five to six years of operation, it is advisable to check the quality of protection by inviting a specialist from a specially accredited laboratory for EMF monitoring. In addition to microwave radiation, the operation of a microwave oven is accompanied by an intense magnetic field created by an industrial frequency current of 50 Hz flowing in the oven's power supply system. At the same time, a microwave oven is one of the most powerful sources of a magnetic field in an apartment.
Table 1.6. Maximum permissible EMF levels for consumer products that are sources of EMF
| Source | Range | Remote control value | Measurement conditions |
| Induction furnaces | 20 ÷ 22 kHz | 500 V/m 4 A/m | Distance 0.3 m from the body |
| Microwave ovens | 2.45 GHz | 10 μW/cm 2 | Distance 0.50 ± 0.05 m from any point, with a load of 1 liter of water |
| PC video display terminal | 5 Hz ÷ 2 kHz | E Remote control = 25 V/m IN MPL = 250 nT | Distance 0.5 m around the PC monitor |
| 2 ÷ 400 kHz | E MPL = 2.5 V/mV MPL = 25 nT | ||
| surface electrostatic potential | V= 500 V | Distance 0.1 m from PC monitor screen | |
| Other products | 50 Hz | E= 500 V/m | Distance 0.5 m from the product body |
| 0.3 ÷ 300 kHz | E= 25 V/m | ||
| 0.3 ÷ 3 MHz | E= 15 V/m | ||
| 3 ÷ 30 MHz | E= 10 V/m | ||
| 30 ÷ 300 MHz | E= 3 V/m | ||
| 0.3 ÷ 30 GHz | PES = 10 μW/cm 2 |
TV and radio stations. Transmitting radio centers (RTC) are located in specially designated areas and can occupy quite a large areas(up to 1000 ha). In their structure, they include one or more technical buildings where radio transmitters and antenna fields are located, on which up to several dozen antenna-feeder systems (AFS) are located. The AFS includes an antenna used to measure radio waves and a feed line that supplies high-frequency energy generated by the transmitter to it. The zone of possible adverse effects of EMFs created by the PRC can be divided into two parts. The first part of the zone is the PRC territory itself, where all the services that ensure the operation of radio transmitters and AFS are located. This territory is guarded and only persons professionally associated with the maintenance of transmitters, switches and AFS are allowed into it. The second part of the zone is the territories adjacent to the PRC, access to which is not limited and where various residential buildings can be located, in this case there is a threat of exposure to the population located in this part of the zone. The location of the PRC can be different, for example, in Moscow and the Moscow region it is typically located in close proximity or among residential buildings. High levels of EMF are observed in areas, and often outside the location of transmitting radio centers of low, medium and high frequencies (PRC LF, MF and HF). A detailed analysis of the electromagnetic situation in the territories of the PRC indicates its extreme complexity associated with the individual nature of the intensity and distribution of EMF for each radio center. Due to this special studies This kind of work is carried out for each individual PRC. Widespread sources of EMF in populated areas are currently radio engineering transmitting centers (RTTCs), emitting ultrashort VHF and UHF waves into the environment.
A comparative analysis of sanitary protection zones (SPZ) and restricted development zones in the coverage area of such facilities showed that the highest levels of exposure to people and the environment are observed in the area where the “old-built” RTPC is located with an antenna support height of no more than 180 m. The largest contribution to the total The intensity of the impact is contributed by the “corner” three- and six-story VHF FM broadcasting antennas.
DV radio stations(frequencies 30 ÷ 300 kHz). In this range, the wavelengths are relatively long (for example, 2000 m for a frequency of 150 kHz). At a distance of one wavelength (or less) from the antenna the field can be quite large, for example, at a distance of 30 m from the antenna of a 500 kW transmitter operating at a frequency of 145 kHz, the electric field can be higher than 630 V/m, and the magnetic field higher 1.2 A/m.
CB radio stations(frequencies 300 kHz ÷ 3 MHz). Data for radio stations of this type say that the electric field strength at a distance of 200 m can reach 10 V/m, at a distance of 100 m - 25 V/m, at a distance of 30 m - 275 V/m (data are given for a 50 kW transmitter) .
HF radio stations(frequencies 3 ÷ 30 MHz). HF radio transmitters usually have lower power. However, they are more often located in cities; they can even be placed on the roofs of residential buildings at a height of 10 ÷ 100 m. A 100 kW transmitter at a distance of 100 m can create an electric field strength of 44 V/m and a magnetic field of 0.12 F/m.
