Department of BJD
Test
discipline: Life safety
on the topic: Ionizing radiation
Perm, 2004
Introduction
Ionizing radiation is radiation whose interaction with the environment leads to the formation of electrical charges of different signs.
Ionizing radiation is the radiation that radioactive substances possess.
Under the influence of ionizing radiation, a person develops radiation sickness.
The main goal of radiation safety is to protect the health of the population, including personnel, from the harmful effects of ionizing radiation by observing the basic principles and standards of radiation safety without unjustified restrictions on useful activities when using radiation in various fields of economy, science and medicine.
Radiation safety standards (NRB-2000) are used to ensure human safety under conditions of exposure to ionizing radiation of artificial or natural origin.
Main characteristics of ionizing radiation
Ionizing radiation is radiation whose interaction with the environment leads to the formation of electrical charges of different signs. Sources of these radiations are widely used in technology, chemistry, medicine, agriculture and other fields, for example, when measuring soil density, detecting leaks in gas pipelines, measuring the thickness of sheets, pipes and rods, antistatic treatment of fabrics, polymerization of plastics, radiation therapy of malignant tumors, etc. However, it should be remembered that sources of ionizing radiation pose a significant threat to the health and life of the people who use them.
There are 2 types of ionizing radiation:
corpuscular, consisting of particles with a rest mass different from zero (alpha and beta radiation and neutron radiation);
electromagnetic (gamma radiation and x-rays) with a very short wavelength.
Alpha radiation is a stream of helium nuclei with high speed. These nuclei have a mass of 4 and a charge of +2. They are formed during radioactive decay of nuclei or during nuclear reactions. Currently, more than 120 artificial and natural alpha radioactive nuclei are known, which, emitting an alpha particle, lose 2 protons and 2 neurons.
The energy of alpha particles does not exceed several MeV (mega-electron volts). The emitted alpha particles move almost in a straight line at a speed of approximately 20,000 km/s.
The path length of a particle in air or other media is usually defined as the greatest distance from a radiation source at which the particle can still be detected before it is absorbed by the substance. The path length of a particle depends on the charge, mass, initial energy and the environment in which the movement occurs. With an increase in the initial energy of the particle and a decrease in the density of the medium, the path length increases. If the initial energy of the emitted particles is the same, then heavy particles have lower velocities than light ones. If the particles move slowly, then their interaction with the atoms of the medium is more effective and the particles quickly waste their available energy reserve.
The path length of alpha particles in air is usually less than 10 cm. Due to their large mass, when interacting with matter, alpha particles quickly lose their energy. This explains their low penetrating ability and high specific ionization: when moving in the air, an alpha particle forms several tens of thousands of pairs of charged particles – ions per 1 cm of its path.
Beta radiation is a flow of electrons or positrons produced during radioactive decay. Currently, about 900 beta radioactive isotopes are known.
The mass of beta particles is several tens of thousands of times less than the mass of alpha particles. Depending on the nature of the source of beta radiation, the speed of these particles can range from 0.3 to 0.99 times the speed of light. The energy of beta particles does not exceed several MeV, the path length in air is approximately 1800 cm, and in the soft tissues of the human body ~ 2.5 cm. The penetrating ability of beta particles is higher than that of alpha particles (due to their lower mass and charge).
Neutron radiation is a stream of nuclear particles that have no electrical charge. The mass of a neutron is approximately 4 times less than the mass of alpha particles. Depending on the energy, there are slow neutrons (with energy less than 1 KeV (kilo-electron-Volt) = 10 3 eV), neutrons of intermediate energies (from 1 to 500 KeV) and fast neutrons (from 500 KeV to 20 MeV). During the inelastic interaction of neutrons with the nuclei of atoms in the medium, secondary radiation appears, consisting of charged particles and gamma quanta (gamma radiation). During elastic interactions of neutrons with nuclei, ordinary ionization of matter can be observed. The penetrating ability of neutrons depends on their energy, but it is significantly higher than that of alpha or beta particles. Neutron radiation has a high penetrating ability and poses the greatest danger to humans of all types of corpuscular radiation. Neutron flux power is measured by the neutron flux density.
Gamma radiation is electromagnetic radiation with high energy and short wavelength. It is emitted during nuclear transformations or particle interactions. High energy (0.01 - 3 MeV) and short wavelength determine the greater penetrating power of gamma radiation. Gamma rays are not deflected by electric and magnetic fields. This radiation has less ionizing power than alpha and beta radiation.
