What is dangerous electricity? How electric current affects a person

Fact of action electric current per person was established in the last quarter of the 18th century. The danger of this action was first established by the inventor of the electrochemical high-voltage voltage source VV Petrov. The description of the first industrial electrical injuries appeared much later: in 1863 - from direct current and in 1882 - from alternating current.

Electric current, electrical injuries and electrical injuries

Electrical injury refers to injury caused by electric current or electric arc.

Electrical injury characterize the following features: a protective reaction of the body appears only after a person is under voltage, that is, when an electric current is already flowing through his body; electric current acts not only at the points of contact with the human body and on the way through the body, but also causes a reflex effect, manifested in a violation of the normal activity of the cardiovascular and nervous system, breathing, etc. A person can get an electrical injury both by direct contact with live parts, and by being struck by a touch or step voltage, through an electric arc.

Electrical injury in comparison with other types of industrial injuries is a small percentage, however, in terms of the number of injuries with a severe, and especially fatal, outcome, it occupies one of the first places. Largest number electrical injuries (60-70%) occur when working on electrical installations with voltages up to 1000 V. This is due to the wide distribution of such electrical installations and the relatively low level of electrical training of persons operating them. There are much fewer electrical installations with a voltage of over 1000 V in operation, and they are served, which causes a smaller number of electrical injuries.

The causes of electric shock to a person are as follows: touching uninsulated live parts; to metal parts of the equipment that are energized due to damage to the insulation; to non-metallic objects that are energized; shock voltage step and through the arc.

Types of human electric shock

Electricity, flowing through the human body, affects it thermally, electrolytically and biologically. Thermal action is characterized by heating of tissues, up to burns; electrolytic - decomposition of organic liquids, including blood; the biological effect of electric current is manifested in the violation of bioelectric processes and is accompanied by irritation and excitation of living tissues and muscle contraction.

There are two types of electric shock to the body: electrical trauma and electrical shock.

electrical injury- these are local lesions of tissues and organs: electrical burns, electrical signs and electroplating of the skin.

electrical burns arise as a result of heating human tissues by an electric current flowing through it with a power of more than 1 A. Burns can be superficial when the skin is affected, and internal - when deep-lying tissues of the body are damaged. According to the conditions of occurrence, contact, arc and mixed burns are distinguished.

electrical signs are spots of gray or pale yellow color in the form of calluses on the surface of the skin at the point of contact with current-carrying parts. Electrical signs are usually painless and go away over time.

Skin electroplating- this is the impregnation of the surface of the skin with metal particles when it is sprayed or evaporated under the influence of an electric current. The affected area of ​​the skin has a rough surface, the color of which is determined by the color of the metal compounds that have fallen on the skin. Electroplating of the skin is not dangerous and disappears over time, as do electrical signs. Metallization of the eyes is a great danger.

Electrical injuries also include mechanical damage as a result of involuntary convulsive muscle contractions during the flow of current (ruptures of the skin, blood vessels and nerves, dislocations of joints, bone fractures), as well as electrophthalmia- inflammation of the eyes as a result of the action of ultraviolet rays of an electric arc.

electric shock is the excitation of living tissues by electric current, accompanied by involuntary convulsive muscle contraction. According to the outcome, electric shocks are conditionally divided into five groups: without loss of consciousness; with loss of consciousness, but without disturbance of cardiac activity and respiration; with loss of consciousness and impaired cardiac activity or breathing; clinical death and electric shock.

Clinical or "imaginary" death It is a transitional state from life to death. Able clinical death cardiac activity stops and breathing stops. Duration of clinical death 6...8 min. After this time, the cells of the cerebral cortex die, life fades away and irreversible biological death occurs. Signs of clinical death: cardiac arrest or fibrillation (and, as a result, no pulse), no breathing, bluish skin, pupils of the eyes are sharply dilated due to oxygen starvation of the cerebral cortex and do not react to light.

electric shock- this is a severe neuroreflex reaction of the body to irritation with an electric current. With shock, deep disorders of respiration, blood circulation, the nervous system and other body systems occur. Immediately after the action of the current, the phase of excitation of the body begins: a reaction to pain appears, increases arterial pressure and others. Then comes the phase of inhibition: the nervous system is depleted, blood pressure decreases, breathing weakens, the pulse drops and quickens, a state of depression occurs. A state of shock can last from several tens of minutes to a day, and then recovery or biological death may occur.

Electric current thresholds

An electric current of different strength has a different effect on a person. Threshold values ​​of electric current are distinguished: threshold perceptible current - 0.6...1.5 mA at alternating current with a frequency of 50 Hz and 5...7 mA at direct current; threshold non-release current (current that, when passing through a person, causes irresistible convulsive contractions of the muscles of the hand in which the conductor is clamped) - 10 ... 15 mA at 50 Hz and 50 ... 80 mA at direct current; threshold fibrillation current (current that causes fibrillation of the heart when passing through the body) - 100 mA at 50 Hz and 300 mA at direct electric current.

