Electric energy makes life much easier for all of us. Nowadays a person is surrounded by simply a huge number of devices powered by the electrical network.

However, this source of energy is dangerous for humans, or rather, one of its parameters is dangerous - the current strength.

Voltage and frequency of current, dangerous or not?

Voltage and frequency are much safer than current.

For example, a car ignition coil at the output generates an energy pulse with a voltage of 20-24 thousand V, but due to the very low current strength, such a pulse is not dangerous to humans, the maximum that it causes is an unpleasant sensation.

But if the current strength in the coil pulse was much greater, this pulse would be fatal to a person. That’s why it is said that “current kills.”

Its effect on the human body depends on many parameters, and first of all, it is the strength of the current and its type (constant, variable).

The impact also depends on the time of human contact with the source of electricity.

A person’s susceptibility to the effects, his physical and emotional state also influences.

If one person may practically not feel the effect of a current of a certain strength, then the second may already feel this value, and strongly.

The path of electrical discharge through the body is also important.

The most dangerous route is through the central nervous system, respiratory organs and heart.

The effect of current of different magnitudes on the body

The minimum current value that can be felt by a person is 1 mA. But again this value depends on susceptibility.

When this parameter increases, unpleasant pain sensations appear and the muscles begin to contract involuntarily.

Up to 12-15 mA, the current strength is called tear-off. A person is able to independently break contact with the source, although as the parameter approaches the specified values, it becomes increasingly difficult to break contact.

Over 15 mA, the current is considered unbreakable; a person is not able to break the contact himself; outside help is required.

When the parameter increases to 25 mA, the muscles at the point of contact are completely paralyzed, and this is accompanied by very severe pain, and the person’s breathing becomes more difficult.

A current of up to 50 mA, in addition to very severe pain and muscle paralysis, is accompanied by respiratory paralysis and decreased heart activity, the person loses consciousness.

A current value of up to 80 mA leads to respiratory paralysis within a few seconds of exposure; with longer contact, cardiac fibrillation is possible.

100 mA very quickly leads to fibrillation and then to cardiac paralysis.

A current of 5A instantly leads to respiratory paralysis, the heart stops while a person is in contact with the source, and burns form at the site of contact.

Types of impact

There are several types of effects that electric current can have on the human body.

Thermal.

The first type is thermal effects. With such exposure, burns appear on the skin, it can affect tissues, blood vessels overheat, and the functioning of organs is disrupted along the path of the current.

Chemical.

The second is chemical exposure. It is accompanied by the occurrence of electrolysis of fluids inside a person; blood and lymph are broken down, which leads to a change in their physicochemical composition.

Mechanical.

The third impact is mechanical. When it occurs, human tissue ruptures, and cracks may appear in the bones.

Biological.

The last type of impact is biological. Exposure to current leads to cramps of muscles and organs, disruption of organ activity, up to the complete cessation of their functioning.

Types of Electrical Injuries

Electrical injuries that electric current can cause to the body are divided into external and internal.

There are several external electrical injuries. The most common herbal is burn. Most electrical injuries result in burns.

However, there are also other types of electrical injuries.:

The signs are oval in shape and appear on the skin as pale yellow or gray spots. Since the skin at the point of contact dies upon exposure, the marks are not painful, the area of skin hardens somewhat and fades over time;
Metallization is the transfer of wire metal particles to the skin as a result of an electric arc appearing between the wire and human skin. The area of skin where metallization has occurred is painful, the affected area takes on a metallic tint;
Ophthalmia is the effect of ultraviolet rays of an electric arc on the membrane of the eye, causing it to become inflamed. Accompanied by the appearance over time of severe pain in the eyes and lacrimation. After a while, the unpleasant sensations pass;
Mechanical damage - when exposed, muscle cramps that appear can lead to rupture of tissues, blood vessels, and skin.

Internal damage when struck occurs due to electrical shock.

When current passes through internal organs, their tissues are excited, which is accompanied by dysfunction.

Electric shock is the most dangerous type of injury.

The degree of influence of current on the body

The effect of electric current on the human body has a certain classification, which is divided into 4 degrees.

First degree– exposure of a person to a source of electricity with a low current strength, at which involuntary muscle contraction occurs, but the person is conscious.

Second degree– the source of electricity has an average current strength, is accompanied by muscle contraction, the person loses consciousness, but breathing and pulse are present.

Third degree– contact of a person with a source of energy with a high current strength, due to which paralysis of the respiratory system occurs, and it is absent, and the functioning of the heart is impaired.

Fourth degree– exposure of a person to electricity with a very high current strength, at which breathing and heart function are absent, clinical death occurs.

Safety precautions

To prevent possible electric shock to a person, there are a number of rules prescribed in the safety and labor protection instructions.

Thus, work with electrical devices should be carried out only with tools with protected handles that do not allow current to pass through.

Repairs to electrical appliances should only be carried out after de-energizing them and removing the plug from the socket.