X-ray radiation can be obtained in special X-ray tubes, in electron accelerators, in the environment surrounding a source of beta radiation, etc. X-ray radiation is one of the types of electromagnetic radiation. Its energy usually does not exceed 1 MeV. X-ray radiation, like gamma radiation, has a low ionizing ability and a large penetration depth.
To characterize the effect of ionizing radiation on a substance, the concept of radiation dose was introduced. Radiation dose is the portion of energy transferred by radiation to a substance and absorbed by it. A quantitative characteristic of the interaction of ionizing radiation and matter is absorbed dose of radiation(D), equal to the ratio of the average energy dE transferred by ionizing radiation to a substance in an elementary volume to the mass of the irradiated substance in this volume dm:
Until recently, the quantitative characteristics of only X-ray and gamma radiation, based on their ionizing effect, were taken exposure dose X is the ratio of the total electric charge dQ of ions of the same sign arising in a small volume of dry air to the air mass dm in this volume, i.e.
To assess the possible damage to health due to chronic exposure to ionizing radiation of arbitrary composition, the concept equivalent dose(N). This value is defined as the product of the absorbed dose D and the average radiation quality factor Q (dimensionless) at a given point in the tissue of the human body, i.e.:
There is another characteristic of ionizing radiation - dose rate X (absorbed, exposure or equivalent, respectively) representing the dose increment over a short period of time dx divided by this period dt. Thus, the exposure dose rate (x or w, C/kg s) will be:
X = W = dx / dt
The biological effect of the considered radiation on the human body is different.
Alpha particles, passing through matter and colliding with atoms, ionize (charge) them, knocking out electrons. In rare cases, these particles are absorbed by the nuclei of atoms, transforming them into a state of higher energy. This excess energy promotes the occurrence of various chemical reactions, which do not proceed or proceed very slowly without irradiation. Alpha radiation has a strong effect on the organic substances that make up the human body (fats, proteins and carbohydrates). On the mucous membranes, this radiation causes burns and other inflammatory processes.
Under the influence of beta radiation, radiolysis (decomposition) of water contained in biological tissues occurs with the formation of hydrogen, oxygen, hydrogen peroxide H 2 O 2, charged particles (ions) OH - and HO - 2. Water decomposition products have oxidizing properties and cause the destruction of many organic substances that make up the tissues of the human body.
The effect of gamma and X-ray radiation on biological tissues is mainly due to the free electrons generated. Neutrons, passing through a substance, produce the most powerful changes in it compared to other ionizing radiation.
Thus, the biological effect of ionizing radiation is reduced to a change in the structure or destruction of various organic substances (molecules) that make up the human body. This leads to disruption of the biochemical processes occurring in the cells, or even to their death, resulting in damage to the body as a whole.
There are external and internal irradiation of the body. External irradiation refers to the effect on the body of ionizing radiation from sources external to it. Internal irradiation is carried out by radioactive substances that enter the body through the respiratory organs, gastrointestinal tract or through the skin. Sources of external radiation - cosmic rays, natural radioactive sources found in the atmosphere, water, soil, food, etc., sources of alpha, beta, gamma, X-ray and neutron radiation used in technology and medicine, charged particle accelerators, nuclear reactors (including accidents at nuclear reactors) and a number of others.
Radioactive substances that cause internal irradiation of the body enter it when eating, smoking, or drinking contaminated water. The entry of radioactive substances into the human body through the skin occurs in rare cases (if the skin has damage or open wounds). Internal irradiation of the body lasts until the radioactive substance decays or is eliminated from the body as a result of physiological metabolic processes. Internal irradiation is dangerous because it causes long-term non-healing ulcers of various organs and malignant tumors.
When working with radioactive substances, operators' hands are exposed to significant radiation. Under the influence of ionizing radiation, chronic or acute (radiation burn) damage to the skin of the hands develops. Chronic damage is characterized by dry skin, cracking, ulceration and other symptoms. With acute damage to the hands, swelling, tissue necrosis, and ulcers occur, at the site of formation of which malignant tumors may develop.
Under the influence of ionizing radiation, a person develops radiation sickness. There are three degrees of it: first (mild), second and third (severe).
