A research project on the topic: “Electrical safety” was prepared by a 2nd year student of the “Electrostal College” group of the UG (Protected Soil Vegetable Grower) 17-01 Shaikin Ilya Olegovich.
The goal of the project is to convey to the audience comprehensive information on electrical safety issues and to warn students against injury associated with inappropriate behavior and operation of faulty electrical equipment.
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State budgetary professional educational institution of the Moscow region "Elektrostal College" Research project On the topic: Electrical safety. Prepared by: student of group OZ G 17-01 Shaikin Ilya Olegovich
Abstract The goal of the project is to convey to the audience comprehensive information on electrical safety issues and to warn people against inappropriate behavior and operation of faulty electrical equipment.
What is electrical safety? Electrical safety is a system of organizational measures and technical means that prevent harmful and dangerous effects on workers from electric current, electric arc, electromagnetic field and static electricity.
What are the dangers of electric current? Electric current has significant features that distinguish its danger from danger from other harmful and dangerous production factors (for example, emitting thermal, light energy, etc.).
The first feature of electric current is that it cannot be sensed remotely by a person due to the fact that a person does not have the appropriate sensory organs. Therefore, the body’s protective reaction manifests itself only after exposure to electric current.
The second feature of electric current is that, flowing through the human body, it exerts its effect not only at points of contact and on the path through the body, but also causes a reflex effect, disrupting the normal activity of individual organs and systems of the human body (nervous, cardiovascular , breathing, etc.).
The third feature is the danger of electrical injury without direct contact with live parts - when moving on the ground (floor) near a damaged electrical installation (in case of a ground fault), through an electric arc.
Classification of protective equipment. Electrical protective equipment includes: - electrical insulating rods of all types (operational, measuring, for grounding installation); - electrical insulating and electrical clamps; - voltage indicators of all types and voltage classes; - hand-held electrical insulating tool; - electrically insulating gloves, boots and galoshes, carpets and stands;
Electrically insulating ladders and stepladders; - fencing devices; - electrically insulating pads and caps; - individual voltage indicators; - portable groundings, including throw-on ones; - ladders and stepladders made of electrically insulating fiberglass.
Conclusion. There are many types of dangers when working with electrical devices and electrical installations, so all precautions must be taken, and since in the event of an accident the urgent arrival of doctors is unlikely, everyone working with electricity must be able to provide first aid.
Introduction. 2
Chapter 1. The effect of electric current on the human body. 3
Chapter 2. Factors influencing the outcome of a person’s electric shock8
Chapter 3. Conditions and causes of electric shock. 10
Chapter 4. Measures to protect against electric shock. 12
Chapter 5. Providing primary care in case of electric shock. 16
Conclusion. 19
List of used literature... 20
The electrical saturation of modern production creates electrical hazards, the source of which can be electrical networks, electrified equipment and tools, computer and organizational equipment that runs on electricity. This determines the relevance of the problem of electrical safety - the elimination of electrical injuries.
Electrical safety is a system of organizational and technical measures and means that ensure the protection of people from the harmful and dangerous effects of electric current, electric arc, electromagnetic field and static electricity.
Electrical injuries make up a small percentage compared to other types of industrial injuries, however, they rank among the first in terms of the number of injuries with severe and especially fatal outcomes. An analysis of work-related injuries in the meat industry shows that on average about 18% of all serious and fatal injuries occur as a result of electric shock. The largest number of electrical injuries (60-70%) occur while working on electrical installations with voltages up to 1000 V. This is explained by the widespread use of such installations and the relatively low level of training of the persons operating them. There are significantly fewer electrical installations over 1000 V in operation and they are serviced by specially trained personnel, which results in fewer electrical injuries.
Electric current, passing through the human body, has biological, electrolytic, thermal and mechanical effects.
Biological effect current manifests itself in irritation and excitation of tissues and organs. As a result, skeletal muscle spasms are observed, which can lead to respiratory arrest, avulsion fractures and dislocations of the limbs, and spasm of the vocal cords.
Electrolytic action current manifests itself in the electrolysis (decomposition) of liquids, including blood, and also significantly changes the functional state of cells.
Thermal effect Electric current leads to burns of the skin, as well as death of subcutaneous tissues, including charring.
Mechanical action current manifests itself in tissue separation and even separation of body parts.
There are two main types of damage to the body: electrical injuries and electrical shocks. Often both types of lesions accompany each other. However, they are different and should be considered separately.
Electrical injuries– these are clearly expressed local violations of the integrity of body tissues caused by exposure to electric current or electric arc. Usually these are superficial injuries, that is, damage to the skin and sometimes other soft tissues, as well as ligaments and bones.
The danger of electrical injuries and the difficulty of their treatment are determined by the nature and extent of tissue damage, as well as the body's response to this damage. Typically, injuries heal and the victim's ability to work is restored fully or partially. Sometimes (usually with severe burns) a person dies. In such cases, the direct cause of death is not the electric current, but local damage to the body caused by the current. Typical types of electrical injuries are electrical burns, electrical marks, skin metallization, electroophthalmia, and mechanical injuries.
Electrical burns- the most common electrical injuries. They make up 60-65%, and 1/3 of them are accompanied by other electrical injuries.
There are burns: current (contact) and arc.