What determines the degree of action of electric current on the human body

The outcome of the lesion also depends on the duration of the current flow through the person. With an increase in the duration of a person's stay under voltage, this danger increases.

The individual characteristics of the human body significantly affect the outcome of damage in electrical injuries. For example, a non-letting current for some people can be a threshold perceptible for others. The nature of the current of the same force depends on the mass of a person and his physical development. It has been established that for women the threshold current values ​​are about 1.5 times lower than for men.

The degree of action of the current depends on the state of the nervous system and the whole organism. So, in a state of excitation of the nervous system, depression, illness (especially diseases of the skin, cardiovascular system, nervous system, etc.) and intoxication, people are more sensitive to the current flowing through them.

The “attention factor” also plays a significant role. If a person is prepared for an electric shock, then the degree of danger is sharply reduced, while an unexpected shock leads to more serious consequences.

The current path through the human body significantly affects the outcome of the lesion. The danger of defeat is especially great if the current, passing through the vital organs - the heart, lungs, brain - acts directly on these organs. If the current does not pass through these organs, then its effect on them is only reflex and the probability of injury is less. The most common current paths through a person, the so-called "current loops", have been established. In most cases, the current circuit through a person occurs along the path of the right arm - legs. However, disability for more than three working days is caused by the flow of current along the path arm - arm - 40%, the current path right arm - legs - 20%, left arm - legs - 17%, other paths are less common.

What is more dangerous - alternating or direct electric current?

The danger of alternating current depends on the frequency of this current. Studies have found that currents in the range from 10 to 500 Hz are almost equally dangerous. With a further increase in the frequency, the values ​​of the threshold currents increase. A noticeable decrease in the risk of electric shock to a person is observed at frequencies above 1000 Hz.

Direct current is less dangerous and its threshold values ​​are 3 - 4 times higher than alternating current with a frequency of 50 Hz. However, when the DC circuit breaks below the threshold perceptible, sharp pain sensations arise, caused by the transient current. The statement about the lower danger of direct current compared to alternating current is valid at voltages up to 400 V. In the range of 400 ... 600 V, the dangers of direct and alternating currents with a frequency of 50 Hz are almost the same, and with a further increase in voltage, the relative danger of direct current increases. This is explained physiological processes action on living cells.

Consequently, the effect of electric current on the human body is diverse and depends on many factors.

Chapter 14

FROM THE ACTION OF ELECTRIC CURRENT

ELECTRIC SHOCK HAZARD

The effect of electric current on the human body. Electric current is currently used in all areas of human activity: production, everyday life, medicine, etc., as an energy source that is convenient to transport and use. With all the advantages of using electricity, the danger of electricity to humans cannot be ignored.

The effect of electric current on living tissue, unlike other factors, is unique and versatile. Passing through the body, the electric current produces thermal, electrolytic, mechanical (dynamic) and biological effects.

thermal action manifests itself in the heating of tissues up to burns of individual parts of the body, heating to a high temperature of blood vessels, nerves, heart, brain and other organs that are on the path of the current, which causes serious functional disorders in them.

Electrolytic action causes decomposition of blood and plasma, which is accompanied by significant violations of their physical and chemical composition.

Mechanical (dynamic) action current is expressed in stratification, rupture and other similar damage to various tissues of the body: muscle tissue, walls of blood vessels, vessels of the lung tissue.

Biological action It is expressed in irritation and excitation of the living tissues of the body, which may be accompanied by involuntary convulsive muscle contractions, including the muscles of the heart and lungs, as well as in violation of internal bioelectrical processes that occur in a normally functioning organism and are closely related to its vital functions.

These actions are conditionally reduced to two main types of injuries: local electrical injuries and electric shocks.

Local electrical injuries - these are clearly defined local violations of the integrity of body tissues caused by exposure to electric current or an electric arc. Characteristic species local electrical injuries - electrical burns, electrical signs and marks, skin metallization, electrophthalmia and mechanical damage.

Electric shock - This is the excitation of living tissues of the body by an electric current passing through it. It can cause convulsive contraction of muscles without loss of consciousness, with loss of consciousness, without damage or with damage to the work of the heart and respiratory system, as well as clinical death. Clinical or imaginary death - a short-term transitional state from life to death, occurring from the moment the activity of the heart and lungs ceases. The signs of clinical death are as follows: cardiac arrest and, as a result, the absence of a pulse, lack of breathing, the skin is bluish-pale, the pupils of the eyes are sharply dilated (due to oxygen starvation of the cerebral cortex) and do not react to light, pain irritations do not cause any reactions in the victim. The duration of clinical death is determined by the time from the moment of cessation of cardiac activity and respiration until the onset of death of the cells of the cerebral cortex; in most cases it is 4 - 5 minutes.