Symptoms of radiation sickness of the first degree are weakness, headaches, sleep and appetite disturbances, which intensify in the second stage of the disease, but they are additionally accompanied by disturbances in the activity of the cardiovascular system, metabolism and blood composition changes, and digestive organs become upset. At the third stage of the disease, hemorrhages, hair loss are observed, and the activity of the central nervous system and gonads is disrupted. People who have had radiation sickness have an increased likelihood of developing malignant tumors and diseases of the hematopoietic organs. Radiation sickness in its acute (severe) form develops as a result of irradiation of the body with large doses of ionizing radiation in a short period of time. The impact of small doses of radiation on the human body is dangerous, since this can lead to a violation of the hereditary information of the human body and mutations may occur.
A low level of development of a mild form of radiation sickness occurs at an equivalent radiation dose of approximately 1 Sv, a severe form of radiation sickness, in which half of all exposed persons die, occurs at an equivalent radiation dose of 4.5 Sv. A 100% fatal outcome from radiation sickness corresponds to an equivalent radiation dose of 5.5–7.0 Sv.
Currently, a number of chemical preparations (protectors) have been developed that significantly reduce the negative effect of ionizing radiation on the human body.
In Russia, the maximum permissible levels of ionizing radiation and the principles of radiation safety are regulated by the “Radiation Safety Standards” NRB-76, “Basic Sanitary Rules for Working with Radioactive Substances and Other Sources of Ionizing Radiation” OSP72-80. In accordance with these regulatory documents, exposure standards are established for the following three categories of persons:
For category A persons, the main dose limit is the individual equivalent dose of external and internal radiation per year (Sv/year), depending on the radiosensitivity of the organs (critical organs). This is the maximum permissible dose (MAD) - the highest value of the individual equivalent dose per year, which, with uniform exposure over 50 years, will not cause adverse changes in the health of personnel that can be detected by modern methods.
For category A personnel, the individual equivalent dose ( N, Sv), accumulated in the critical organ over time T(years) from the beginning of professional work, should not exceed the value determined by the formula:
N = traffic rules ∙ T. In addition, the dose accumulated by the age of 30 should not exceed 12 MDA.
For category B, a dose limit per year (PD, Sv/year) is established, which is understood as the highest average value of the individual equivalent dose per calendar year for a critical group of people, in which uniform exposure over 70 years cannot cause adverse changes in health, detected by modern methods. Table 1 shows the main dose limits of external and internal exposure depending on the radiosensitivity of organs.
Table 1 – Basic values of dose limits for external and internal exposure
Ionizing radiation causes a chain of reversible and irreversible changes in the body. The triggering mechanism for the effect is the processes of ionization and excitation of atoms and molecules in tissues. The dissociation of complex molecules as a result of the breaking of chemical bonds is a direct effect of radiation. A significant role in the formation of biological effects is played by radiation-chemical changes caused by the products of water radiolysis. Free radicals of hydrogen and hydroxyl groups, having high activity, enter into chemical reactions with molecules of protein, enzymes and other elements of biological tissue, which leads to disruption of biochemical processes in the body. As a result, metabolic processes are disrupted, tissue growth slows down and stops, and new chemical compounds appear that are not characteristic of the body. This leads to disruption of the activity of individual functions and systems of the body.
Chemical reactions induced by free radicals develop with great yield, involving hundreds and thousands of molecules not affected by radiation. This is the specificity of the action of ionizing radiation on biological objects. The effects develop over different periods of time: from a few seconds to many hours, days, years.
Ionizing radiation when exposed to the human body can cause two types of effects that are classified as diseases in clinical medicine: deterministic threshold effects (radiation sickness, radiation burn, radiation cataract, radiation infertility, abnormalities in fetal development, etc.) and stochastic (probabilistic) non-threshold effects (malignant tumors, leukemia, hereditary diseases).
Acute lesions develop with a single uniform gamma irradiation of the whole body and an absorbed dose above 0.5 Gy. At a dose of 0.25-0.5 Gy, temporary changes in the blood may be observed, which quickly return to normal. In the dose range of 0.5-1.5 Gy, a feeling of fatigue occurs, less than 10% of those exposed may experience vomiting and moderate changes in the blood. At a dose of 1.5-2.0 Gy, a mild form of acute radiation sickness is observed, which is manifested by prolonged lymphopenia, in 30-50% of cases - vomiting on the first day after irradiation. No deaths are recorded.