Contact electrical burns, i.e. Tissue damage at the entry, exit points and along the path of electric current occurs as a result of human contact with a live part. These burns occur when operating electrical installations of relatively low voltage (no higher than 1-2 kV), and they are relatively mild.
An arc burn is caused by an electrical arc that creates a high temperature. Arc burns occur when working in electrical installations of various voltages and are often the result of accidental short circuits in installations from 1000 V to 10 kV or erroneous personnel operations. The defeat occurs from a change in the electric arc or clothing that catches fire from it.
There may also be combined injuries (contact electrical burn and thermal burn from an electric arc flame or flaming clothing, electrical burn in combination with various mechanical injuries, electrical burn simultaneously with thermal burn and mechanical injury).
Electrical signs are clearly defined spots of gray or pale yellow color on the surface of the skin of a person exposed to current. The signs are round or oval in shape with a depression in the center. They come in the form of scratches, small wounds or bruises, warts, hemorrhages in the skin and calluses. Sometimes their shape matches the shape of the live part that the victim touched, and also resembles the shape of wrinkles.
In most cases, electric signs are painless, and their treatment ends well: over time, the upper layer of skin and the affected area acquire their original color, elasticity and sensitivity. Signs occur in approximately 20% of victims of electric current.
Metallization of leather- penetration into its upper layers of metal particles melted under the action of an electric arc. This is possible in case of short circuits, disconnectors and circuit breakers tripping under load, etc.
The affected area has a rough surface, the color of which is determined by the color of the metal compounds that have gotten under the skin: green - in contact with copper, gray - with aluminum, blue-green - with brass, yellow-gray - with lead. Usually, over time, the diseased skin goes away and the affected area takes on a normal appearance. At the same time, all painful sensations associated with this injury disappear.
Metallization of the skin is observed in approximately every tenth of the victims. Moreover, in most cases, simultaneously with metallization, an electric arc burn occurs, which almost always causes more severe injuries.
Electroophthalmia– inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet rays, causing chemical changes in the body’s cells. Such irradiation is possible in the presence of an electric arc (for example, during a short circuit), which is a source of intense radiation not only of visible light, but also of ultraviolet and infrared rays. Electroophthalmia occurs relatively rarely (in 1-2% of victims), most often during electric welding work.
Mechanical damage are the result of sharp, involuntary convulsive muscle contractions under the influence of current passing through a person. As a result, ruptures of the skin, blood vessels and nerve tissue can occur, as well as joint dislocations and even bone fractures. These injuries are usually serious injuries that require long-term treatment. Fortunately, they occur rarely - in no more than 3% of victims of electric shock.
Electric shock- this is the excitation of living tissues by an electric current passing through the body, accompanied by involuntary convulsive muscle contractions. Depending on the outcome of the negative impact of current on the body, electric shocks can be divided into the following four degrees:
I - convulsive muscle contraction without loss of consciousness;
II - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;
III - loss of consciousness and disturbance of cardiac activity or breathing (or both);
IV - clinical death, that is, lack of breathing and blood circulation.
Clinical (or “imaginary”) death is a transition period from life to death, occurring from the moment of cessation of activity and the lungs. A person in a state of clinical death lacks all signs of life, he does not breathe, his heart does not work, painful stimuli do not cause any reactions, the pupils of the eyes are dilated and do not react to light. However, during this period, life in the body has not yet completely died out, because its tissues do not die immediately and the functions of various organs do not immediately fade away.
The first to die are the brain cells, which are very sensitive to oxygen starvation and whose activity is associated with consciousness and thinking. Therefore, the duration of clinical death is determined by the time from the moment of cessation of cardiac activity and breathing until the beginning of the death of cells in the cerebral cortex; in most cases it is 4-5 minutes, and if a healthy person dies from an accidental cause, for example, from electric current, it is 7-8 minutes.
Biological (or true) death is an irreversible phenomenon characterized by the cessation of biological processes in the cells and tissues of the body and the breakdown of protein structures; it occurs after a period of clinical death.
Causes of death from electric shock include cardiac arrest, respiratory failure, and electrical shock.
The cessation of cardiac activity is a consequence of the effect of current on the heart muscle. Such an effect can be direct, when the current flows directly in the heart area, and reflexive, that is, through the central nervous system, when the current path lies outside this area. In both cases, cardiac arrest may occur or fibrillation may occur, that is, chaotically fast and multi-temporal contractions of the fibers (fibrils) of the heart muscle, during which the heart stops working as a pump, as a result of which blood circulation in the body stops.
Cessation of breathing as the primary cause of death from electric current is caused by the direct or reflex effect of the current on the muscles of the chest involved in the breathing process. A person begins to experience difficulty breathing even at a current of 20-25 mA (50 Hz), which intensifies with increasing current. With prolonged exposure to current, asphyxia can occur - suffocation as a result of a lack of oxygen and excess carbon dioxide in the body.
Electric shock is a kind of severe neuro-reflex reaction of the body in response to strong irritation by electric current, accompanied by dangerous disorders of blood circulation, breathing, metabolism, etc. The state of shock lasts from several tens of minutes to a day. After this, either the death of the body may occur as a result of complete extinction of vital functions, or complete recovery as a result of timely active therapeutic intervention.
The severity of electric shock depends on a number of factors: the value of the current, the electrical resistance of the human body and the duration of the flow of current through it, the path of the current, the type and frequency of the current, the individual properties of the person and environmental conditions,
Current strength is the main factor determining one or another degree of damage to a person (path: arm-arm, arm-legs).