Repairs to electrical networks must be carried out after a power outage. At the same time, corresponding signs are hung on the switches that were used to de-energize.

When working with powerful devices, dielectric mats, shoes, and gloves are additionally used.

And for children there are special electrical safety rules.

Providing assistance in case of defeat

If a person comes under the influence of electric current, a number of specific measures are taken.

The first thing to do is to break the person’s contact with the source. This can be done by de-energizing the network or device with which contact occurred.

Occurs when the human body comes into contact with a voltage source.

By touching a live conductor, a person becomes part of the electrical network through which electric current begins to flow.

As you know, the human body consists of a large amount of salts and liquid, which is a good conductor of electricity, so the effect of electric current on the human body can be lethal.

Types of effects of electric current on the human body

Consequences that will arise as a result the effect of electric current on a person depend on many factors, namely:

Depending on the magnitude and type of current flowing, alternating current is more dangerous than direct current;

The duration of its impact, the longer the time effects of current on a person, the more severe the consequences;

Pathways, the greatest danger is the current flowing through the brain and spinal cord, the area of the heart and respiratory organs (lungs);

From the physical and psychological state of a person. The human body has a certain resistance, this resistance varies depending on the person’s condition.

The minimum amount of current that the human body can feel is 1 mA.

When the current increases to more than 1 mA, a person begins to feel uncomfortable, painful muscle contractions occur, when the current increases to 12-15 mA, convulsive muscle contractions occur, the person is no longer able to control his muscular system and cannot break contact with the current source on his own. This current is called unreleased.

The action of an electric current of more than 25 mA leads to paralysis of the respiratory muscles, as a result of which a person can simply suffocate. With a further increase in current, cardiac fibrillation occurs.

Electric current passing through the human body can have three types of effects on it:

-thermal;
- electrolytic;
- biological.

Thermal action Current implies the appearance of burns of various forms on the body, overheating of blood vessels and disruption of the functionality of internal organs that are affected by the flow of current.

Electrolytic action manifests itself in the breakdown of blood and other organic fluid in the tissues of the body, causing significant changes in its physical and chemical composition.

Biological effect causes disruption of the normal functioning of the muscular system. Involuntary convulsive muscle contractions occur; this effect on the respiratory and circulatory organs, such as the lungs and heart, is dangerous; this can lead to disruption of their normal functioning, including the absolute cessation of their functionality.

The main factors of damage that arise as a result of the action of electric current on a person are:

Electrical injuries- local damage to body tissues as a result of the action of electric current or electric arc. Electrical injuries include injuries such as electrical burns, electrical marks, metallization of the skin, and mechanical damage.

The most common electrical injury is electrical burns, accounting for approximately 60% of all electrical injuries. Electrical burns can be either current or arc.

Electrical signs- appear on the skin of a person who has been exposed to current, in the form of oval-shaped spots of gray or pale yellow color. As a rule, they are painless, harden like a callus, and over time the dead layer of skin comes off on its own.

Metallization of leather- occurs as a result of penetration of small metal particles into the upper layer of the skin, which have melted under the action of an electric arc. The skin at the site of the lesion becomes painful, becomes hard, and takes on a dark metallic tint.

Electroophthalmia– occurs as a result of inflammation of the outer membrane of the eyes under the influence of ultraviolet rays of an electric arc. For protection, you must use safety glasses and masks with colored lenses.

Mechanical damage manifest themselves under the influence of current, involuntary convulsive muscle contractions. This can lead to rupture of skin, blood vessels and nerve tissue.

Of the above damages that occur as a result action of electric current on the human body, the most dangerous are electrical shocks. Electric shock is accompanied by stimulation of living tissues of the body by the current that passes through it. At this moment, involuntary convulsive muscle contractions occur.

The effects of electric current on a person are extremely diverse in nature and type. They depend on many factors.

According to the nature of the impact, they are distinguished: thermal, biological, electrolytic, chemical and mechanical damage.

The thermal effect of the current is manifested by burns of individual parts of the body, blackening and charring of the skin and soft tissues; heating organs located in the path of current, blood vessels and nerve fibers to a high temperature. The heating factor causes functional disorders in the organs and systems of the human body.

The electrolytic effect of current is expressed in the decomposition of various body fluids into ions that violate their properties.

The chemical effect of current is manifested in the occurrence of chemical reactions in the blood, lymph, and nerve fibers with the formation of new substances that are not characteristic of the body.

The biological effect leads to irritation and excitation of living tissues of the body, the occurrence of convulsions, respiratory arrest, and changes in the mode of cardiac activity.

The mechanical effect of the current is expressed in a strong contraction of muscles, up to their rupture, ruptures of the skin, blood vessels, bone fractures, dislocation of joints, and tissue separation.

According to the types of damage, they are distinguished: electrical injuries and electrical

Electrical injuries are local lesions (burns, electrical marks, metallization of the skin, mechanical damage, electroophthalmia).