Moderate radiation sickness occurs at a dose of 2.5-4.0 Gy. Almost all irradiated people experience nausea and vomiting on the first day, the content of leukocytes in the blood sharply decreases, subcutaneous hemorrhages appear, in 20% of cases death is possible, death occurs 2-6 weeks after irradiation. At a dose of 4.0-6.0 Gy, a severe form of radiation sickness develops, leading in 50% of cases to death within the first month. At doses exceeding 6.0 Gy, an extremely severe form of radiation sickness develops, which in almost 100% of cases ends in death due to hemorrhage or infectious diseases. The data given refers to cases where there is no treatment. Currently, there are a number of anti-radiation agents that, with complex treatment, can eliminate death at doses of about 10 Gy.
Chronic radiation sickness can develop with continuous or repeated exposure to doses significantly lower than those that cause the acute form. The most characteristic signs of chronic radiation sickness are changes in the blood, a number of symptoms from the nervous system, local skin lesions, lesions of the lens, pneumosclerosis (with inhalation of plutonium-239), and a decrease in the body’s immunoreactivity.
The degree of exposure to radiation depends on whether the exposure is external (when a radioactive isotope enters the body) or internal. Internal exposure is possible through inhalation, ingestion of radioisotopes and their penetration into the body through the skin.
Some radioactive substances are absorbed and accumulated in specific organs, resulting in high local doses of radiation. Calcium, radium, strontium, etc. accumulate in bones, iodine isotopes cause damage to the thyroid gland, rare earth elements cause mainly liver tumors. Cesium and rubidium isotopes are evenly distributed, causing inhibition of hematopoiesis, atrophy of the testes, and soft tissue tumors. In internal irradiation, the most dangerous are the alpha-emitting isotopes of polonium and plutonium.
The ability to cause long-term consequences: leukemia, malignant neoplasms, early aging is one of the insidious properties of ionizing radiation.
Hygienic regulation of ionizing radiation carried out by Radiation Safety Standards NRB-99 (Sanitary Rules SP 2.6.1.758-99). Basic radiation dose limits and permissible levels are established for the following categories of exposed persons:
- - personnel - persons working with man-made sources (group A) or who, due to working conditions, are in the sphere of their influence (group B);
- - the entire population, including personnel, outside the scope and conditions of their production activities.
For categories of exposed persons, three classes of standards are established: main dose limits - PD (Table 3.13), permissible levels corresponding to the main dose limits, and control levels.
Table 3.13. Basic dose limits (extracted from NRB-99)
* For persons of group B, all dose limits should not exceed 0.25 dose limits of group A.
Dose equivalent to NT n - absorbed dose in an organ or tissue From n, multiplied by the appropriate weighting factor for a given radiation UY:
The unit of measurement for equivalent dose is J o kg-1, which has a special name - sievert (Sv).
The value of Nd for photons, electrons and muons of any energy is 1, for a-particles, fission fragments, heavy nuclei - 20.
Effective dose - a value used as a measure of the risk of long-term consequences of irradiation of the entire human body and its individual organs, taking into account their radiosensitivity. It is the sum of the products of the equivalent dose in the organ NxT by the corresponding weighting factor for a given organ or tissue ]¥t:
Where NxT- equivalent dose in tissue G during time t.
The unit of measurement for the effective dose, as well as the equivalent dose, is J o kg" (sievert).
V/y values for individual types of tissue and organs are given below.
Type of tissue, organ: ¥t
gonads........................................................ ...........................................0.2
Bone marrow................................................ ...............................0.12
liver, mammary gland, thyroid gland....................0.05
leather................................................. ...........................................0.01
Basic radiation dose limits do not include doses from natural and medical exposures, as well as doses resulting from radiation accidents. There are special restrictions on these types of exposure.
The effective dose for personnel should not exceed 1000 mSv over a working period (50 years), and 7 mSv for the population over a lifetime (70 years).
In table 3.14 shows the values of permissible radioactive contamination of working surfaces, leather, workwear, safety shoes, and personal protective equipment for personnel.
Table 3.14. Permissible levels of radioactive contamination of working surfaces, leather, workwear, safety shoes and personal protective equipment, part/(cm-1 - min) (extract from NRB-99)
|
Object of pollution |
a-active nuclides |
(i-active nuclides |
|
|
separate |
other |
||
|
Intact skin, towels, special underwear, the inner surface of the front parts of personal protective equipment |
|||
|
Basic workwear, the inner surface of additional personal protective equipment, the outer surface of safety shoes |
|||
|
The outer surface of additional personal protective equipment removed in sanitary locks |
|||
|
Surfaces of premises for periodic stay of personnel and equipment located in them |
|||
Ionizing radiation is a phenomenon associated with radioactivity.