Factors that determine the outcome of electric shock. In general, the degree of electric shock is determined by the amount of absorbed electrical energy in organs, tissues and systems when an electrical circuit occurs through the human body.

The nature of the impact and the severity of human injury depends on many interrelated factors, such as the strength of the current, the duration of the current, the resistance of the human body, the path of passage, the type (constant, rectified, variable) and frequency of the current, the “attention factor”, the individual properties of the victim and factors environment.

With the increase current strength three qualitatively different responses of the body are clearly manifested: an unpleasant sensation, convulsive contraction of the muscles and fibrillation of the heart. Electric currents that cause an appropriate reaction are divided into tangible, non-release and fibrillation, and their minimum values ​​are usually called threshold.

as show experimental studies, a person begins to feel the flow of an alternating current with a frequency of 50 Hz through him with a power of the order of 0.6 - 1.5 mA. A perceptible current does not cause disturbances in the body's activity, therefore, its long-term flow through the human body under production conditions is permissible.

If a person who has been energized is able to independently overcome the effect of convulsions and free himself from contact with conductors, then such a current is called releasing. In cases where a person cannot free himself from contact, there is a danger of prolonged convulsions. The currents that cause such a reaction of the body are called non-letting currents. The threshold values ​​of non-releasing alternating currents at a frequency of 50 Hz lie within 10 - 15 mA. At 25–50 mA, the action of the current also extends to the muscles of the chest, which leads to difficulty and even cessation of breathing. When exposed to this current for several minutes, death may occur due to the cessation of lung function. There is a dependence of the threshold non-release currents on the weight of a person and his age. So, with an increase in weight from 50 to 80 kg, the value of the threshold current increases by 1.4 - 2 times.

A current of 50–80 mA affects the respiratory and cardiovascular systems. At 100 mA for 2–3 seconds, cardiac fibrillation occurs, which consists in random chaotic contraction and relaxation of the muscle fibers of the heart (fibrils). It stops, circulation stops. This current is called fibrillation.

Duration of current flow Through the human body, it affects the resistance of the skin, as a result of which, with an increase in the time of current exposure to living tissue, its value increases, and the consequences of current exposure to the body increase.

Permissible currents for a person are evaluated according to three electrical safety criteria. First criterion - a perceptible current that does not cause disturbances in the activity of the body and is allowed for a long (no more than 10 minutes per day) flow through the human body in the normal (non-emergency) mode of the electrical installation. For alternating current with a frequency of 50 Hz, its strength is 0.3 mA, and for direct - 1 mA. The releasing current is taken as the second criterion. Its effect on a person is permissible with a duration of more than 1 second. The release current for AC is 6 mA, for DC - 15 mA. The third criterion is the fibrillation current, which does not exceed the threshold fibrillation current and is short-term (up to 1 s). The maximum allowable values ​​of alternating currents with a frequency of 50 Hz and contact voltages during emergency operation of industrial electrical installations with voltage up to 1000 V, depending on the duration of exposure, should not exceed the values ​​\u200b\u200bspecified in GOST 12.1.038-82 as amended. dated 01.07.88 and given in Table 14.1.

Table 14.1

Maximum permissible values ​​of contact voltage U etc. and currents I h,

flowing through the human body, in emergency mode

industrial electrical installations with voltage up to 1000 V

t, With		Duration of current exposure t, With	Maximum permissible values, no more
U pr, V	I h, mA	U pr, V	I h, mA
0,01-0,08			0,6
0,1			0,7
0,2			0,8
0,3			0,9
0,4			1,0
0,5			Over 1.0

Knowledge of the norms for permissible values ​​of contact voltage and currents through the human body is necessary when developing methods and means of protecting people, when assessing electrical safety conditions in existing electrical installations, and when investigating electrical injuries.

Electrical resistance of the human body is variable, depending on the touch voltage, on the condition of the skin, the parameters of the electrical circuit, physiological factors and the state of the environment.

The total electrical resistance of the human body has active and capacitive components and consists of the resistance of the skin and the resistance of internal tissues.

The upper layer of the skin, called the epidermis, and consisting mainly of dead keratinized cells, has a high resistance, which determines the overall resistance of the human body. The resistance of the lower layers (dermis) and internal human tissues is insignificant (300–500 ohms). With dry, clean and intact skin, the resistance of the human body, measured at voltages up to 15–20 V, ranges from (3–100) × 10 3 Ohm. When moistened, as well as when it is damaged (under the contacts), the resistance of the body turns out to be the smallest - about 500 Ohm, i.e. reaches a value equal to the resistance of the internal tissues of the body. For approximate calculations, the resistance of the human body is considered purely active and equal to 1 kOhm at touch voltages above 50 V, 6 kOhm at touch voltages less than 50 V.