Fibrillation is the name given to chaotic and multi-temporal contractions of the heart muscle fibers, completely disrupting its functioning as a pump. (For women, the threshold current values are 1.5 times less than for men).
Direct current is approximately 4-5 times safer than 50 Hz alternating current. However, this is typical for relatively low voltages (up to 250-300 V). At higher voltages, the danger of DC current increases.
In the voltage range 400-600 V, the danger of direct current is almost equal to the danger of alternating current with a frequency of 50 Hz, and at a voltage of more than 600 V, direct current is more dangerous than alternating current.
Electrical resistance of the human body with dry, clean and intact skin at a voltage of 15-20 V, it ranges from 3000 to 100,000 Ohms, and sometimes more. When the top layer of skin is removed, the resistance decreases to 500-700 Ohms. When the skin is completely removed, the resistance of the internal tissues of the body is only 300-500 Ohms. For calculations, the resistance of the human body is assumed to be 1000 Ohms.
If there are various damages on the skin (scuffs, cuts, abrasions), its electrical resistance in these places sharply decreases.
The electrical resistance of the human body decreases with increasing current and the duration of its passage due to increased local heating of the skin, which leads to vasodilation, and, consequently, to an increased supply of blood to this area and an increase in sweat production.
With an increase in the voltage applied to the human body, the skin resistance decreases, and, consequently, the total resistance of the body, which approaches its lowest value of 300-500 Ohms. This is explained by the breakdown of the stratum corneum of the skin, an increase in the current passing through it, and other factors.
The resistance of the human body depends on the gender and age of people: in women this resistance is less than in men, in children it is less than in adults, in young people it is less than in the elderly. This is explained by the thickness and degree of coarsening of the top layer of skin. A short-term (several minutes) decrease in the resistance of the human body (20-50%) causes external, unexpectedly occurring physical stimuli: pain (blows, injections), light and sound.
Electrical resistance is also affected by the type of current and its frequency. At frequencies of 10-20 kHz, the upper layer of skin practically loses its resistance to electric current.
In addition, there are particularly vulnerable areas of the body to the effects of electric current. These are the so-called acupuncture zones (face area, palms, etc.) with an area of 2-3 mm 2. Their electrical resistance is always less than the electrical resistance of zones lying outside the acupuncture zones.
Duration of current flow through the human body greatly influences the outcome of the lesion due to the fact that over time the resistance of the human skin decreases, and heart damage becomes more likely.
Current path through the human body is also essential. The greatest danger arises when current directly passes through vital organs. Statistics show that the number of injuries with loss of consciousness when current passes along the “right arm-legs” path is 87%; along the “leg-leg” path - 15%, The most characteristic current circuits through a person: arm-legs, arm-arm, arm-torso (56.7, 12.2 and 9.8% of injuries, respectively). But the most dangerous are considered to be those current circuits in which both arms are involved - both legs, left arm-legs, arm-arm, head-legs.
Type and frequency of current also affect the degree of damage. The most dangerous is alternating current with a frequency from 20 to 1000 Hz. Alternating current is more dangerous than direct current, but this is typical only for voltages up to 250 -300 V; At higher voltages, direct current becomes more dangerous. As the frequency of alternating current passing through the human body increases, the impedance of the body decreases and the passing current increases. However, a decrease in resistance is possible only within frequencies from 0 to 50-60 Hz. A further increase in the frequency of the current is accompanied by a decrease in the danger of injury, which completely disappears at a frequency of 450-500 kHz. But these currents can cause burns both when an electric arc occurs and when they pass directly through the human body. The decrease in the danger of electric shock with increasing frequency is almost noticeable at a frequency of 1000-2000 Hz.
Individual properties of a person and the state of the environment also have a significant influence on the severity of the lesion.
A person may be injured by an electric shock or arc in the following cases:
· in case of single-phase (single) contact of a person isolated from the ground with non-insulated live parts of electrical installations that are energized;
· when a person simultaneously touches two non-insulated parts of electrical installations that are energized;
· when a person who is not isolated from the ground approaches a dangerous distance from live parts of electrical installations that are not protected by insulation;
· when a person not isolated from the ground touches non-current-carrying metal parts (casings) of electrical installations that are energized due to a short circuit on the casing;
· under the influence of atmospheric electricity during a lightning discharge;
· as a result of the action of an electric arc;
· when releasing another person under tension.
The following causes of electrical injuries can be identified:
Technical reasons– non-compliance of electrical installations, protective equipment and devices with safety requirements and conditions of use, associated with defects in design documentation, manufacturing, installation and repair; malfunctions of installations, protective equipment and devices that arise during operation.
Organizational and technical reasons- non-compliance with technical safety measures at the stage of operation (maintenance) of electrical installations; untimely replacement of faulty or outdated equipment and the use of installations that were not put into operation in the prescribed manner (including homemade ones).
Organizational reasons- failure to perform or incorrect implementation of organizational safety measures, inconsistency of the work performed with the task.
Organizational and social reasons :
· work overtime (including work to eliminate the consequences of accidents);
· inconsistency of work with specialty;
· violation of labor discipline;
· permission to work on electrical installations for persons under 18 years of age;
· attracting to work persons who have not been formalized by an order for employment in the organization;
· permission to work for persons with medical contraindications.