Radioactivity is the spontaneous transformation of the nuclei of atoms of one element into another, accompanied by the emission of ionizing radiation.
The degree, depth and shape of radiation injuries that develop among biological objects when exposed to ionizing radiation primarily depend on the amount of absorbed radiation energy. To characterize this indicator, the concept of absorbed dose is used, i.e., radiation energy absorbed per unit mass of the irradiated substance.
Ionizing radiation is a unique environmental phenomenon, the consequences of which on the body, at first glance, are not at all equivalent to the amount of energy absorbed.
The most important biological reactions of the human body to the action of ionizing radiation are conventionally divided into two groups:
1) acute lesions;
2) long-term consequences, which in turn are divided into somatic and genetic effects.
At radiation doses of more than 100 rem, acute radiation sickness develops, the severity of which depends on the radiation dose.
Long-term somatic consequences include a variety of biological effects, the most significant of which are leukemia, malignant neoplasms, and reduced life expectancy.
Regulation of exposure and principles of radiation safety. Since January 1, 2000, exposure of people in the Russian Federation has been regulated by radiation safety standards (NRB-96), hygienic standards (GN) 2.6.1.054-96. Basic radiation dose limits and permissible levels are established for the following categories of exposed persons:
1) personnel - persons working with man-made sources (group A) or who are under working conditions in an area of influence (group B);
2) the population, including personnel, outside the scope and conditions of their production activities.
For these categories of irradiated people, three classes of standards are provided:
1) main dose limits (maximum permissible dose - for category A, dose limit - for category B);
2) acceptable levels;
3) control levels established by the administration of the institution in agreement with the State Sanitary and Epidemiological Supervision at a level below the permissible level.
Basic principles of ensuring radiation safety:
1) reducing the power of sources to minimum values;
2) reducing the time spent working with sources;
3) increasing the distance from sources to workers;
4) shielding of radiation sources with materials that absorb ionizing radiation.
-
Ionizing radiation And security radiation security. Ionizing radiation is a phenomenon associated with radioactivity. Radioactivity is the spontaneous transformation of the nuclei of atoms of one element into another... -
Ionizing radiation And security radiation security. Ionizing radiation -
Ionizing radiation And security radiation security. Ionizing radiation is a phenomenon associated with radioactivity. Radioactivity is spontaneous. -
Ionizing radiation And security radiation security. Ionizing radiation is a phenomenon associated with radioactivity. Radioactivity is spontaneous... more ». -
Norms radiation security. The human body is constantly exposed to cosmic rays and natural radioactive elements present in the air, soil, and in the tissues of the body itself.”
For ionizing radiation The traffic limit is 5 rem per year. -
In accordance with the above, the Russian Ministry of Health approved standards in 1999 radiation security(NRB-99)
Exposure dose - based on ionizing action radiation, this is a quantitative characteristic of the field ionizing radiation. -
Currently, radiation damage to people can be associated with violation of rules and regulations radiation security when working with sources ionizing radiation, during accidents at radiation hazardous facilities, during nuclear explosions, etc. -
5) multiple sources ionizing radiation both closed and open types
Legislation on nuclear and radiation security combines legal acts of varying legal force. -
security
Anti-radiation shelters are structures that protect people from ionizing radiation, contamination with radioactive substances, droplets of hazardous substances and... -
Just download the cheat sheets security vital activity - and no exam is scary for you!
level of noise, infrasound, ultrasound, vibration - increased or decreased barometric pressure - increased level ionizing radiation-increased...
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Sources of electromagnetic radiation
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 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 radiation are 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/cm2.
Biological effects of electromagnetic radiation
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 a harmful effect 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, causing dysfunction of the cardiovascular system and 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, 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.
3.2.1.2 Electric fields of industrial frequency currents
It has been established that electromagnetic fields of industrial frequency currents (characterized by an oscillation frequency from 3 to 300 Hz) also have a negative impact on the body of workers. The adverse effects of industrial frequency currents appear only at magnetic field strengths of the order of 160-200 A/m. Often the magnetic field strength does not exceed 20-25 A/m, so it is enough to assess the danger of exposure to an electromagnetic field based on the magnitude of the electric field strength.