The inclusion of vital organs of a person in the zone of action of the current increases the possibility of a severe outcome. The most dangerous are loops when the brain and spinal cord are in the current circuit. A fatal outcome is possible even at low voltages (12 V), if the current passes through the biologically active points of the body on the neck, temples, lower leg, shoulders, back and other places of the human body.

At voltages up to 500 V, it is more dangerous alternating current, with a further increase in voltage, the danger of direct current increases rapidly.

When the frequency of the alternating current changes from zero to 100 Hz, the danger of injury at the same voltage increases, reaching a maximum in the range of 50 - 60 Hz, at a frequency of 200 Hz, the risk of fibrillation is reduced by 2 times, at a frequency of 400 Hz - more than 3 times.

Currents above 500,000 Hz do not cause electric shock, but they can cause thermal burns.

The physical and psychological state of a person has a certain influence on the outcome of the lesion. Fatigue, depressed mental condition, alcohol consumption, a number of diseases increase the risk of exposure to electric current. Therefore, a list of diseases has been defined, in the presence of which work in existing electrical installations is not allowed. Maintenance of electrical installations is entrusted to employees who have undergone a medical examination and special education. Of great importance is the "attention factor", which reduces the danger of current.

In general, people in the room are less at risk. However, if this is a production room, then the presence of dampness, conductive dust, many types of electrical equipment, and aggressive environments increase the risk of electric shock.

Classification of premises according to the danger of electric shock. In accordance with the Electrical Installation Rules (PUE), all premises are divided into three classes in relation to the danger of electric shock to people: without increased danger, with increased danger, especially dangerous.

Premises without increased danger - these are dry, dust-free rooms with normal air temperature and with insulating (for example, wooden) floors, i.e. in which there are no conditions that create an increased or special danger. Such premises include office premises, tool rooms, laboratories, etc.

High risk areas characterized by the presence in them of one of the following conditions that create an increased danger: dampness (relative humidity exceeds 75% for a long time) or conductive dust (coal, metal, etc.); conductive floors (metal, earthen, reinforced concrete, brick, etc.); high temperature (air temperature above +35 C); the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological devices, mechanisms, etc., on the one hand, and to the metal cases of electrical equipment - with another.

Examples of premises with increased danger are stairwells of buildings with conductive floors, storage rooms that are not heated, etc.

Particularly dangerous premises, characterized by the presence of one of the following conditions that create a particular danger: extreme dampness (relative humidity close to 100%); chemically active or organic environment that destroys insulation and current-carrying parts of electrical equipment; two or more high-risk conditions at the same time.

Particularly dangerous premises are most of the industrial premises, including all equipment repair shops, workshops, etc.

Territories of location of outdoor electrical installations (in the open air or under a canopy) in relation to the danger of electric shock to people are equated to especially dangerous premises

Before proceeding to independent work connected with electricity in your apartment or in a private house, you need to know that these works are very dangerous.

For a person, the voltage, which is already dangerous for his life, starts from 25 V.

As you know, electric current is invisible, inaudible and odorless. However, for all its invisibility, electricity makes the electrical appliances that light and heat houses work. But this energy can easily go from creative to destructive and even deadly.

What is the danger of electric contact with a person? There are two main reasons:

• the first is a mechanical damage to human tissues;
• the second is the effect of electricity on the nervous system.

As is known, in humans, the mechanism of transmission of nerve signals is based on an electrochemical nature. Simply put, a person has his own electricity. With the help of nerve signals, the muscles move, including the heart, coordination and control of all internal organs are carried out. In the case of contact with an energized conductor, the human body reacts to this as a signal of its own nervous system, but much more powerfully. The muscles convulsively contract, coming into a state of constant tension, and it is not possible to relax them, since the incoming signal from the outside far exceeds the commands of the body itself.

Everybody knows Golden Rule electricians - touch the bare conductors with the back of the hand so that the muscles of the hand, having received an electric shock, clench the hand into a fist, thereby pushing the hand away from the contact. Otherwise, the palm will tightly clasp the conductor and it will be impossible to unclench it. A person will be under continuous current, which is very dangerous. With a particularly strong influence of current, dislocations, ruptures of ligaments and even bone fractures are possible, caused by powerful muscle contractions.

Voltage from 25 V is considered dangerous for a person. In this situation, it is necessary to clearly distinguish between voltage and current strength. It is strength that kills. For example: blue sparks of static discharges have a voltage of 7000 V, but negligible power, while the voltage in the outlet is 220 V. But with a current of 10-16 A, it can cause death. Moreover, the passage of a current with a force of 30-50 mA through the heart muscle can already cause fibrillation (flutter) of the heart muscle and reflex cardiac arrest.