Electrical burns are divided into contact and arc. Contact ones occur at the point of contact of the skin with the current-carrying part of an electrical installation with a voltage not exceeding 2 kV, arc ones - in places where an electric arc has occurred, which has a high temperature and high energy. The arc can cause extensive body burns, charring, and even complete burning of large areas of the body.

Electrical marks are dense gray or pale yellow areas on the surface of a person's skin that has been exposed to current. As a rule, the skin loses sensitivity at the site of the electric sign.

Metallization of the skin is the introduction into the upper layers of the skin of the smallest particles of metal melted under the action of an electric arc or charged particles of electrolyte from electrolysis baths.

Electroophthalmia is an inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet radiation from an electric arc. Damage to the cornea is possible, which is especially dangerous.

Electrical shocks are common lesions associated with the excitation of tissues by current passing through them (malfunctions in the functioning of the central nervous system, respiratory and circulatory organs, loss of consciousness, speech disorders, convulsions, respiratory failure until it stops, instant death).

According to the degree of impact on a person, three threshold current values are distinguished: palpable, non-releasing and fibrillation.

Sensible is an electrical current that, when passing through the body, causes noticeable irritation. The sensation of alternating electric current flow usually starts at 0.6 mA.

Non-releasing current is a current that, when passing through a person, causes irresistible convulsive contractions of the muscles of the arms, legs or other parts of the body in contact with the current-carrying conductor. An alternating current of industrial frequency, flowing through nerve tissues, affects the biocurrents of the brain, causing the effect of “chaining” to an uninsulated current conductor at the point of contact with it. A person cannot independently tear himself away from the live part.

Fibrillation is a current that, when passing through the body, causes fibrillation of the heart (multi-time uncoordinated contractions of individual muscle fibers of the heart). Fibrillation can lead to cardiac arrest and respiratory paralysis.

The degree of electric shock depends on electrical conductivity or its inverse parameter - the general electrical resistance of the body. They, in turn, are determined:

Individual characteristics of the human body;

Parameters of the electrical circuit (voltage, strength and type of current, frequency of its oscillations) under which the employee fell;

By passing current through the human body;

Conditions for inclusion in the electrical network;

Duration of exposure;

Environmental conditions (temperature, humidity, presence of conductive dust, etc.).

Low electrical resistance of the body contributes to more severe consequences of damage. The electrical resistance of the human body decreases due to unfavorable physiological and psychological conditions (fatigue, illness, alcohol intoxication, hunger, emotional arousal).

The total electrical resistance of the human body is summed up from the resistance of each part of the body located along the path of current flow. Each section has its own resistance. The upper stratum corneum of the skin, which lacks nerve endings and blood vessels, has the greatest electrical resistance. When the skin is wet or damaged, the resistance is about 1000 ohms. With dry skin without damage, it increases many times over. During electrical breakdown of the outer layer of skin, the total resistance of the human body is significantly reduced. The longer the current flow, the faster the skin resistance drops.

The severity of a person's injury is proportional to the strength of the current passing through his body. A current of more than 0.05 A can fatally injure a person with a duration of exposure of 0.1 s.

Alternating current is more dangerous than direct current, but at high voltages (more than 500 V), direct current becomes more dangerous. The most dangerous frequency range of alternating current is from 20 to 100 Hz. The bulk of industrial equipment operates at a frequency of 50 Hz, which is within this dangerous range. High frequency currents are less dangerous. High frequency currents can only cause superficial burns, as they spread only over the surface of the body.

The degree of damage to the body largely determines the path along which the electric current passes through the human body. The most common options in practice are 1, 2, 5, 6, 7, shown in Fig. 2.1.

Rice. 2.1. Options for the passage of electric current through the human body: 1 - “hand-to-hand”; 2 - “arm and legs”; 5 — “leg-to-leg”; 6 - “head-legs”; 7 - “head-hand”

A person touches live wires or live parts of equipment with both hands. In this case, the current flows from one hand to the other through the lungs and heart. This path is usually called “hand - hand”;

A person stands with both feet on the ground and touches the current source with one hand. The path of current flow in this case is called “arm - legs”. The current passes through the lungs and possibly the heart;

A person stands with both feet on the ground in the zone where current flows to the ground from faulty electrical equipment, which in this case acts as a ground electrode. The earth within a radius of up to 20 m receives a voltage potential that decreases with distance from the ground electrode. Each of a person’s legs receives a different voltage potential, determined by the distance from the faulty electrical equipment. As a result, an electrical circuit “leg-leg” arises, the voltage in which is called step-by-step;

Touching live parts with your head can create a circuit where the current path is “head - hands” or “head - feet”.

The most dangerous options are those in which the vital systems of the body - the brain, heart, lungs - fall into the affected area. These are chains: “head - hand”, “head - feet”, “hands - feet”, “hand - hand”.