TV transmitters are usually located in cities. Transmitting antennas are usually located at altitudes above 110 m. From the point of view of assessing the impact on health, field levels at distances from several tens of meters to several kilometers are of interest. Typical electric field strengths can reach 15 V/m at a distance of 1 km from a 1 MW transmitter. The problem of assessing the EMF level of television transmitters is relevant due to the sharp increase in the number of television channels and transmitting stations.
The main principle of ensuring safety is compliance with the maximum permissible levels of electromagnetic fields established by Sanitary Standards and Rules. Each radio transmitting facility has a Sanitary Passport, which defines the boundaries of the sanitary protection zone. Only with this document do the territorial bodies of the State Sanitary and Epidemiological Supervision permit the operation of radio transmitting facilities. They periodically monitor the electromagnetic environment to ensure it complies with the established remote controls.
Satellite connection. Satellite communication systems consist of a transceiver station on Earth and a satellite in orbit. The antenna pattern of satellite communication stations has a clearly defined narrowly directed main beam - the main lobe. The energy flux density (EFD) in the main lobe of the radiation pattern can reach several hundred W/m 2 near the antenna, also creating significant field levels at a large distance.
For example, a station with a power of 225 kW, operating at a frequency of 2.38 GHz, creates a PES equal to 2.8 W/m 2 at a distance of 100 km. However, energy dissipation from the main beam is very small and occurs most in the area where the antenna is located.
Cellular. Cellular radiotelephony is one of the most rapidly developing telecommunication systems today. The main elements of a cellular communication system are base stations (BS) and mobile radiotelephones (MRT). Base stations maintain radio communication with mobile radiotelephones, as a result of which BS and MRI are sources of electromagnetic radiation in the UHF range. Important feature cellular radio communication system is a very efficient use of the radio frequency spectrum allocated for the operation of the system (repeated use of the same frequencies, use various methods access), which makes it possible to provide telephone communications to a significant number of subscribers. The system uses the principle of dividing a certain territory into zones, or “cells,” with a radius of usually 0.5 ÷ 10 km. Base stations (BS) maintain communication with mobile radiotelephones located in their coverage area and operate in signal reception and transmission mode. Depending on the standard (Table 17), BS emit electromagnetic energy in the frequency range 463 ÷ 1880 MHz. BS antennas are installed at a height of 15 ÷ 100 m from the ground surface on existing buildings (public, office, industrial and residential buildings, chimneys of industrial enterprises, etc.) or on specially constructed masts. Among the BS antennas installed in one place, there are both transmitting (or transceiver) and receiving antennas, which are not sources of EMF. Based on the technological requirements for building a cellular communication system, the antenna radiation pattern in the vertical plane is designed in such a way that the main radiation energy (more than 90%) is concentrated in a rather narrow “beam”. It is always directed away from the structures on which the BS antennas are located, and above adjacent buildings, which is a necessary condition for the normal functioning of the system.
BS are a type of transmitting radio engineering objects, the radiation power of which (load) is not constant 24 hours a day. The load is determined by the presence of cell phone owners in the service area of a particular base station and their desire to use the phone for a conversation, which, in turn, fundamentally depends on the time of day, location of the BS, day of the week, etc. At night, the load of the BS is almost zero , i.e. the stations are mostly silent.
Table 1.7. Brief specifications cellular radio system standards
| Standard name | BS operating frequency range, MHz | MRI operating frequency range, MHz | Maximum radiated power of the BS, W | Maximum radiated power |
| MRI Cell radius NMT-450. Analog | 463 ÷ 467.5 | 453 ÷ 457.5 | 1 W; 1 ÷ 40 m | |
| AMPS. Analog | 869 ÷ 894 | 824 ÷ 849 | 0.6 W; 2 ÷ 20 km | |
| D-AMPS (IS-136). Digital | 869 ÷ 894 | 824 ÷ 849 | 0.2 W; 0.5 ÷ 20 km | |
| CDMA. Digital | 869 ÷ 894 | 824 ÷ 849 | 0.6 W; 2 ÷ 40 km | |
| GSM-900. Digital | 925 ÷ 965 | 890 ÷ 915 | 0.25 W; 0.5 ÷ 35 km | |
| GSM-1800 (DCS). Digital | 1805 ÷ 1880 | 1710 ÷ 1785 | 0.125 W; 0.5 ÷ 35 km |
Mobile radiotelephone(MRI) is a small-sized transceiver. Depending on the phone standard, transmission is carried out in the frequency range 453 ÷ 1785 MHz. The MRI radiation power is a variable quantity that largely depends on the state of the communication channel “mobile radiotelephone – base station”, i.e. The higher the BS signal level at the receiving site, the lower the MRI radiation power. The maximum power is in the range of 0.125 ÷ 1 W, but in real life it usually does not exceed 0.05 ÷ 0.2 W. The question of the impact of MRI radiation on the user’s body still remains open. Numerous studies conducted by scientists different countries on biological objects (including volunteers), led to ambiguous, sometimes contradictory, results. The fact remains undeniable that the human body “responds” to the presence of cell phone radiation.