How this will end is quite clear. If the current does not touch the heart (and the path of electricity in human body are very bizarre), then its effect can cause paralysis of the respiratory muscles, which also does not bode well. There were absolutely amazing incidents when an electric current, without leaving visible damage, literally roasted the internal organs, bringing them to a boil.

Mechanical damage to body tissues is divided into physical and chemical effects.

physical impact

This is primarily a thermal injury. The generation of heat during the passage of electric current through a conductor (in this case, the human body) depends on the resistance of this conductor. This value for dry human skin is approximately 1000 ohms, which is quite enough for burns of varying severity (this, of course, depends on the strength of the current and does not mean that electrical contact with wet skin is preferable).

The resistance drops sharply, and the electric discharge penetrates the human body further, affecting the internal organs more strongly.

Physical impact also includes damage to the eyes during flashes of an electric arc or short circuit. Harsh ultraviolet light can seriously burn the retina, causing temporary or permanent blindness, color vision inversion, etc.

Chemical exposure

When a discharge passes through human tissues, the current changes the electrolytic properties of tissue fluid, blood, lymph, etc. This is fraught with serious consequences, since the composition of the blood is unchanged and must remain so. A shift in acidity, erythrocyte properties and chemical composition can cause severe damage to the body.

As can be seen from the foregoing, almost any contact with electricity, if not fatal, is very unpleasant. The degree of damage depends on the strength of the current and the time of exposure to the human body. It is far from always that the passage of a discharge through the human body causes such serious consequences. According to statistics, for every 120-140 thousand cases of contact with electricity, only one ends in death.

Much more often there are situations when contact leads to injuries of varying severity. However, this is not a reason to treat electricity carelessly. Especially where a person often comes into contact with him: during electrical work or repairs. To minimize the risk of electric shock, it is necessary to thoroughly study the basic safety rules and apply protective equipment.

Almost all workplaces where there is electrical equipment (portable electrical receivers) under voltage are considered dangerous. In each such place, the danger of electric shock to a person cannot be considered excluded. Approximately 70% of accidents involving electric shock occur during professional activity victims. According to long-term statistical data, electrical injuries account for about 2% in total occupational injuries, and about 20% in fatal ones.

ACTION OF ELECTRIC CURRENT ON A HUMAN

The human body is a conductor of electric current. Electric current has significant features that distinguish it from other harmful and dangerous production factors.

The first feature of the electric current is that it does not have color, smell, sound, and therefore a person cannot determine the presence of an electric current with the help of his own senses.

The second feature of the electric current is that you can get an electrical injury without direct contact with live parts (for example, when moving along the ground (conductive floor) near a damaged electrical installation, power receiver (in the event of a ground fault, floor), as well as through an electric arc, discharge lightning

The third feature of the electric current is that, passing through the human body, the electric current exerts its effect not only at the points of contact and on the way through the body, but also causes a reflex effect, disrupting the normal activity of individual organs and systems of the human body (nervous, cardiovascular vasculature, respiratory organs, etc.)

Electric current, passing through the human body, has a biological, electrochemical, thermal and mechanical effect.

biological the action of the current is manifested in irritation and excitation of tissues and organs. As a result, skeletal muscle spasms are observed, which can lead to respiratory arrest, avulsion fractures, dislocations of the limbs, spasm of the vocal cords.

electrolytic the action of the current is manifested in the electrolysis (decomposition) of liquids, including blood, and also significantly changes the functional state of cells.

thermal the action leads to burns of the skin, as well as the death of underlying tissues, up to charring.

mechanical the action of the current is manifested in the stratification of tissues and even the separation of parts of the body.

Typical types of local electrical injuries are electrical burns, electrical signs, skin plating, electrophthalmia and mechanical damage.

The most common electrical injury is electrical burns. According to the depth of the lesion, all burns are divided into four degrees:

The first is redness and swelling of the skin;

The second is water bubbles;

The third is the necrosis of the superficial and deep layers of the skin;

Fourth - charring of the skin, damage to muscles, tendons and bones.

Metallization of the skin - the penetration into its particles of metal, melted under the action of an electric arc.

Electrophthalmia - inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet rays. Occurs most often during electrical welding work.

Mechanical damage occurs as a result of sharp, involuntary, convulsive muscle contractions under the influence of current passing through the human body. In this case, ruptures of the skin, blood vessels and nervous tissue are possible, as well as dislocations of the joints and bone fractures.

electric shock

The variety of action of electric current on the body leads to various electrical injuries. Conventionally, all electrical injuries can be divided into local and general.

TO local electrical injuries include local damage to the body or pronounced local violations of the integrity of body tissues, including bone tissue, caused by exposure to electric current or an electric arc.

The most typical local injuries include electrical burns, electrical signs, skin plating, mechanical damage, and electrophthalmia.