To measure the strength of electric and magnetic fields, devices of the IEMP-2 type are used. Radiation flux density is measured by various types of radar testers and low-power thermistor meters, for example, “45-M”, “VIM”, etc.
Protection against electric fields
In accordance with the standard "GOST 12.1.002-84 SSBT. Electric fields of industrial frequency. Permissible voltage levels and requirements for monitoring at workplaces." norms for permissible levels of electric field strength depend on the time a person spends in the dangerous zone. The presence of personnel at the workplace for 8 hours is allowed at an electric field strength (E) not exceeding 5 kV/m. At electric field strength values of 5-20 kV/m, the time of permissible stay in the work area in hours is:
T=50/E-2. (3.1)
Work under conditions of irradiation with an electric field with a intensity of 20-25 kV/m should last no more than 10 minutes.
In a work area characterized by different electric field strengths, personnel stay is limited to the following time (in hours):
where and TE are, respectively, the actual and permissible time of stay of personnel (hours) in controlled areas with tensions E1, E2, ..., En.
The main types of collective protection against the influence of the electric field of industrial frequency currents are shielding devices. Shielding can be general or separate. With general shielding, the high-frequency installation is covered with a metal casing - a cap. The installation is controlled through windows in the walls of the casing. For safety reasons, the casing is in contact with the installation ground. The second type of general shielding is isolating the high-frequency installation into a separate room with remote control.
Structurally, shielding devices can be made in the form of canopies, canopies or partitions made of metal ropes, rods, meshes. Portable screens can be designed in the form of removable canopies, tents, shields, etc. Screens are made of sheet metal with a thickness of at least 0.5 mm.
Along with stationary and portable shielding devices, individual shielding kits are used. They are designed to protect against the effects of an electric field whose intensity does not exceed 60 kV/m. Individual shielding kits include: overalls, safety shoes, head protection, as well as hand and face protection. The components of the kits are equipped with contact terminals, the connection of which allows for a unified electrical network and high-quality grounding (usually through shoes).
The technical condition of shielding kits is periodically checked. The test results are recorded in a special journal.
Field topographic and geodetic work can be carried out near power lines. The electromagnetic fields of high- and ultra-high-voltage overhead power lines are characterized by magnetic and electric strengths of up to 25 A/m and 15 kV/m, respectively (sometimes at a height of 1.5-2.0 m from the ground). Therefore, in order to reduce the negative impact on health, when carrying out field work near power lines with voltages of 400 kV and above, it is necessary to either limit the time spent in the danger zone or use personal protective equipment.
3.2.1.3 Radio frequency electromagnetic fields
Sources of radio frequency electromagnetic fields
The sources of electromagnetic fields of radio frequencies are: radio broadcasting, television, radar, radio control, hardening and melting of metals, welding of non-metals, electrical prospecting in geology (radio wave transmission, induction methods, etc.), radio communications, etc.
Low frequency electromagnetic energy 1-12 kHz is widely used in industry for induction heating for the purpose of hardening, melting, and heating metal.
The energy of a pulsed electromagnetic field of low frequencies is used for stamping, pressing, for joining various materials, casting, etc.
When dielectric heating (drying wet materials, gluing wood, heating, heat setting, melting plastics) settings are used in the frequency range from 3 to 150 MHz.
Ultrahigh frequencies are used in radio communications, medicine, radio broadcasting, television, etc. Work with ultrahigh frequency sources is carried out in radar, radio navigation, radio astronomy, etc.
Biological effects of electromagnetic fields of radio frequencies
In terms of subjective sensations and objective reactions of the human body, there are no special differences observed when exposed to the entire range of HF, UHF and microwave radio waves, but the manifestations and unfavorable consequences of exposure to microwave electromagnetic waves are more typical.
The most characteristic effects of radio waves of all ranges are deviations from the normal state of the central nervous system and the human cardiovascular system. What is common in the nature of the biological action of electromagnetic fields of high intensity radio frequencies is the thermal effect, which is expressed in the heating of individual tissues or organs. The lens of the eye, gall bladder, bladder and some other organs are especially sensitive to the thermal effect.
Subjective sensations of exposed personnel include complaints of frequent headaches, drowsiness or insomnia, fatigue, lethargy, weakness, increased sweating, darkening of the eyes, absent-mindedness, dizziness, loss of memory, causeless feelings of anxiety, fear, etc.
