Questions and answers on passing the exam in electrical safety of the 2nd group

To whom does it apply I I qualifying group?

Group II applies to electrical personnel.

Who approves the list of professions requiring the assignment of production personnel to II qualifying group?

The list of professions, jobs that require the assignment of production personnel to group II is determined by the head of the organization.

How the assignment is made II qualifying group?

Group II assignment is made by conducting a knowledge test, which is carried out in the form of an examination and (if necessary) testing the acquired skills in safe ways of working or first aid in case of electric shock.

Who has the right to assign II qualifying group?

The assignment of group II is carried out by an attestation commission appointed by the head of the enterprise.

Requirements for personnel II qualifying group.

Requirements for personnel with II electrical safety group:

1. Basic technical knowledge of the electrical installation and its equipment.

2. A clear understanding of the danger electric current, danger of approaching live parts.

3. Knowledge of basic safety precautions when working on electrical installations.

4. Practical skills in providing first aid to victims.

Independent work in electrical installations for personnel with electrical safety group II is prohibited. Work is possible only under the supervision of an employee with an electrical safety group of at least III.

Representation of the danger of electric current

1. What is the main danger of electric shock?

The operation of electrical installations, electrical receivers, portable electric lamps and power tools belongs to the category of work performed in conditions of increased danger, and in terms of safety it differs significantly from the operation of any other equipment.

Usually the threat of an accident is accompanied by some signs to which the human senses can respond. A type of moving vehicle, a falling object, the smell of gas, rotating parts of the car warn a person of danger and enable him to take the necessary precautions.

A person cannot detect an electric current, for this he does not have special sense organs. The insidious feature of electrical energy is that it is invisible, odorless and colorless.

2. How does a person get included in the current flow circuit?

An electric current strikes suddenly when a person is included in the current flow circuit. A dangerous situation arises when, on the one hand, it touches a bare wire, wiring with broken insulation, or a metal case of an electrical appliance with faulty insulation, or a metal object that is accidentally energized, and on the other hand, earth, grounded objects, pipes, etc. (Fig. 1, a and b).

A dangerous situation is detected too late, when it is almost impossible to prevent electric shock.

Another feature of the electric current is that it damages tissues not only at the site of its application, but also along the entire path through the human body.

Electric shock can also occur through an arc contact, when approaching an unacceptably close, dangerous distance to the wire (or bus) of an existing electrical installation, overhead power line (Fig. 1 in). The danger of being hit at a distance increases significantly in wet weather, when the conductivity of the air increases.

An electrical injury can occur when it comes under step voltage that occurs when a wire of an operating overhead line of 0.38 kV and above breaks and falls to the ground (Fig. 2). In this case, the current path is not interrupted. The earth, being a conductor of electric current, becomes, as it were, a continuation of the wire. Electric current flows through the earth. Any point on the earth's surface, located in the zone of current spreading, at the time of its spreading, receives a certain electric potential, which decreases as it moves away from the point of contact of the wire with the ground. An electric shock occurs when a person's feet touch two points on the ground that have different electrical potentials. Step voltage is the difference in potentials located at a step distance. The wider the step, the greater the potential difference, the more likely the defeat. A dangerous zone with a radius of 5-8 meters is formed around a broken wire lying on the ground. Upon entering this zone, a person is in mortal danger if he does not even touch the wire.

Factors on which the effect of electric current on a person depends

The human body is capable of conducting electricity. The effect of electric current on a person depends on a number of factors. They can be divided into three groups:

determined by the electrical parameters of electrical installations (type and frequency of current, voltage, current value and duration of its impact);

depending on individual physiological and psychological features a person, the electrical resistance of his body, the path of the current;

characterizing the environment.

The impact of electric current depends primarily on the value of the current and the time it takes to pass through the human body and can cause discomfort, burns, fainting, convulsions, cessation of breathing and even death.

At the same time, it should be borne in mind that electrical injuries, even with an initial visible successful outcome, can also have long-term consequences. Cases of development of diabetes, diseases of the thyroid gland, genital organs, disorders nervous system and a number of other serious diseases.

Permissible it is assumed that the current is 0.5 mA. A current of 10-16 mA is called relentless(a person cannot independently break away from the electrodes, open the current circuit into which he has fallen). A current of 50 mA affects the respiratory and cardiovascular systems. A current of 100 mA leads to cardiac arrest and disrupts blood circulation, such a current is considered fatal.

It is necessary to keep in mind such a subjective factor as psychological condition person. Fatigue, frustration, drunkenness strongly affect the outcome of the lesion. Under equal conditions for the occurrence of electrical injury, such a person is at greater risk than a normal healthy person.

Electric current is especially dangerous for children and people suffering from chronic diseases, as they are more sensitive to electric current due to their physical data.