When considering the causes, it is necessary to take into account the so-called human factors. These include both psychophysiological and personal factors (a person’s lack of individual qualities necessary for this work, a violation of his psychological state, etc.), and socio-psychological factors (unsatisfactory psychological climate in the team, living conditions, etc.).
According to the requirements of regulatory documents, the safety of electrical installations is ensured by the following basic measures:
1) inaccessibility of live parts;
2) proper, and in some cases increased (double) insulation;
3) grounding or grounding of electrical equipment housings and electrical installation elements that may be energized;
4) reliable and fast automatic protective shutdown;
5) the use of reduced voltages (42 V and below) to power portable pantographs;
6) protective separation of circuits;
7) blocking, warning alarms, inscriptions and posters;
8) use of protective equipment and devices;
9) carrying out scheduled maintenance and preventive testing of electrical equipment, devices and networks in operation;
10) carrying out a number of organizational activities (special training, certification and re-certification of electrical personnel, briefings, etc.).
To ensure electrical safety at meat and dairy industry enterprises, the following technical methods and means of protection are used: protective grounding, grounding, the use of low voltages, control of winding insulation, personal protective equipment and safety devices, protective disconnecting devices.
Protective grounding- This is the intentional electrical connection to the ground or its equivalent of metallic non-current-carrying parts that may be energized. It protects against electric shock when touching metal casings of equipment, metal structures of electrical installations, which become energized due to failure of electrical insulation.
The essence of the protection is that during a short circuit, the current flows through both parallel branches and is distributed between them in inverse proportion to their resistances. Since the resistance of the man-to-ground circuit is many times greater than the resistance of the body-to-ground circuit, the strength of the current passing through the person is reduced.
Depending on the location of the grounding electrode relative to the equipment being grounded, remote and loop grounding devices are distinguished.
Remote grounding switches are located at a certain distance from the equipment, while the grounded housings of electrical installations are on the ground with zero potential, and a person touching the housing is under the full voltage of the grounding switch.
Loop grounding switches are placed along the contour around the equipment in close proximity, so the equipment is located in the current flow zone. In this case, when there is a short circuit to the housing, the ground potential on the territory of an electrical installation (for example, a substation) acquires values close to the potential of the ground electrode and grounded electrical equipment, and the touch voltage decreases.
Zeroing- this is an intentional electrical connection with a neutral protective conductor of metal non-current-carrying parts that may be energized. With such an electrical connection, if it is reliably made, any short circuit to the housing turns into a single-phase short circuit (i.e. a short circuit between the phases and the neutral wire). In this case, a current of such strength arises that the protection (fuse or circuit breaker) is activated and the damaged installation is automatically disconnected from the supply network.
Low voltage- voltage not exceeding 42 V, used to reduce the risk of electric shock. Low AC voltages are obtained using step-down transformers. It is used when working with portable power tools, when using portable lamps during installation, dismantling and repair of equipment, as well as in remote control circuits.
Isolation of the workplace– this is a set of measures to prevent the occurrence of a human-earth current circuit and increase the value of the transition resistance in this circuit. This protective measure is used in cases of increased risk of electric shock and usually in combination with an isolating transformer.
The following types of insulation are distinguished:
· working – electrical insulation of live parts of an electrical installation, ensuring its normal operation and protection from electric shock;
· additional – electrical insulation provided in addition to the working insulation to protect against electric shock in the event of damage to the working insulation;
· double – electrical insulation, consisting of working and additional insulation. Double insulation consists of one electrical receiver having two stages of insulation independent of one another (for example, covering electrical equipment with a layer of insulating material - paint, film, varnish, enamel, etc.). The use of double insulation is most rational when, in addition to the working electrical insulation of live parts, the body of the electrical receiver is made of insulating material (plastic, fiberglass).
Safety shutdown- this is a fast-acting protection that ensures automatic shutdown of an electrical installation when there is a danger of electric shock.
It should ensure automatic shutdown of electrical installations in the event of single-phase (single-pole) contact with parts energized that are not permissible for humans, and (or) when a leakage (short circuit) current exceeding specified values occurs in the electrical installation.
Protective shutdown is recommended as a primary or additional protective measure if safety cannot be ensured by grounding or grounding, or if grounding or grounding is difficult to implement or is not practical for economic reasons. Devices (devices) for protective shutdown with regard to reliability of operation must meet special technical requirements.
Personal protective equipment is divided into insulating, auxiliary and fencing.
Insulating protective equipment provides electrical isolation of a person from live parts and the ground. They are divided into basic (dielectric gloves, tools with insulated handles) and additional (dielectric galoshes, mats, stands)
Auxiliary items include goggles, gas masks, and masks designed to protect against light, thermal and mechanical influences.
Boundaries include portable shields, cages, insulating pads, portable grounds and posters. They are intended mainly for temporary fencing of live parts that may be touched by workers.
All personnel servicing electrical installations must be trained annually in techniques for releasing electric current, performing artificial respiration and external cardiac massage. Classes are conducted by competent medical personnel with practical training on simulators. The manager of the enterprise is responsible for organizing training.
If a person touches live parts that are energized with his hand, this causes an involuntary convulsive contraction of the muscles of the hand, after which he is no longer able to free himself from the live parts. Therefore, the first action of the person providing assistance is to immediately turn off the electrical installation that the victim is touching. Disabling is done using switches, knife switches, unscrewing plugs and other methods. If the victim is at a height, then when turning off the installation it is necessary to ensure that he does not fall.