When working mobile phone electromagnetic radiation is perceived not only by the base station receiver, but also by the user’s body, and, first of all, by his head. What happens in the human body, and how dangerous is this effect to health? There is still no clear answer to this question. However, an experiment by scientists showed that the human brain not only senses cell phone radiation, but also distinguishes between cellular communication standards.
Radar stations They are usually equipped with mirror-type antennas and have a narrowly directed radiation pattern in the form of a beam directed along the optical axis. Radar systems operate at frequencies from 500 MHz to 15 GHz, but individual systems can operate at frequencies up to 100 GHz. The EM signal they create is fundamentally different from radiation from other sources. This is due to the fact that periodic movement of the antenna in space leads to spatial intermittency of irradiation. Temporary intermittency of irradiation is due to the cyclical operation of the radar on radiation. The operating time in various operating modes of radio equipment can range from several hours to a day. Thus, for meteorological radars with a time intermittency of 30 minutes - radiation, 30 minutes - pause, the total operating time does not exceed 12 hours, while airport radar stations in most cases operate around the clock. The width of the radiation pattern in the horizontal plane is usually several degrees, and the duration of irradiation over the viewing period is tens of milliseconds. Metrological radars can create at a distance of 1 km PES ~ 100 W/m 2 for each irradiation cycle. Airport radar stations create PES ~ 0.5 W/m 2 at a distance of 60 m. Marine radar equipment is installed on all ships; it usually has a transmitter power an order of magnitude lower than that of airfield radars, so in normal mode scanning PES created at a distance several meters, does not exceed 10 W/m2. An increase in the power of radars for various purposes and the use of highly directional all-round antennas leads to a significant increase in the intensity of EMR in the microwave range and creates large areas on the ground with high density flow of energy. Most unfavourable conditions- in residential areas of cities within which airports are located.
Personal computers. The main source of adverse effects on the health of a computer user is the means of visual display of information on a cathode ray tube. The main factors of its adverse effects are listed below.
Ergonomic parameters of the monitor screen:
Reduced image contrast in conditions of intense external illumination;
Specular glare from the front surface of monitor screens;
There is flickering of the image on the monitor screen.
Emissive characteristics of the monitor:
Electromagnetic field of the monitor in the frequency range 20 Hz ÷ 1000 MHz;
Static electric charge on the monitor screen;
Ultraviolet radiation in the range of 200 ÷ 400 nm;
Infrared radiation in the range of 1,050 nm ÷ 1 mm;
X-ray radiation> 1.2 keV.
Computer as a source of alternating electromagnetic field. The main components of a personal computer (PC) are: the system unit (processor) and various input/output devices: keyboard, disk drives, printer, scanner, etc. Each personal computer includes a means of visually displaying information, called differently - a monitor, a display. As a rule, it is based on a device based on a cathode ray tube. PCs are often equipped with surge protectors (for example, “Pilot” type), uninterruptible power supplies and other auxiliary electrical equipment. All these elements during PC operation form a complex electromagnetic environment at the user’s workplace.
Table 1.8. Frequency range of PC elements
The electromagnetic field created by a personal computer has a complex spectral composition in the frequency range 0 ÷ 1000 MHz (Table 1.9). An electromagnetic field has an electric ( E) and magnetic ( N) components, and their relationship is quite complex, so the assessment E And N produced separately.
Table 1.9. Maximum EMF values recorded at the workplace
In terms of electromagnetic fields, the MPR II standard corresponds to the Russian sanitary standards SanPiN 2.2.2.542-96. “Hygienic requirements for video display terminals, personal computers and work organization.”
Means of protecting users from EMF. The main types of protective equipment offered are protective filters for monitor screens. They are used to limit the user's exposure to harmful factors from the monitor screen.