Example. Alternating current with a frequency of 50 Hz and a voltage of 220 V, which is standard for domestic electrical networks, when passing along the hand-to-foot path, depending on the current strength, can have different effects. So, if the current strength is 0.6-1.5 mA, it is already noticeable. It is accompanied by mild itching and slight trembling of the fingers. At a current strength of 2.0-2.5 mA, pain and severe trembling of the fingers appear. At a current strength of 5.0-7.0 mA, cramps of the hands occur. A current of 20.0-25.0 mA is already a non-releasing current. The person cannot independently tear his hands away from the conductor; there is severe pain and cramps, and difficulty breathing. When the current is 50.0-80.0 mA, respiratory paralysis occurs (if the current flows for a long time, cardiac fibrillation may occur). At 90.0-100.0 mA, fibrillation occurs. After 2-3 seconds, respiratory paralysis occurs (Table 2.1).

Table 2.1. The nature of the impact on a person when electric current flows through the body (parts of the body)

The flow of direct current through the human body with a voltage of less than 500 V causes pain at the point of contact with the conductor, in the joints of the limbs, painful shock, and burns. However, it can also lead to respiratory or cardiac arrest. At voltages of 500 V and above, there are practically no differences in the effects of direct and alternating currents.

There is a nonlinear relationship between the current flowing through the human body and the voltage applied to it. As the voltage increases, the current increases faster than the voltage.

The degree of danger of electric shock depends on the conditions under which a person is connected to the electrical network. In production, three-phase AC electrical networks (with an isolated neutral or with a grounded neutral) and single-phase electrical networks are used. All of them are dangerous, but each has a different degree of danger.

For three-phase AC networks with any neutral mode, the most dangerous is two-phase contact (simultaneously to two wires of a working network). A person closes two phase wires through his body and comes under the full line voltage of the network. In this case, the current passes along the most dangerous “hand-to-hand” path. The current strength is maximum, since only a very low (about 1000 Ohm) resistance of the human body is connected to the network. Two-phase contact with active parts of the installation even at a voltage of 100 V can be fatal.

If you touch the wire of an installation in emergency mode (break of the second wire and short circuit of a phase to ground), due to the redistribution of voltages between phases, the risk of serious electric shock to a person is somewhat reduced.

Three-phase electrical networks with a grounded neutral are somewhat less dangerous than networks with an isolated neutral. Such networks have very low resistance between the neutral and ground, so grounding the neutral serves safety purposes.

The least dangerous thing is always to touch one of the wires of a working network.

When a broken wire falls onto the ground or when the insulation is damaged and a phase breakdown occurs through the equipment body to the ground, as well as at the locations of the ground electrode, the fault current spreads into the ground. It obeys the hyperbolic law (Fig. 2.2).

Rice. 2.2. Diagram of the spread of fault current in the ground: 1 - place where a broken wire falls to the ground; 2 - curve (hyperbola) of the distribution of potentials on the surface of the earth during current spreading; U3 - voltage at the fault point

Since the ground is a significant resistance for the spread of current, all points located on the same radial straight line, but at different distances from the point of closure of the conductor to the ground, will have different potentials. It is maximum at the ground electrode, decreases with distance from it and is equal to zero beyond the boundary of the spreading zone. At a distance of 1 m from the ground electrode, the voltage drop in dry soil is already 68%, at a distance of 10 m - 92%. Finding a person in the current flow zone close to the ground electrode can be dangerous.

It is necessary to leave the danger zone in very small steps along the radius. According to the “Safety Instructions for the operation of traction substations, power supply points and sectioning of electrified railways” No. TsE-402, approved by the Ministry of Railways of Russia on October 17, 1996, move in the zone of spreading ground fault current without protective equipment (dielectric galoshes, boat) follows by moving your feet on the ground and without lifting them from one another. As the step length increases, the difference in the potentials under which each leg is located increases. The voltage formed due to the potential difference in the current spreading zone between two points on the earth's surface, which are spaced from each other in the radial direction at a step distance (0.8 m), is called step voltage. The current path with a leg-to-leg step voltage does not touch vital organs. However, with significant stress, leg cramps occur and the person falls. In this case, the electrical circuit is closed through the entire body of the fallen person.

In single-phase DC networks, the most dangerous is also a person touching two wires at the same time, since in this case the current flowing through the human body is determined only by the resistance of his body.

The duration of current exposure is often a factor on which the outcome of the injury depends. The longer the electric current affects the body, the more severe the consequences. After 30 s, the resistance of the human body to the flow of current drops by approximately 25%, and after 90 s - by 70%.

Action El. current on the human body, types of exposure, types of damage

Electrical safety b 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 and static electricity in order to reduce electrical injuries to an acceptable level of risk and below.

A distinctive feature of electric current from other industrial hazards and hazards (except radiation) is that a person is not able to detect electrical voltage remotely with his senses.