If it is difficult to turn off the installation, then it is necessary to free the victim, using all means of protection, so as not to become energized yourself.
At voltages up to 1000 V, you can use a dry board or stick to free the victim from the wire that has fallen on him. You can also pull dry clothes, while avoiding touching metal parts and open areas of the victim’s body; You need to act with one hand, holding the other behind your back. It is safest for the person providing assistance to use dielectric gloves and rubber mats when freeing the victim. After releasing the victim from the electric current, it is necessary to assess the victim’s condition in order to provide appropriate first aid.
If the victim is conscious, breathing and pulse are stable, then it is necessary to lay him on a mat; unbutton clothes; create an influx of fresh air; create complete peace by observing your breathing and pulse. Under no circumstances should the victim be allowed to move, as the condition may worsen. Only a doctor can decide what to do next. If the victim breathes very rarely and convulsively, but his pulse is palpable, it is necessary to immediately begin artificial respiration.
If the victim has no consciousness, breathing, pulse, or dilated pupils, then we can assume that he is in a state of clinical death. In this case, it is necessary to urgently begin to revive the body using artificial respiration using the mouth-to-mouth method and external cardiac massage. If within just 5-6 minutes after the cessation of cardiac activity you do not begin to revive the victim’s body, then without air oxygen the brain cells die and death turns from clinical to biological; the process will become irreversible. Therefore, the five-minute time limit is the deciding factor for revival.
With the help of indirect cardiac massage in combination with artificial respiration, anyone can bring the victim back to life or time will be gained until the resuscitation team arrives.
The development of technology changes human working conditions, but does not make them safer; on the contrary, during the operation of new technology, previously unknown dangerous factors often appear.
Modern production is unthinkable without the widespread use of electric power. There is probably no professional activity where electric current is not used.
The negative consequences for human health that emerge during the operation of technological equipment have now made ensuring industrial safety one of the most pressing technical and socio-economic problems.
The most terrible consequence of electric shock is death. Fortunately, it happens quite rarely in this case.
To prevent electrical shock and ensure electrical safety in production, the following is used: insulation of wires and other components of electrical circuits, instruments and machines; protective grounding; zeroing, emergency power outage; personal protective equipment and some other measures.
Unfortunately, the widespread aging of production assets and deterioration of premises also negatively affects the quality of electrical wiring. Breakdowns in electrical wiring not only lead to electric shocks, but are also one of the main causes of fires.
1. Occupational safety. Industrial safety: textbook. allowance / L.L. Nikiforov, V.V. Persiyanov. – M.: MGUPB, 2006. – 257 p.
2. Labor protection in the meat and dairy industry / A.M. Medvedev, I.S. Antsypovich, Yu.N. Vinogradov. – M.: Agropromizdat, 1989. – 256 p.: ill. – (Textbooks and teaching aids for technical school students).
3. Labor protection in the energy sector. Ed. B.A. Knyazevsky. M., "Energoatomizdat", 1985.
4. Textbook manual for universities / V.E. Anofrikov, S.A. Bobok, M.N. Dudko, G.D. Elistratov/GUU. M., ZAO Finstatinform, 1999.
I Introduction. Electricity, a set of phenomena caused by the existence, movement and interaction of charged bodies or particles.
IIMain part. Electrical safety.
1. Medicine about electrical injuries.
2. Causes of electric shock
3. Electrical injuries and the state of half-rooms
4. Precautions when working with electrical appliances.
5. Measures to help in case of electric shock.
6. Legal liability when working with electric current.
7. “Life situations”
8. Danger of lightning.
9. Electric field and protection from it.
III Conclusion. Physics and ecology of everyday life.
I Introduction
ELECTRICITY(from the Greek elektron - amber), a set of phenomena in which the existence, movement and interaction (through an electromagnetic field) of charged particles is revealed. The study of electricity is one of the main branches of physics.
Electricity is often understood as electrical energy, for example, when talking about the use of electricity in the national economy; the meaning of the term “electricity” changed in the process of development of physics and technology.
ELECTRICITY, a set of phenomena caused by the existence, movement and interaction of charged bodies or carrier particles electric charges.
The interaction of stationary electric charges is carried out through an electrostatic field. Moving charges (electric current), along with the electric field, also excite a magnetic field, that is, they generate an electromagnetic field, through which electromagnetic interactions are carried out. Thus, electricity is inextricably linked with magnetism. Electromagnetic phenomena are described by classical electrodynamics, which is based on the equations Maxwell.
Origin of the terms "electricity" and "magnetism"
The simplest electrical and magnetic phenomena have been known since ancient times. Near the city of Magnesia in Asia Minor, amazing stones were found (based on their location they were called magnetic, or magnets), which attracted iron. In addition, the ancient Greeks discovered that a piece of amber (Greek elektron, electron) rubbed on wool could lift up small scraps of papyrus. The terms “magnetism”, “electricity” and their derivatives owe their origin to the words “magnet” and “electron”.