The most common electrical injury factors environment(air temperature and humidity, the nature of the premises, the presence of conductive floors, chemically active vapors and gases, etc.). Indeed, elevated temperature and humidity create unfavorable conditions when using electricity: a person's skin is moistened, and the overall resistance of his body is reduced.

The degree of danger of electric shock largely depends on the nature of the premises where the person is located. With regard to electric shock, the premises are divided into three groups:

1. Premises without increased danger, in which there are no conditions that create an increased or special danger.

2. Premises with increased danger, characterized by the presence in them of one of the following conditions:

the presence of dampness (relative humidity exceeds 75% for a long time) or conductive dust;

conductive floors (metal, earthen, reinforced concrete, brick, etc.);

high temperature (35 0 C and above);

the possibility of simultaneous touching of a person to the metal structures of buildings and structures, devices that are connected to the ground, on the one hand, and to the metal cases of electrical installations, on the other.

The presence of one of the listed features is sufficient to classify the production facility in terms of the degree of danger of electric shock to the considered group.

3. Particularly dangerous premises, characterized by the presence of one of the following conditions that create a hazard:

special dampness (relative air humidity is close to 100%: the ceiling, walls, floor and objects in the room are covered with moisture);

chemically active or organic environment (permanently or temporarily formed vapors and deposits that destroy the insulation and current-carrying parts);

the simultaneous presence of two or more conditions of increased danger (metal garages, greenhouses, mines, tanks, etc.).

The presence of one of the listed signs is sufficient for the industrial premises to be classified as especially dangerous according to the degree of danger of electric shock.

With regard to the danger of electric shock to people, the territories where outdoor electrical installations are located are equated to especially dangerous premises.

Electric current is a very dangerous and insidious striking "enemy": a person without instruments is not able to detect its presence in advance, the defeat occurs suddenly. Moreover, its negative impact may not appear immediately: a person may die several days after an electric shock.

Electrical safety measures in the workplace.

Before starting work, you must:

make sure that the electrical equipment being serviced is connected to the mains;

check the presence of protective earth.

During work it is forbidden:

independently engage in the repair of electrical installations;

switch cable connectors of electrical installations when the power supply is on;

allow moisture to get on the surface of electrical installations (it is forbidden to put flowers, vessels with water, glasses with tea, etc. on the equipment).

In an emergency, the employee must:

in all cases of detection of a break in power wires, grounding faults and other damage to electrical installations (broken plug, socket, the insulation of the wires is broken), the appearance of a burning smell immediately turn off the power and report the emergency to the manager and the engineer on duty;

upon detection of a person under voltage, immediately release him from the action of the current by turning off the power supply and, before the arrival of a doctor, provide first aid to the victim;

in the event of a fire in the equipment, turn off the power and take measures to extinguish the fire using a carbon dioxide or powder fire extinguisher, call the fire brigade and report the incident to the manager.

Electricity is a powerful and dangerous element. She faithfully serves a person, however, showing carelessness, or as a result of an accident, you can fall under her blow. Electric shocks occur due to contact with bare wires, knife switches, lampholders and other household and industrial appliances under voltage, non-compliance with safety precautions. Having received an electric shock, a person receives an electrical injury, as a result of which he may remain disabled or even die.

What threatens electric shock

When hit under electrical voltage the victim always gets a shock, but its consequences can be different: from cramps of the fingers of the extremities and their trembling, from unpleasant sensations of heating and burning to respiratory arrest and fibrillation of the heart (unsystematic contraction) and its complete stop. In the latter case, the blood stops moving through the vessels, causing the person to die. In addition, electric current is dangerous for humans, because at certain values ​​of its strength, the effect of sticking to bare wires is created due to excessive stimulation of nerve fibers by electricity. One of the causes of death from electric shock can be mechanical injury as a result of involuntary muscle contraction. Loss of vision may occur due to the effect on the retina of the resulting electric arc.

The skin on the face, on the neck and on the palms on the back side suffer the most from the effects of electric current.

Note! Certain (acupuncture) points on the ears and neck of a person are extremely susceptible to electricity - if they get into them, even a weak current can kill the victim.

Passage through the human body electric charge leaves peculiar marks on it - the so-called. "Electrical marks", which are dead skin with a yellow coating, similar to calluses.

An electric shock burn causes reddening of the skin at the point of contact with its source, blisters with physiological fluid inside are inflated, parts of the body are charred and blackened, sometimes pieces of metal or fabric from clothing are literally “fused” into them. Such burn injuries are treated worse than simple thermal burns, they do not always appear immediately - the consequences can become visible after hours, days or even months (therefore, all victims are under the supervision of doctors for a long time).

Most dangerous current- this is caught in the areas of the back, hands, temporal and occipital parts of the head.