In most countries of the world, statistics of accidents due to electrical shock show that the total number of injuries caused by electric current with loss of ability to work is small and amounts to approximately 0.5-1% (in the energy sector - 3-3.5%) of the total number of accidents in production. However, fatalities in such cases in production amount to 30-40%, and in the energy sector up to 60%. According to statistics, 75-80% of fatal electric shocks occur in installations up to 1000 V.

Electric current flows through the human body if there is a potential difference between two points. The voltage between two points in a current circuit that are simultaneously touched by a person is called touch tension

The effect of electric current on the human body

Passing through the body, electric current causes thermal, electrolytic and biological effects.

Thermal action is expressed in burns of individual parts of the body, heating of blood vessels and nerve fibers.

Electrolytic action is expressed in the decomposition of blood and other organic liquids, causing significant disturbances in their physical and chemical compositions.

Biological effect manifests itself in irritation and excitation of living tissues of the body, which can be accompanied by involuntary convulsive contractions of muscles, including the muscles of the heart and lungs. As a result, various disorders in the body may occur, including disruption and even complete cessation of the respiratory and circulatory system.

The irritating effect of current on tissue can be direct, when the current passes directly through these tissues, and reflexive, that is, through the central nervous system, when the path of the current lies outside these organs.

All the variety of effects of electric current leads to two types of damage: electrical injuries and electric shocks.

Electrical injuries- these are clearly defined local damage to body tissues caused by exposure to electric current or electric arc (electrical burns, electrical marks, metallization of the skin, mechanical damage).

Electric shock- this is the excitation of living tissues of the body by an electric current passing through it, accompanied by involuntary convulsive muscle contractions.

Distinguish four degrees of electric shocks:

I degree - convulsive muscle contraction without loss of consciousness;

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

III degree - loss of consciousness and disturbance of cardiac activity or breathing (or both);

IV degree - clinical death, that is, lack of breathing and blood circulation.

Clinical ("imaginary") death- This is a transitional process from life to death, occurring from the moment the activity of the heart and lungs ceases. 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 (4-5 minutes, and in the case of the death of a healthy person from accidental causes - 7-8 minutes). Biological (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. Biological death occurs after a period of clinical death.

Thus, causes of death from electric shock There may be cessation of heart function, cessation of breathing, and electric shock.

Cardiac arrest or fibrillation, that is, chaotic fast and multi-temporal contractions of the fibers (fibrils) of the heart muscle, in which the heart stops working as a pump, resulting in blood circulation in the body stopping, can occur due to the direct or reflex action of an electric current.

Cessation of breathing as the root 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 (as a result - asphyxia or suffocation due to lack of oxygen and excess carbon dioxide in the body).

Types of electrical injuries:

- electrical burns –

Electrometallization of leather

Electrical signs

Electric shocks

Electroophthalmia

Mechanical damage

Electrical burn and arise from the thermal action of electric current. The most dangerous are burns that occur as a result of exposure to an electric arc, since its temperature can exceed 3000°C.

Electrometallization of leather- penetration of tiny metal particles into the skin under the influence of electric current. As a result, the skin becomes electrically conductive, i.e. its resistance drops sharply.

Electrical signs-- spots of gray or pale yellow color that appear in close contact with a live part (from which electric current flows in operating condition). The nature of electrical signs has not yet been sufficiently studied.

Electroophthalmia- damage to the outer membranes of the eyes due to exposure to ultraviolet radiation from an electric arc.

Electric shocks are a general lesion of the human body, characterized by convulsive contractions muscles, disorders of the human nervous and cardiovascular systems. Electrical shocks often lead to death.

Mechanical damage(tissue ruptures, fractures) occur due to convulsive muscle contractions, as well as as a result of falls when exposed to electric current.

The nature of electric shock and its consequences depend on the value and type of current, the path of its passage, the duration of exposure, the individual physiological characteristics of a person and his condition at the time of the injury.

Electric shock- this is a severe neuro-reflex reaction of the body in response to strong electrical stimulation, accompanied by dangerous disorders of blood circulation, breathing, metabolism, etc. This condition can last from several minutes to days.

Basically, the value and type of current determine the nature of the lesion. In electrical installations up to 500 V, alternating current of industrial frequency (50 Hz) is more dangerous to humans than direct current. This is due to complex biological processes occurring in the cells of the human body. As the frequency of the current increases, the risk of injury decreases. At frequencies of the order of several hundred kilohertz, electrical shocks are not observed. Depending on the value of their effect on the human body, currents are divided into tangible, not letting go And fibrillation.Sensible currents- currents that cause noticeable irritation when passing through the body. A person begins to feel the effects of alternating current (50 Hz) at values from 0.5 to 1.5 mA and direct current - from 5 to 7 mA. Within these values, slight trembling of the fingers, tingling, and heating of the skin (with constant current) are observed. Such currents are called threshold perceptible currents.