The classical theory of electricity covers a huge set of electromagnetic processes. Among the four types of interactions - electromagnetic, gravitational, strong (nuclear) and weak, existing in nature, electromagnetic interactions occupy first place in the breadth and variety of manifestations. In everyday life, with the exception of attraction to the Earth and tides in the ocean, a person encounters mainly only manifestations of electromagnetic forces. In particular, the elastic force of steam is of an electromagnetic nature. Therefore, the change from the “age of steam” to the “age of electricity” only meant a change from an era when they did not know how to control electromagnetic forces to an era when they learned to manage these forces at their own discretion.
It is difficult to even list all the manifestations of electrical (more precisely, electromagnetic) forces. They determine the stability of atoms, combine atoms into molecules, and determine the interaction between atoms and molecules, leading to the formation of condensed (liquid and solid) bodies. All types of elasticity and friction forces also have an electromagnetic nature.
The role of electrical forces in the nucleus of an atom is great. In a nuclear reactor and during the explosion of an atomic bomb, it is these forces that accelerate fragments of nuclei and lead to the release of enormous energy. Finally, interaction between bodies is carried out through electromagnetic waves - light, radio waves, thermal radiation, etc.
Main features of electromagnetic forces
Electromagnetic forces are not universal. They act only between electrically charged particles. Nevertheless, they determine the structure of matter and physical processes in a wide spatial range of scales - from 10-13 to 107 cm (at smaller distances, nuclear interactions become decisive, and at larger distances, gravitational forces must also be taken into account). The main reason is that matter is made up of electrically charged particles - negative - electrons and positive atomic nuclei. It is the existence of charges of two signs - positive and negative - that ensures the action of both attractive forces between unlike charges and repulsive forces between like charges, and these forces are very large compared to gravitational ones.
As the distance between charged particles increases, electromagnetic forces slowly (inversely proportional to the square of the distance) decrease, like gravitational forces. But charged particles form neutral systems - atoms and molecules, the forces of interaction between which manifest themselves only at very short distances. The complex nature of electromagnetic interactions is also significant: they depend not only on the distances between charged particles, but also on their speeds and even accelerations.
II Main partThe widespread practical use of electrical phenomena began only in the second half of the 19th century, after the creation of classical electrodynamics by J. C. Maxwell.
Invention of the radio and G. Marconi- one of the most important applications of the principles of the new theory. For the first time in human history, scientific research preceded technical applications. If the steam engine was built long before the creation of the theory of heat (thermodynamics), then it was possible to construct an electric motor or implement radio communication only after the discovery and study of the laws of electrodynamics.
The widespread use of electricity is due to the fact that electrical energy can be easily transmitted through wires over long distances and, most importantly, converted using relatively simple devices into other types of energy: mechanical, thermal, radiation energy, etc. The laws of electrodynamics underlie all electrical engineering and radio engineering, including television, video recording and almost all communications. The theory of electricity forms the foundation of such current areas of modern science as plasma physics and the problem of controlled thermonuclear reactions, laser optics, magnetohydrodynamics, astrophysics, the design of computers, particle accelerators, etc.
Countless practical applications of electromagnetic phenomena have transformed the lives of people around the globe. Humanity has created an “electrical environment” around itself - with a ubiquitous electric light bulb and a plug socket on almost every wall.
Medicine about electrical injuries
Children and adults often mishandle electrical appliances, putting their lives in danger. There are known cases of electrical injuries in our city, some of them with a tragic outcome. The danger of working with electrical appliances lies in the fact that current and voltage do not have external signs that would allow a person, using the senses (vision, hearing, smell), to detect the impending danger and take precautions. As you know, the human body is a conductor. If someone accidentally touches live parts of an electrical installation, exposed wires or live terminals, an electric current will flow through their body. As a result, a person may receive electrical injury. We all deal with electrical appliances all the time. To avoid electric shock, it is necessary to know the effects of current on the human body; factors on which the damaging effect of current depends; how to prevent electrical injuries and how to provide first aid in case of electric shock.
Electrical injuries - damage to organisms by electric current - occur in industry, agriculture, transport, and at home. They can also be caused by atmospheric electricity (lightning).
The severity of damage to the body depends on the strength of the current, voltage, duration of the current and its type (constant or alternating). It has been established that alternating current is the most dangerous. The danger increases with increasing voltage. The longer the exposure to current, the more severe the electrical injury.
Current causes various local and general disorders in the body. Local phenomena (at the point of contact) can vary from minor pain to severe burns with charring and burning of individual parts of the body. General phenomena are expressed in disruption of the central nervous system, respiratory and circulatory systems. With electrical injuries, there is fainting, loss of consciousness, speech disorders, convulsions, breathing problems (even stopping), in severe cases, shock and even instant death can occur.
Electrical burns are characterized by “current signs” - dense scabs at the site of contact of the skin with the wire. When struck by lightning, traces of the passage of current remain on the skin in the form of reddish poles - “lightning signs”. Ignition of clothing when exposed to current leads to burns.
· The main factor in damaging the body is the strength of the current flowing through the body. It is determined by Ohm's law, which means it depends on the applied voltage and resistance of the body. With a point contract, skin resistance is the determining factor that limits the current. Dry skin has a lot of resistance, while wet skin has little resistance. So, with dry skin, the resistance between the extreme points of the body, for example, from leg to arm or from one hand to the other, can be equal to 10 5 Ohms, and between sweaty hands it is 1500 Ohms.
Let's calculate the maximum currents that arise when contacting household appliances with mains voltage (220 V):
I1=2.2mA (dry skin);
I2=150mA (wet skin).