To the listed adverse effects on humans, one should add the mutagenic effect, as well as temporary sterilization when irradiated with intensities above the thermal threshold.
To assess the potential adverse effects of electromagnetic waves of radio frequencies, acceptable energy characteristics of the electromagnetic field for different frequency ranges are adopted - electric and magnetic strength, energy flux density.
Protection from radio frequency electromagnetic fields
To ensure the safety of work with sources of electromagnetic waves, systematic monitoring of the actual values of standardized parameters is carried out at workplaces and in places where personnel may be located. If operating conditions do not meet the requirements of the standards, then the following protection methods are used:
1. Shielding the workplace or radiation source.
2. Increasing the distance from the workplace to the radiation source.
3. Rational placement of equipment in the work area.
4. Use of preventive protective equipment.
5. The use of special energy power absorbers to reduce radiation at the source.
6. Use of remote control and automatic control capabilities, etc.
Workplaces are usually located in an area of minimal electromagnetic field intensity. The final link in the chain of engineering protective equipment is personal protective equipment. As personal means of protecting the eyes from microwave radiation, special safety glasses are recommended, the glasses of which are coated with a thin layer of metal (gold, tin dioxide).
Protective clothing is made of metallized fabric and is used in the form of overalls, gowns, jackets with hoods, with safety glasses built into them. The use of special fabrics in protective clothing can reduce radiation exposure by 100-1000 times, that is, by 20-30 decibels (dB). Safety glasses reduce the radiation intensity by 20-25 dB.
In order to prevent occupational diseases, it is necessary to conduct preliminary and periodic medical examinations. Women during pregnancy and breastfeeding should be transferred to other jobs. Persons under 18 years of age are not allowed to work with radio frequency generators. Persons who have contact with sources of microwave and UHF radiation are provided with benefits (shortened working hours, additional leave).
Radiation called the ray-like spread of something from the center to the circumference.
There are different types of radiation that, unlike visible light and heat, are not perceived by our senses. Man lives in a world where there are no places where there is no radiation. It is believed that the ability of radioactive radiation to cause mutations was the main reason for the continuous evolution of biological species. According to biologists, since the beginning of life on Earth, about 1 billion species of living organisms have evolved. Currently, according to various estimates, there are from 2 to 15 million species of flora and fauna left. Without the effects of radiation, our planet probably would not have such a variety of life forms. The presence of background radiation is one of the mandatory conditions for life on Earth; radiation is as necessary for life as light and heat. With a slight increase in background radiation, metabolism in the human body improves somewhat; with a decrease in background radiation, the growth and development of living organisms slows down by 30 - 50%. With “zero” radiation, plant seeds stop growing and living organisms stop reproducing. Therefore, you should not succumb to radiophobia - fear of radiation, but you need to know what threat high levels of radiation pose, learn to avoid it, and, if necessary, survive in conditions of radiation danger. Natural radiation is a natural component of the human environment. Conventionally, radiation can be divided into ionizing and non-ionizing. Non-ionizing radiation is light, radio waves, radioactive heat from the Sun. This type of radiation does not cause damage to the human body, although it does have harmful effects at high intensity. Radiation is considered ionizing in the event that it is capable of breaking the chemical bonds of the molecules that make up living organisms. For simplicity, ionizing radiation is simply called radiation, and its quantitative characteristic is called dose. To record the indicators and characteristics of radioactive radiation, special devices are used - dosimeters And radiometers.
The normal radiation background is considered to be 10 - 16 µR/h.
Under the influence of natural background radiation, a person is exposed to external and internal radiation. Sources external irradiation - This is cosmic radiation and natural radioactive substances located on the surface and in the depths of the Earth, in the atmosphere, water, and plants. Cosmic radiation includes galactic And sunny radiation. The intensity of cosmic radiation depends on geomagnetic latitude (increases from the equator to northern latitudes) and altitude above sea level. Compared to the dose of cosmic radiation received by people near the equator, at the latitude of Moscow it increases 1.5 times, at an altitude of 2 km - by 3 times, at 4 km - by 6 times, in an airplane at an altitude of 12 km - by 150 times. The level of cosmic radiation increases significantly during solar flares.