Non-releasing currents cause convulsive contraction of the arm muscles. The smallest current value at which a person cannot independently tear his hands away from live parts is called threshold non-releasing current. For alternating current this value ranges from 10 to 15 mA, for direct current - 50 to 80 mA. With a further increase in current, damage to the cardiovascular system begins. Breathing becomes difficult and then stops, and the work of the heart changes.

fibrillation currents cause cardiac fibrillation - fluttering or arrhythmic contraction and relaxation of the heart muscle. As a result of fibrillation, blood from the heart does not flow to vital organs and, first of all, the blood supply to the brain is disrupted. The human brain, deprived of blood supply, lives for 5 - 8 minutes and then dies, so in this case it is very important to quickly and timely provide first aid to the victim. Fibrillation current values range from 80 to 5000 mA

Factors influencing the outcome of the lesion El. electric shock

The outcome of the effect of electric current on the human body depends on a number of factors, the main of which are: the electrical resistance of the human body; the magnitude of the electric current; the duration of its effect on the body; the amount of stress affecting the body; type and frequency of current; the path of current flow in the body; psychophysiological state of the body, its individual properties; state and characteristics of the environment (air temperature, humidity, gas and dust levels in the air), etc.

Current strengthI. Currents:

0,6 – 1,5 mA: there is a sensation (of change), not felt (constant)

5 - 7mA: convulsions in the hands (of change), a feeling arises (constant)

20 -25mA: threshold, not letting go - hands are paralyzed, impossible to tear away from the equipment, slowing of breathing (changes), slight muscle contraction (constant)

50 - 80mA: fibrillation - arrhythmic contraction or relaxation of the heart muscles

	At AC 50 Hz	At constant current
	The appearance of a sensation, slight trembling of the fingers	Not felt
	Cramps in the hands	Sensation occurs, skin heating Increases heating
	It’s difficult, but you can still tear your hands away from the electrodes; severe pain in the hands and forearms	Increased heating
	Hands become paralyzed, it is impossible to tear them away from the electrodes, breathing is difficult	Minor muscle contraction
	Stopping breathing. Onset of cardiac fibrillation	Strong heat; contraction of arm muscles;
	difficulty breathing	Stopping breathing and cardiac activity (with exposure lasting more than 3 s)

Stopping breathing Duration of exposure to current on the human body

If the current does not go away, but does not yet disrupt breathing and heart function, a quick shutdown saves the victim, who would not be able to free himself. With prolonged exposure to current, the resistance of the human body drops and the current increases to a value that can cause respiratory arrest or even cardiac fibrillation.

Stopping breathing does not occur instantly, but after a few seconds, and the greater the current through a person, the shorter this time. Timely disconnection of the victim helps prevent the cessation of the respiratory muscles.

Thus, the shorter the duration of the current on a person, the less likely it is that the time during which the current passes through the heart will coincide with phase T.

Path of current in the human body. The most dangerous current is the passage of current through the respiratory muscles and heart. Thus, it was noted that along the path “arm-arm” 3.3% of the total current passes through the heart, “left arm-legs” - 3.7%, “right arm-legs” - 6.7%, “leg-leg " - 0.4%, "head - legs" - 6.8%, "head - arms" - 7%. According to statistics, loss of ability to work for three days or more was observed with the current path "arm - arm" in 83% of cases, "left arm - legs" - in 80%, "right arm - legs" - 87%, "leg - leg" - in 15% of cases.

Thus, the path of the current influences the outcome of the lesion; The current in the human body does not necessarily pass along the shortest path, which is explained by the large difference in the resistivity of various tissues (bone, muscle, fat, etc.).

The smallest current passes through the heart when the current path is along the lower leg-to-leg loop. However, one should not draw conclusions from this about the low danger of the lower loop (the effect of step voltage). Usually, if the current is strong enough, it causes leg cramps and the person falls, after which the current can already pass through the chest, that is, through the respiratory muscles and heart. Most dangerous- this is the path passing through the brain and spinal cord, heart, lungs

Type and frequency of current. It has been established that alternating current with a frequency of 50-60 Hz is more dangerous than direct current. since the same effects are caused by larger values of direct current than alternating current. However, even a small direct current (below the threshold of sensation) with a rapid break in the circuit gives very sharp shocks, sometimes causing cramps in the arm muscles.

Many researchers argue that alternating current with a frequency of 50-60 Hz is the most dangerous. Current hazard decreases with increasing frequency, but current with a frequency of 500 Hz is no less dangerous than 50 Hz.

Human body resistance is not constant and depends on many factors - the condition of the skin, the size and density of the contact, the applied voltage and the time of exposure to the current.

Usually, when analyzing the dangers of electrical networks and when making calculations, it is customary to consider the resistance of the human body to be active and equal to 1 kOhm.

The nature of the damage also depends on the duration of the current. With prolonged exposure to current, the heating of the skin increases, the skin becomes moisturized due to sweating, its resistance drops and the current passing through the human body increases sharply.