The brain, pectoral muscles and nerve centers that control breathing and heart function are most sensitive to electric current.
The passage of current through the human body can be clearly shown using such a model. A garland of light bulbs (for a Christmas tree) is inserted inside the human skeleton, passing through the organs that are most affected by electric shock.
· If current from an external source passes through the heart, uncoordinated contractions of its ventricles may occur. This effect is called ventricular fibrillation. Having arisen spontaneously, they do not stop, even if there is no current. The heart can be brought into this state with a current strength of 50 to 100 μA. The heart muscles, which do not receive blood for 1-2 minutes, weaken, as a result of which they cannot be brought back into a state of normal contractions. If emergency measures are taken before this point, the regular functioning of the heart can be restored.
Even weaker currents than those that cause ventricular fibrillation can lead to respiratory arrest, paralyzing the action of the nerve centers that control the functioning of the lungs. This condition persists even after the current is interrupted. Respiratory paralysis can occur with current levels ranging from 25 to 100 mA. Even at 10 mA, the pectoral muscles can contract so much that breathing stops. Some effects of current on the body are given in the following table:
Current strength | Effects of current |
Absent |
|
Loss of sensation |
|
Pain, muscle contractions |
|
Increasing impact on muscles, some damage |
|
Respiratory paralysis |
|
Ventricular fibrillation (immediate resuscitation required) |
|
Cardiac arrest (if the shock was brief, the heart can be resuscitated), severe burns |
Causes of electric shock
The main causes of electrical injuries:
1. Malfunction of devices or protective equipment
2. Short circuit of phase wires to ground.
irritability, pain in
heart area
III Conclusion
More and more electrical appliances are entering our everyday lives. But do they all improve our health? Not at all. The work of many of them makes work easier, creates comfort, but has a negative impact on human well-being. So quite often we pay for comfort with our health. The table shows the negative effects of some household appliances and possible measures to reduce this effect on our health.
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Household appliance
Danger factor
Electric shaver
High intensity electromagnetic field
Reduce its operating time, and it is better to use a mechanical razor
Microwave
Electromagnetic field
Do not go close to the oven when it is on
Electronic tube of a computer or TV
Electromagnetic field, x-ray radiation
Limit operating time, taking into account that radiation is maximum on the sides and behind these devices
Radiotelephone
Narrowband electromagnetic radiation
Talk less on it
Electric blanket
Electromagnetic field
Use only to warm the bed, but do not sleep under it
Sound engineering
Low frequency sounds, noises
Avoid loud sounding equipment
The following electric fields affect me:
Field Source | frequency Hz | Status (on or off) | Field strength, V/m |
|
At a distance of 0.5 m |
||||
Desk lamp | ||||
Desk lamp | ||||
On off. | ||||
Electric kettle | On off | |||
Be careful with electricity!
The passage of current through the human body with a force of about 100 mA causes serious damage to the body. A current of up to 1 mA is considered safe for humans. The resistivity of the top layer of dry human skin is very high. If the skin is not damaged and there is no moisture on it, then the resistance of the human body is very significant (15 kOhm). However, in a damp room, the resistance of the human body decreases sharply and voltages up to 12 V are considered safe. Remember that electrical installation and repair of the electrical circuit should be carried out only when the voltage is removed.
References.
1. Bludov in physics. – M.: Education, 1975.
2. Bogatyrev. – M.: 1983.
3. Gostyushin himself and loved ones. – M.: 1978.
4. Toporev life safety. 10 – 11 grade. – M.: Education, 2000.
5. Great Encyclopedia of Cyril and Methodius. 2001
ELECTRIC CHARGE, a quantity that determines the intensity of electromagnetic interaction of charged particles; source of electromagnetic field. The electric charge of any charged bodies is an integer multiple of the elementary electric charge e. The electric charges of the constituent hadrons - quarks - are fractional (multiples of 1/3 e). The total electrical charge of a closed system is conserved during all interactions
MAXWELL (Maxwell) James Clerk (June 13, 1831, Edinburgh, - November 5, 1879, Cambridge), English physicist, creator of classical electrodynamics, one of the founders of statistical physics, founder of one of the world's largest scientific centers of the late 19th century - early. 20th centuries - Cavendish Laboratory; created the theory of the electromagnetic field, predicted the existence of electromagnetic waves, put forward the idea of the electromagnetic nature of light, established the first statistical law - the law of the distribution of molecules by speed, named after him.
(/06), Russian physicist and electrical engineer, one of the pioneers of the use of electromagnetic waves for practical purposes (including for radio communications. In early 1895 he created a version of the radio receiver that was perfect for that time and demonstrated it 2, using it as a source of electromagnetic radiation Hertz vibrator. Based on his radio receiver, he designed (1895) a device for recording lightning discharges (“lightning detector”). In 1897, he began work on wireless telegraphy. In the same year, he transmitted his first radiogram, consisting of one word, over a distance of about 200 m. Hertz "In 1901 he achieved a radio communication range of about 150 km. Gold medal at the 1900 World Exhibition in Paris.
Guglielmo Marconi (Marconi), Italian radio engineer and entrepreneur. From 1894 in Italy, and from 1896 in Great Britain, he conducted experiments on the practical use of electromagnetic waves; in 1897 he received a patent for the invention of a method of wireless telegraphy. Organized a joint stock company (1897). Contributed to the development of radio as a means of communication. Nobel Prize (1909, jointly with).