Electric burn (integumentary) occurs, as a rule, in electrical installations up to 1000 V. At higher voltages, an electric arc or spark occurs, which causes an electric arc burn.

current burn part of the body is a consequence of the conversion of the energy of the electric current passing through this area into heat. This burn is determined by the magnitude of the current, the time of its passage and the resistance of the part of the body that has been exposed to the current. Maximum amount heat is released at the point of contact of the conductor with the skin. Therefore, basically, the current burn is a skin burn. However, electric burns can also damage subcutaneous tissues. At high frequency currents, internal organs are most susceptible to current burns.

An electric arc causes extensive burns to the human body. In this case, the defeat is severe and often ends in the death of the victim.

electrical signs current impacts are sharply defined spots of gray or pale yellow color on the surface of the human body. Usually they have a round or oval shape and dimensions of 1-5 mm with a depression in the center. The affected area of ​​the skin hardens like a callus. There is necrosis of the upper layer of the skin. The surface of the sign is dry, not inflamed. Electrical signs are painless. Over time, the top layer of the skin comes off and the affected area acquires its original color, elasticity and sensitivity.

Leather plating- penetration into the upper layers of the skin of particles of metal melted under the action of an electric arc. Such cases occur during short circuits, disconnection of circuit breakers under load. In this case, splashes of molten metal under the action of the resulting dynamic forces and heat flow scatter in all directions at high speed. Since the melted particles have a high temperature, but a small supply of heat, they are not able to burn through clothes and affect the usually open parts of the body - the face, hands.

The affected area of ​​the skin has a rough surface. The victim feels pain from burns on the affected area and experiences skin tension from the presence of a foreign body in it. Eye damage by molten metal is especially dangerous. Therefore, work such as removing and replacing fuses must be carried out while wearing protective goggles.

With direct current, metallization of the skin is also possible as a result of electrolysis, which occurs with close and relatively long contact with a current-carrying part that is energized. In this case, metal particles are introduced into the skin by an electric current, which simultaneously decomposes the organic fluid in the tissues and forms basic and acid ions in it.

Mechanical damage are the result of sharp involuntary convulsive muscle contractions under the influence of current passing through the human body. As a result, ruptures of tendons, skin, blood vessels and nervous tissue can occur. Joint dislocations and even bone fractures may also occur. Mechanical damage caused by convulsive muscle contraction occurs mainly in installations up to 1000 V when a person is under voltage for a long time.

Electrophthalmia occurs as a result of exposure to a stream of ultraviolet rays (electric arc) on the membrane of the eyes, as a result of which their outer membrane becomes inflamed. Electrophthalmia develops 4-8 hours after exposure. In this case, there is redness and inflammation of the skin of the face and mucous membranes of the eyelids, lacrimation, purulent discharge from the eyes, spasms of the eyelids and partial loss of vision. The victim experiences a headache and a sharp pain in the eyes, aggravated by the light. In severe cases, the transparency of the cornea is impaired. Prevention of electrophthalmia during the maintenance of electrical installations is ensured by the use of goggles or shields with ordinary glass.

General electrical injuries arise when the living tissues of the body are excited by an electric current flowing through it and manifest themselves in involuntary convulsive contraction of the muscles of the body. At the same time, the entire body is under threat of damage due to disruption of the normal functioning of its various organs and systems, including the heart, lungs, central nervous system, etc. Common electrical injuries include electric shocks.

electric shock- this is the excitation of body tissues by an electric current passing through it, accompanied by muscle contraction.

Depending on the outcome of the impact of current on the human body, electric shocks can be divided into the following five degrees:

I - convulsive, barely perceptible muscle contraction;

II - convulsive muscle contraction, accompanied by severe pain, without loss of consciousness;

III - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;

IV - loss of consciousness and impaired cardiac activity and respiration;

V - lack of breathing and cardiac arrest (clinical death).

An electric shock may not lead to the death of a person, but cause such disorders in the body that may appear after a few hours or days (appearance of cardiac arrhythmia, angina pectoris, absent-mindedness, weakening of memory and attention).

There are two main stages of death: clinical and biological.

clinical death (sudden death)- a short-term transitional state from life to death, occurring from the moment of cessation of the activity of the heart and lungs. A person who is in a state of clinical death lacks all signs of life: there is no breathing, the heart does not work, painful stimuli do not cause a reaction of the body, the pupils of the eyes are sharply dilated and do not react to light. However, during this period, life in the body has not yet completely died out; tissues and cells do not immediately undergo decay, and remain viable. The brain cells that are very sensitive to oxygen starvation are the first to die. After some time (4-6 minutes) there is a multiple decay of brain cells, which leads to irreversible destruction and virtually eliminates the possibility of reviving the body. However, if before the end of this period the first medical aid is provided to the victim, then the development of death can be stopped and the life of a person can be saved.

biological death- an irreversible phenomenon, which is characterized by the cessation biological processes in the cells and tissues of the body and the breakdown of protein structures. Biological death occurs after clinical death (7-8 minutes).