The main amount of natural radioactive substances is contained in the rocks that make up the thickness of the earth's crust. They are distributed unevenly in the earth's crust, depending on the type of rock; Accordingly, the radiation dose for people living in different places will be different. There are 5 geographical areas on Earth where the natural background radiation is significantly increased. These places are located in Brazil, India, France, Egypt and the island of Nitz in the Pacific Ocean. Thus, on some beaches in the resort town of Guarapari (Brazil), the radiation level exceeds the norm by about 500 times. This is due to the fact that the city stands on sands rich in thorium.
Internal exposure 2/3 of human exposure from natural sources comes from the ingestion of radioactive substances into the body with food, drinking water, and inhaled air. Quite often, radionuclides enter the human body through so-called food or biological chains. For example, a radionuclide in the soil enters plants with water, the plants are eaten by a cow, and together with the milk or meat from this cow, the radioactive substance enters the human body.
The greatest contribution to natural internal human exposure comes from radioactive gas - radon. This gas is released everywhere from the earth's crust. With prolonged exposure to radon, a person can develop cancer. According to the UN Scientific Committee on the Effects of Atomic Radiation, almost 20% of all lung cancer cases can be caused by exposure to radon and its decay products. The concentration of radon indoors is 8 times higher than outdoors. Radon provides 44% of the total radiation dose in Russia.
Emergence of sources artificial radiation contributed to an increase in the radiation load on humans. People are periodically exposed to radiation from televisions, computers, medical X-ray machines, radioactive fallout from nuclear weapons testing, and as a result of the operation of nuclear power plants.
Essential source increasing background radiation on the planet - accidents at nuclear power plants. The reasons for such emergency situations are varied - from errors in the work of personnel and wear and tear of equipment to malicious intent. There is a high probability of terrorist attacks on nuclear power plants. In isolated cases, emergencies at nuclear power plants can develop into disasters causing enormous damage. In 2004, 4 accidents involving the release of radioactive substances were registered at enterprises of the Russian Federation (0 in 2005).
Currently, there are about 45 thousand nuclear warheads in the world. During nuclear explosions, radiation damage to people occurs due to penetrating radiation and radioactive contamination of the area (Fig. 3.7).
Fig.3.7.
Penetrating radiation - a stream of gamma rays and neutrons emitted from the nuclear explosion zone in all directions for several seconds.
Nuclear pollution - This is the result of a huge amount of radioactive substances falling out of the explosion cloud. Falling onto the earth's surface, they create a contaminated area called a radioactive trace.
Artificial and natural radioactive radiation are similar in nature and can have harmful effects on human health.
Action
ionizing radiation:
- the effect of radiation on the body is imperceptible to humans (people do not have sense organs that would perceive ionizing radiation);
- ionizing radiation can have a harmful effect on human health (the boundaries between the harm and benefit of radiation have not yet been established, therefore any ionizing radiation should be treated as dangerous);
- the individual characteristics of the human body appear only with small doses of radiation (the younger the person, the higher his sensitivity to radiation; starting from the age of 25, a person becomes most resistant to radiation);
- the greater the radiation dose received by a person, the higher the likelihood of developing radiation sickness;
- visible lesions of the skin, malaise characteristic of radiation sickness, do not appear immediately, but only some time later;
- the summation of doses occurs secretly (over time, radiation doses add up, which leads to radiation diseases).
As a result of exposure to radiation, the flow of biochemical processes and metabolism in the human body is disrupted. Depending on the absorbed dose and the individual characteristics of the organism, changes may be reversible or irreversible. With a small dose, the affected tissue restores its functional activity; a large dose with prolonged exposure can cause irreversible damage to individual organs or the entire body as a whole.
In the event of an emergency involving ionizing radiation, all measures must be taken to ensure that the dose received is as small as possible. There are three effective ways to protect against radiation: protection by time, protection by distance, protection by shielding and absorption (Fig. 3.8).
Rice. 3.8.
Time protection implies limiting the time spent in areas or objects affected by radioactive contamination (the shorter the period of time, the lower the radiation dose received).
Under protection by distance refers to the evacuation of people from places where high levels of radiation are observed or expected.
In conditions where evacuation is impossible, it is carried out protection by shielding and absorption. This method of protection uses shelters, shelters and personal protective equipment.
Notification of the population about radioactive contamination is organized by the emergency response authorities.
"Radiation Hazard"- a signal that is given when the beginning of radioactive contamination of a given populated area (region) is detected or when there is a threat of radioactive contamination within the next hour. It is communicated to the population via local radio and television networks, as well as sirens. After being notified of a radiation hazard, the public should immediately act in accordance with the recommendations received through the media.