Causes of electric shock Touching live parts that are energized; Touching disconnected parts of the equipment where voltage may occur: – in case of residual charge; – in case of erroneous switching on of the electrical installation or uncoordinated actions of the maintenance personnel; – in the event of a lightning discharge into or near an electrical installation; – touching metal non-current-carrying parts or electrical equipment associated with them (casings, casings, fences) after the voltage transfers to them from live parts (emergency situation occurs - breakdown on the casing). Injury from step voltage or the presence of a person in the field of spreading electric current in the event of a ground fault. Damage through an electric arc when the voltage of the electrical installation is higher than 1 kV, when approaching an unacceptably short distance. The effect of atmospheric electricity during lightning discharges. Freeing a person under tension.
Causes of electrical injuries A person cannot remotely determine whether the installation is energized or not. The current that flows through the human body affects the body not only at the points of contact and along the path of the current, but also on systems such as the circulatory, respiratory and cardiovascular systems. The possibility of electrical injury occurs not only through touch, but also through the voltage of a step.
The effect of electric current on the human body Electric current, flowing through the human body, produces thermal, electrolytic, biological, and mechanical effects. General electrical injuries include electric shock, in which the process of excitation of various muscle groups can lead to convulsions, cessation of breathing and cardiac activity. Cardiac arrest is associated with fibrillation - a chaotic contraction of individual fibers of the heart muscle (fibrils). Local electrical injuries include burns, electrical marks, metallization of the skin, mechanical damage, electroophthalmia (inflammation of the eyes as a result of exposure to ultraviolet rays of an electric arc).
The nature of the impact of currents on the human body: ~ 50 Hz constant 1. Non-releasing mA mA 2. Fibrillation 100 mA 300 mA 3. Sensible current 0.6-1.5 mA 5-7 mA 4. A current at which a person can independently free yourself from the electrical circuit
Maximum permissible levels (MPL) of touch voltages and current during emergency operation of electrical installations according to GOST: Type and frequency of currentNorm. Vel.PRU, at t, s 0.01 - 0.08 over 1 Variable f = 50 Hz UDIDUDID 650 V 36 V 6 mA Variable f = 400 Hz UDIDUDID 650 V 36 V 6 mA Constant UDIDUDID 650 V 40 V 15 mA
Classification of premises according to the danger of electric shock (PUE) Class I premises. Particularly dangerous premises. (100% humidity; presence of a chemically active environment or more than 2 factors, class 2) Class II premises. Premises with increased risk of electric shock. (one of the following factors is present: - increased air temperature (t = + 35 C); - increased humidity (> 75%)); - the presence of conductive dust; - the presence of conductive floors; - the possibility of touching both the electrical installation and to grounding or to two electrical installations at the same time. Class III premises. There are no signs characteristic of the two previous classes. 75%)); - presence of conductive dust; - presence of conductive floors; - possibility of touching the email at the same time. installation and to grounding or to two el. installations simultaneously. Class III premises. Few dangerous premises. There are no signs characteristic of the two previous classes."> 
Grounding resistance according to the PUE PUE: the grounding resistance should not exceed: in U installations 1000 V with an effectively grounded neutral (with low ground fault currents I of 1000 V with an isolated neutral - 250/Iz, but not more than 10 Ohms; in U installations > 1000 V with an insulated neutral, if the grounding device is simultaneously used for electrical installations with voltages up to 1000 V, - 125/Iz, but not more than 10 Ohms (or 4 Ohms, if required for installations up to 1000 V). 1000 V with an effectively grounded neutral (with low ground fault currents Iз 1000 V with an isolated neutral - 250/Iз, but not more than 10 Ohm; in installations U > 1000 V with an isolated neutral, if the grounding device is simultaneously used for electrical installations with voltages up to 1000 V, – 125/Iз, but not more than 10 Ohms (or 4 Ohms, if required for installations up to 1000 V)."> 
Grounding Grounding is intended to eliminate the danger of electric shock when there is a short circuit to the housing of electrical installations operating under voltage up to 1000 V in three-phase four-wire networks with a solidly grounded neutral. Grounding is the deliberate connection of metal non-current-carrying parts of equipment that may be energized with a neutral protective conductor. Grounding turns a breakdown on the housing into a short circuit and promotes the flow of high current through network protection devices and quickly disconnects damaged equipment from the network.
Protective equipment Basic insulating electrical protective equipment can withstand the operating voltage of an electrical installation for a long time. in electrical installations with voltages up to 1000 V - dielectric gloves, tools with insulating handles and voltage indicators up to 1000 V; electrical installations with voltages above 1000 V - insulating rods, insulating and electrical clamps, as well as voltage indicators above 1000 V. Additional insulating electrical protective equipment has insufficient electrical strength and cannot independently protect a person from electric shock. Their purpose is to enhance the protective effect of basic insulating agents. in electrical installations with voltages up to 1000 V - dielectric overshoes, mats and insulating stands; in electrical installations with voltages above 1000 V - dielectric gloves, boots, mats, insulating stands
Safety Posters and Signs Warning: Stop! Tension, don't get involved! Will kill, Test! Life threatening; Prohibiting: Do not turn on! People are working, don't turn it on! Work on the line, Do not open! People are working, work under tension! Do not turn it on again; Prescriptive: Work here, Climb here; Index: Grounded