The causes of death from electric current can be: cessation of the heart, respiratory arrest and electric shock.

The effect of current on the heart muscle can be direct, when the current passes directly through the region of the heart, and reflex, that is, through the central nervous system. In both cases, cardiac arrest or fibrillation may occur. Cardiac fibrillation is a chaotic contraction of the fibers of the heart muscle at different times, in which the heart is not able to drive blood through the vessels. Currents less than 50 mA and more than 5 A at a frequency of 50 Hz, as a rule, do not cause cardiac fibrillation.

The cessation of breathing usually occurs as a result of the direct effect of the current on the muscles of the chest involved in the breathing process.

electric shock- a kind of severe neuro-reflex reaction of the body in response to excessive irritation with an electric current, accompanied by deep disorders of blood circulation, respiration, metabolism, etc. In shock, immediately after exposure to an electric current, the victim enters a short-term phase of excitation, when he reacts sharply to the pain that has arisen, his blood pressure rises. This is followed by a phase of inhibition and exhaustion of the nervous system, when blood pressure drops sharply, the pulse drops and quickens, breathing weakens, and depression occurs. The state of shock lasts from several tens of minutes to a day. After that, either death of a person or recovery can occur, as a result of active therapeutic intervention.

The outcome of the impact of current on the human body depends on the value and duration of the passage of current through his body, the type and frequency of the current, the individual properties of a person, his psychophysiological state, the resistance of the human body, voltage and other factors.

FACTORS THAT AFFECT THE DEGREE OF ELECTRIC SHOCK

The severity of electric shock depends on a number of factors: the magnitude of the force, the type (genus) and frequency of the electric current, the duration of its exposure and the path of passage through the person, environmental conditions, electrical resistance human body and its individual properties.

Current strength

To characterize the impact of electric current on a person, three criteria have been established:

Threshold perceptible current - smallest value the strength of an electric current that causes tangible irritations when passing through the human body. A person begins to feel a current of small value (0.6-1.5 mA at alternating current with a frequency of 50 Hz and 5-7 mA at direct current) - there is a slight trembling of the hands;

Threshold non-letting current - the smallest value of the electric current strength (10-15 mA at a frequency of 50 Hz and 50-80 mA at direct current), at which a person is not able to overcome muscle cramps and cannot unclench the hand in which the conductor is clamped, or violate contact with a live part;

Threshold fibrillation current - the smallest value of the current strength (from 100 mA to 5 A at a frequency of 50 Hz and from 300 mA to 5 A at direct current), causing fibrillation of the heart when passing through the human body - chaotic and multi-temporal contractions of the fibers of the heart muscle, which can cause it to stop

Type of current

The maximum permissible value of direct current is 3-4 times higher than the permissible value of alternating current, but only at voltages not higher than 260-300 V. At high voltages, direct current is more dangerous for humans due to its electrolytic action; it also affects the human heart.

Electric current frequency

The frequency of electric current (50 Hz) accepted in the energy sector poses a great danger of convulsions and ventricular fibrillation. Fibrillation is not a muscular response, but is caused by repeated stimulation with maximum sensitivity at 10 Hz. In addition, the production uses an electric current of other (not 50 Hz) frequencies. The danger of the action of the current decreases with increasing frequency, but this does not mean that the current with a frequency of 500 Hz is less dangerous than 50 Hz.

Current duration

The severity of the injury depends on the duration of the electric current. The time of passage of the electric current is critical in determining the extent of injury.

With prolonged exposure to electric current, the resistance of the skin (due to sweating) decreases at the points of contact and internal organs due to electrical processes, and the likelihood of current passing during a particularly dangerous period of the cardiac cycle (phase T of relaxation of the heart muscle) increases. A person can withstand a deadly alternating current of 100 mA if the duration of the current does not exceed 0.5 s.

The path of electric current through the human body

The most important condition for electric shock to a person is the path of this current. If vital organs (heart, lungs, brain) are in the path of the current, then the danger of fatal injury is very high. If the current passes in other ways, then its effect on the vital organs can only be a reflex. In this case, the danger of fatal injury, although it remains, but its probability is sharply reduced.

There are an innumerable number of possible ways for the passage of current in the human body. However, the following are typical:

hand - hand;

hand leg;

leg - leg;

head - hand;

head - leg.

The most dangerous are the “head-arm” and “head-leg” loops, when the current can pass not only through the heart, but also through the brain and spinal cord.

human body resistance

The electrical conductivity of various tissues of the body is not the same. Cerebrospinal fluid, blood serum and lymph have the highest electrical conductivity, followed by whole blood and muscle tissue. The internal organs, which have a dense protein base, brain substance and adipose tissue, conduct electrical current poorly. The skin and, mainly, its upper layer (epidermis) has the greatest resistance.