The nature of the lesion is also determined by the individual physiological characteristics of the person. If a person is physically healthy, then electrical shock will be less severe. In case of diseases of the cardiovascular system, skin, nervous system, or alcohol intoxication, electrical injury can be extremely serious even with small applied currents.

The psychophysiological preparedness of the worker for the impact has an important influence on the outcome of the injury. If a person is attentive, focused when performing work, and prepared for the fact that he may be exposed to electrical current, then the injury may be less severe.

ENVIRONMENTAL PARAMETERS: temperature, humidity, dust

Physiological characteristics of the body at the time of injury

Applied voltage dependence is directly proportional

Phenomenon when current flows into the ground

The leg-to-leg path is least dangerous. Most often, such a path occurs when a person comes under the influence of the so-called step tension, i.e., between points on the earth’s surface located at a distance of a step from each other.

If there is a short circuit to the ground of any circuit - an accidental electrical connection of the current-carrying part directly to the ground or through metal structures, then an electric current will flow along the ground, called ground fault current. The earth potential, as it moves away from the fault point, will change from maximum to zero value,

since the soil resists the ground fault current.

Fig.1 Turning on a person to step voltage

If a person enters the current spreading zone, then there will be a potential difference between his feet, which will cause current to flow along the leg-to-leg path. The result of the current may be a contraction of the leg muscles, and the person may fall. The fall will cause the formation of a new, more dangerous current circuit through the heart and lungs.

In Fig. Figure 3.1 shows the formation of step voltage and shows the potential distribution curve on the earth's surface. At a distance of 20 m from the fault point, the potential can be considered zero. Rice. 3.1. Turning on a person's step voltage

The value of the current passing through the human body depends on the applied voltage and the resistance of the body. The higher the voltage, the more current passes through a person

(I 2 - the path of passage is more dangerous and the current strength is higher)

Touch and step stresses

Step voltage is the voltage on the surface of the earth between points located at a step distance from each other.

Touch voltage is the potential difference between two electrical points. the chains of which are simultaneously touched by a person.

To reduce the difference φ 2 -φ 1, you need to leave the spreading zone in small steps

Classification of premises according to the degree of danger of electric shock

Electrical installations are installations in which electrical energy is produced, converted, distributed and consumed. Electrical installations include generators and electric motors, transformers and rectifiers, wire, radio and television communication equipment, etc.

Safety of work in electrical installations depends on the electrical circuit and parameters of the electrical installation, rated voltage, environment and operating conditions. From a safety point of view, all electrical installations, according to the PUE, are divided into installations up to 1000 V and installations above 1000 V. Since installations above 1000 V are more dangerous, more stringent requirements are imposed on protective measures.

Electrical installations can be located indoors or outdoors. Environmental conditions have a significant impact on the state of insulation of an electrical installation, on

resistance of the human body, and therefore safe? service personnel. Working conditions according to the degree of electrical safety are divided into three categories: with increased danger of electric shock to people; especially dangerous; without increased danger.

Terms with increased danger characterized by the presence of one of the following features: - conductive bases (reinforced concrete, earthen, metal, brick);

Conductive dust that worsens the cooling conditions of insulation, but does not cause a fire hazard;

Dampness (relative humidity greater than 75%);

Temperature exceeding +35°C for a long time;

The possibility of simultaneous human touch to grounded metal structures, on the one hand, and to metal housings of electrical equipment, on the other.

To reduce the risk of electric shock under these conditions, low voltage (42 V or less) is recommended.

Particularly hazardous conditions characterized by the presence of one of the following characteristics:

special dampness (relative humidity close to 100%);

chemically active environment that destroys insulation and live parts of electrical equipment;

at least two signs of increased danger.

In conditions without increased danger, the above signs are absent

The effect of electric current on the human body

The electric power industry (power plants, electrical networks) is saturated with electrical installations, which are a factor of increased danger due to the possibility of traumatic effects of electric current on a person with all the ensuing consequences. The effect of electric current on the human body is diverse.

Electric current passing through the human body has thermal, chemical and biological effects.

Thermal (thermal) effect manifests itself in the form of burns of the skin, overheating of various organs, as well as ruptures of blood vessels and nerve fibers resulting from overheating.

Chemical (electrolytic) action leads to electrolysis of blood and other solutions contained in the human body, which leads to a change in their physico-chemical compositions, and therefore to disruption of the normal functioning of the body.

Biological effect manifests itself in dangerous stimulation of living cells and tissues of the body, as a result of which they can die.

The degree of dangerous and harmful effects of electric current on a person depends on:

parameters of the electric current flowing through the human body (voltage, frequency, type of current applied to the body),
current paths through the human body (arm-arm, arm-leg, leg-leg, neck-legs, etc.),
duration of exposure to current through the human body,
environmental conditions (humidity and temperature),
state of the human body (thickness and moisture content of the skin, health status and age).