The extent of harm to health from electric shock depends on the direction of current movement inside the human body. As a rule, there are several "routes" of the passage of the charge. The deadly current path for a person is the path from one hand holding a bare wire to the other, because it goes through the lungs, bronchi and heart muscle and causes them to fibrillate. If the victim holds on to a source containing direct current with one hand, and stands on the ground with his feet, the route is called "hand-to-foot", in which case the electricity disrupts the work of almost all internal organs and, of course, heart muscle. The “road” of electricity through the head to the arms or legs is also deadly: if the victim touched the live elements with his head. Sometimes people experience an electrical injury from the so-called. "step voltage" when they are on the ground, receiving electrical direct current without grounding, it passes through the body only through the legs, the heart does not suffer.

What values ​​of current are deadly

Three main factors influence the depth and extent of electric shock:

• current frequency - variable in magnitude and direction or constant;
• current strength;
• the direction of the current as it passes through the human body.

According to the degree of influence on human health, the current is divided into:

• tangible - it gives a person only skin irritation, a safe value is a current strength of up to 0.6 milliamps;
• non-letting - alternating current, which, due to periodic impulses, causes a person to stick to a current source, this happens at a current strength of 0.025 amperes;
• fibrillation - causes fibrillation of internal organs, primarily the heart, which can lead to its stop, the strength of such a current exceeds 0.1 Ampere.

The body of any person resists electric current (described by Ohm's law), its value depends on the general state of health of the victim at the time of the electrical injury, the degree of moisture, mental state and even the quality of the shoes. Knowing the magnitude of the electrical resistance, the values ​​of the voltage are displayed, which becomes dangerous for humans.

According to the canons of electrical safety engineering, the following voltage values ​​​​are considered dangerous to human life and health:

• 65 volts - for residential premises and public buildings with heating and internal humidity of not more than 60 percent;
• 36 volts - for rooms with increased level humidity up to 75 percent (for example, basements, kitchens in canteens and restaurants, metro station lobbies);
• 12 volts - for very humid (up to 100 percent) spaces (pools, baths, laundries, rooms with boilers).

Additional Information. As for the frequency of the current, the danger to life is its value in the range of 50-60 hertz.

If the current strength exceeds 50 milliamps, great harm is done to health, and at values ​​\u200b\u200bmore than 100 milliamps, exposure to electricity for even a few seconds can kill a person.

Which current is more dangerous: AC or DC

Everyone knows that the current is variable and constant, but not everyone understands which one is more harmful to life and health. Experts answer that the most dangerous is the variable species.

Why is alternating current more dangerous than direct current? The reason is that direct current must be three times more powerful than alternating current for the mortal danger of a person, since alternating current affects nerve endings and muscle tissue (primarily cardiac) much stronger and faster. The power of direct current in many cases (with a power of up to 50 milliamps) is covered by the electrical resistance of the human body, while for alternating current this limit is only a dozen milliamps. However, when electricity reaches a voltage of 500 volts, the harm from both types of current is the same, and when it is exceeded, direct current becomes more dangerous.

Our body is a conductor of electric current, which, passing through it, has a detrimental effect on human health and can lead to death. The danger is not only the strength, type and power of the current, but also the duration of exposure and the route of passage through the body. Current resistance depends on many conditions, so in different countries there are various norms, which determine the safe voltage of the electric current.

Video

Why is electric current dangerous and what effect does it have on the human body?

Largest number electrical injury (60-70%) occurs in electrical installations up to 1000V. This is due to the wide distribution of these electrical installations and the relatively low level of electrical training of persons operating them.

The reasons:

touching non-insulated live parts;

touching metal non-current-carrying parts of electrical equipment that are energized;

touching non-metallic objects that are energized;

electric shock of step voltage or touch voltage;

defeat through the arc.

The degree of dangerous or harmful effects of electric current on a person depends on the parameters of the current flowing through the human body, the duration of exposure, environmental conditions and the state of the body (mass, physical condition).

For women, the threshold current values ​​are 1.5 times lower than for men.

The resistance of the human body is from 0.8 to 100 kOhm. Depends on the condition of the skin (wet, dry, clean or dirty).

The air environment in many cases affects the numerical values ​​of the damaging parameters of the electrical circuit in which a person finds himself. These are: atmospheric pressure, temperature, humidity, season, altitude, value electro magnetic field, constantly acting on a person (value electric field- 120 - 150 V / m, and even more in the thunderstorm and pre-storm period).

Currents in the frequency range from 5 to 500 Hz are almost equally dangerous. FROM further increase frequency values ​​of the threshold currents increase. A noticeable decrease in the risk of human injury - at a frequency above 1000 Hz (but the effect of the electric field increases).

Direct current up to 110 V is less dangerous than alternating current. Threshold values ​​of direct current are 3 - 4 times higher than at a frequency of 50 Hz. 150 - 600 V - the danger is about the same.