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. This is due to the thickness and degree of coarsening of the upper layer of the skin.

Areas of the body with the least resistance (i.e. more vulnerable):

Lateral surfaces of the neck, temples;

The back of the hand, the surface of the palm between the thumb and forefinger;

Hand in the area above the hand:

Shoulder, back;

Front leg:

Acupuncture points located in different parts of the body.

The current at which a person can independently free himself from the electrical circuit should be considered acceptable. Its value depends on the rate of passage of current through the human body: with a duration of more than 10 s - 2 mA, and for 120 s or less - 6 mA.

The safe voltage is considered to be 36 V (for lamps of local stationary lighting, portable lamps, etc.) and 12 V (for portable lamps when working inside metal tanks, boilers). But under certain situations, even such voltages can be dangerous.

Safe voltage levels are obtained from the lighting network using step-down transformers. It is impossible to extend the use of safe voltage to all electrical devices.

Two types of current are used in production processes - direct and alternating. They have different effects on the body at voltages up to 500 V. The danger of injury from direct current is less than alternating current. The greatest danger is the current with a frequency of 50 Hz, which is standard for domestic electrical networks.

The path along which the electric current passes through the human body largely determines the degree of damage to the body. The following options for the directions of current flow through the human body are possible:

• - a person touches current-carrying wires (parts of equipment) with both hands, in this case there is a direction of current flow from one hand to the other, i.e. “hand-hand”, this loop is most common;
• - when touching with one hand to the source, the current path closes through both legs to the ground “arm-legs”;
• - in the event of a breakdown of the insulation of the current-carrying parts of the equipment, the hands of the worker are energized on the case, at the same time, the flow of current from the equipment case to the ground leads to the fact that the legs are energized, but with a different potential, this is how the “hands-feet” current path arises ;
• - when current drains to earth from faulty equipment, the earth nearby receives a changing voltage potential, and a person who stepped on such earth with both feet finds himself under a potential difference, i.e. each of these feet receives a different voltage potential, as a result, a step voltage arises and the leg-to-leg electrical circuit, which happens the least and is considered the least dangerous;
• - touching the head to the current-carrying parts can cause, depending on the nature of the work performed, the current path to the arms or legs - “head-arms”, “head-legs”.

All options differ in the degree of danger. The most dangerous are the options “head-arms”, “head-legs”, “arms-legs” (full loop). This is due to the fact that the vital systems of the body - the brain, the heart - fall into the affected area.

The duration of current exposure affects the final outcome of the lesion. The longer the electric current acts on the body, the more severe the consequences.

Conditions external environment, human environment in the course of work activities may increase the risk of electric shock. High temperature and humidity, metal or other conductive floor increase the risk of electric shock.

According to the degree of danger of electric shock to a person, all premises are divided into three classes: without increased danger, with increased danger, especially dangerous.

The nature of the impact of alternating and direct current on the human body is presented in table 1.

Table 1 - The nature of the impact of alternating and direct current on the human body

Meaning	The nature of the impact
	AC 50 Hz	D.C
	The beginning of the sensation is a slight itching, tingling of the skin under the electrodes	Not felt
	The sensation of current extends to the wrist, slightly reduces the hand	Not felt
	Pain intensifies in the entire hand, accompanied by convulsions. Hands can usually be taken off the electrodes	The beginning of the feeling. The impression of heating the skin under the electrode
	Violent pains and cramps in the whole arm, including the forearm. Hands are difficult to take off the electrodes	Increased feeling of warmth
	Hardly bearable pains in the whole arm. Hands cannot be torn off from the electrodes.	Increased feeling of warmth
	Hands are paralyzed instantly, it is impossible to tear yourself away from the electrodes. Severe pain, difficulty breathing	An even greater increase in the sensation of heating the skin.
	Very severe pain in arms and chest. Breathing is extremely difficult. With prolonged current, respiratory paralysis or weakening of the heart's activity with loss of consciousness may occur.	Sensation of intense heat, pain and cramps in the arms. When the hands are separated from the electrodes, hardly tolerable pain occurs as a result of convulsive muscle contraction.
	Breathing is paralyzed after a few seconds, the work of the heart is disrupted. With prolonged current flow, cardiac fibrillation may occur.	Sensation of very strong superficial and internal heating, severe pains in the whole arm and in the chest. Difficulty breathing. Hands cannot be torn off the electrodes due to severe pain when contact is broken
	Fibrillation of the heart after 2-3 s; a few seconds later - heart failure	Respiratory paralysis with prolonged current flow
	Same action in less time	Fibrillation of the heart after 2-3 s; a few seconds later - respiratory paralysis
	Breathing is paralyzed immediately - in a fraction of a second. Fibrillation of the heart, as a rule, does not occur; possible temporary cardiac arrest during the current flow. With prolonged current flow (several seconds), severe burns, tissue destruction