The dangerous and harmful effects of electric current on people manifest themselves in the form of electric shocks and electrical injuries.

Electric shock This is the effect of electric current on the human body, as a result of which the muscles of the body (for example, arms, legs, etc.) begin to contract convulsively.

Depending on the magnitude of the electric current and the time of its exposure, a person may be conscious or unconscious, but the normal functioning of the heart and breathing is ensured. In more severe cases, loss of consciousness is accompanied by disruption of the human cardiovascular system and even leads to death. As a result of an electric shock, paralysis of the most important organs of the human body (heart, lungs, brain, etc.) is possible.

Electrical injury This is the effect of electric current on the human body, which damages human tissues and internal organs (skin, muscles, bones, etc.).

Of particular danger are electrical injuries in the form of burns at the point of contact of the human body with live parts of electrical installations or burns from an electric arc, including metallization of the skin (metalization of the skin is the penetration of the smallest particles of metal into the upper layers of the skin when the arc burns). As well as various mechanical damage (bruises, wounds, fractures) arising from sudden involuntary movements of a person when exposed to electric current. (Secondary consequences caused by a fall from a height or involuntary blows are possible).

As a result of severe forms of electric shock and electrical trauma, a person may find himself in a state of clinical death - his breathing and blood circulation stop. In the absence of medical care, clinical death can turn into biological death. However, in some cases, with proper medical care (artificial respiration and cardiac massage), the victim can be revived.

The immediate causes of death of a person struck by electric current are cessation of heart function, respiratory arrest and so-called electric shock.

Stopping the heart possibly as a result of the direct action of electric current on the heart muscle or, reflexively, due to paralysis of the nervous system. In this case, complete cardiac arrest or so-called fibrillation may occur, in which the fibers of the heart muscle (fibrils) enter a state of rapid chaotic contractions.

Stopping breathing due to paralysis of the chest muscles can be the result of either the direct passage of an electric current through the chest area or reflexively, due to paralysis of the nervous system.

The nervous reaction of the human body to stimulation by electric current, which manifests itself in disruption of normal breathing, blood circulation and metabolism, is called electric shock .

With prolonged shock, death can occur. If the victim is provided with medical assistance in a timely manner, the state of shock can be relieved without consequences for the person.

The main factor determining the outcome of an electric shock to a person is the value of the electric current flowing through the human body. The amount of current in the human body is determined by the applied voltage and the electrical resistance of the person. A person's resistance depends on a number of factors. It must be borne in mind that different tissues and organs of the human body have different resistivities. The resistance of dry skin and bone tissue has the greatest value, while the resistance of blood and cerebrospinal fluid is small.

The stratum corneum of human skin does not have blood vessels and has a very high resistivity - about 10 8 Ohm×cm. The inner layers of the skin, saturated with blood vessels, glands and nerve endings, have insignificant resistivity.

Conventionally, we can consider the human body as part of an electrical circuit consisting of 3 sections connected in series: skin - internal organs - skin.

The electrical circuit diagram of a human replacement is shown in Fig. 1.1.

Fig. 1.1 Schematic electrical circuit diagram of human replacement, where: G k- skin resistance; From to- capacitance between the electrode and the inside of the body; G vn- resistance of internal organs

The value of capacitance (c k) is generally insignificant and therefore it is often neglected, taking into account only the value of resistance 2r to +r int.

The resistance of the human body (R h) is a variable value that depends on the condition of the person’s skin (thickness of the horny skin, humidity) and the environment (humidity and temperature).

The surface skin, consisting of a layer of keratinized cells, has a high resistance - in dry skin it can have values of up to 500 kOhm. Damage to the stratum corneum of the skin (cuts, scratches, abrasions) reduces the resistance of the human body to 500-700 Ohms, which proportionally increases the risk of electric shock to a person. Much less resistance to electric current is provided by muscle, fat, bone tissue, blood, and nerve fibers. In general, the resistance of human internal organs is 400-600 Ohms.

In electrical calculations, the calculated value of the resistance of the human body is taken to be 1000 Ohms.

Current and voltage magnitude

The main factor influencing the outcome of an electric shock to a person is the magnitude of the current, which, according to Ohm's law, depends on the magnitude of the applied voltage and the resistance of the human body.

This dependence is not linear, since at voltages of about 100 V and higher, a breakdown of the upper stratum corneum of the skin occurs, as a result of which the electrical resistance of a person sharply decreases (becomes equal to r vn), and the current increases. The voltage applied to the human body also affects the outcome of the injury, but only insofar as it determines the value of the current passing through the person.

Type and frequency of electric current

The impact on humans of direct and alternating current is different - alternating current of industrial frequency is more dangerous than direct current of the same value. There are several times fewer cases of injury in electrical installations with direct current than in similar installations with alternating current; at higher voltages (more than 300 V), direct current is more dangerous than alternating current (due to intense electrolysis).