Over 600 V - alternating current is more dangerous. It is explained by physiological processes of influence on a living cell.

The degree of danger is affected by the composition of the air, the nature of the environment (room category).

The human body reacts to following currents:

Response current, mA DC current, mA

Tangible (itching and heat) 0.6 - 1.5 5 - 7

Not letting go 8 - 10

Respiratory contraction 25 - 50

muscles, suffocation

fibrillatory

(cardiac arrest) 80 - 100 (50 - 200)

Suffocation, paralysis, severe More than 500

burn, death.

Electric current, electric arc, electromagnetic or electrostatic field can produce damaging effect different nature:

Thermal - heating of tissues, burns;

Electrolytic - decomposition of tissues, blood;

Biological - irritation and excitation of living tissues, muscle contraction;

Light - the effect of an electric arc on the eyes, skin;

Mechanical - damage as a result of convulsive muscle contraction or falling from a height (ruptures of the skin, blood vessels, dislocations, fractures).

There are the following electrical injury:

electrical burns,

electrical signs,

electrometallization of the skin,

Electric shock.

electrical burns There are four degrees, like any other burns. They arise as a result of heating body tissues with a current of more than 1A. There are superficial and internal:

1st degree - redness, swelling of the skin;

2nd degree - water bubbles;

3rd degree - necrosis of the deep layers of the skin;

4th degree - charring of the skin, damage to muscles, tendons and bones.

electrical signs- spots of gray or pale yellow color in the form of corns on the surface of the skin as a result of thermal exposure at the point of contact with current-carrying parts. They are painless and go away with time.

Leather plating- penetration into the upper layers of the skin of the smallest particles of molten or splashed (as a result of an arc) metal. Color grey. The skin becomes rough and painful. It passes over time. Metallization of the eyes is a great danger. Inflammation of the eyes (electrophthalmia) - as a result of exposure to ultraviolet rays of an electric arc.

electric shock- electrocution of the body as a whole, causing a violation of physiological processes in it. Manifested in convulsive muscle contraction:

without loss of consciousness;

with loss of consciousness without violation of the functions of cardiac activity and respiration;

with loss of consciousness and dysfunction of cardiac activity and respiration;

clinical death.

Can thus lead to death by asphyxiation (respiratory muscle spasms), cardiac arrest or fibrillation. Clinical death lasting more than 10 minutes leads to irreversible consequences.

Electromagnetic field has harmful biological and electrolytic effects.

The most dangerous is the electrical component of the electromagnetic field. Failure of natural processes in the body, since dipole molecules (water) line up along the field lines of force.

On outdoor switchgear and overhead lines with a voltage of 330 kV and above, if the strength of the email. fields greater than 5 kV/m, the use of protective equipment is extremely important.

At E< 5 кВ/м ограничений при работе в электроустановках нет.

The possibility of human exposure to electrical discharges should be excluded.

The strength and induction of the magnetic field are also limited. So the allowable residence time is no more than 1 hour at H = 1600 A / m or B = 200 μT; no more than 8 hours at H = 80 A/m or B = 100 µT.

Why is electric current dangerous and what effect does it have on the human body? - concept and types. Classification and features of the category "How dangerous is electric current and what effect does it have on the human body?" 2017, 2018.

4.6.1. Electric current is a danger that does not warn of its presence (no visible moving parts, glow, noise, smell, etc.), but in the event of damage to electrical installations (violation of insulation strength, lack of grounding, incorrect execution, wire breakage etc.) a dangerous electric field arises around the fault in the area up to 20 m.

4.6.2. It is especially dangerous for a person to touch live parts that are energized.

4.6.3. According to the conditions of the danger of electric shock and for reasons of technical operation, electrical installations are divided into electrical installations with a supply voltage of up to 1000 V and above 1000 V.

4.6.4. The effect of electric current on the human body is complex and diverse:

Thermal (thermal) action is manifested in burns of the skin, individual parts of the body and heating of blood vessels, nerves, muscles, heart, brain and other organs to high temperatures. Burns occur when a person directly touches live parts and when an electric arc enters the zone (arc temperature is above 3500 ° C). They can be superficial or deep, accompanied by damage not only to the skin, but also to subcutaneous tissue, fat, deep-lying muscles, nerves and bones;

Electrolytic (biochemical) action is manifested in the decomposition (electrolysis) of blood, lymph and other organic fluids and causes significant violations of their physico-chemical composition, which in turn can lead to death;

The biological effect is manifested as irritation and excitation of the living tissues of the body, which is accompanied by involuntary convulsive muscle contractions, including the lungs and heart, a violation of internal bioelectric processes. As a result, there may be various violations and complete cessation of the activity of the circulatory and respiratory organs;

The mechanical action is expressed in the rupture of body tissues (mainly muscle), the walls of blood vessels, lung tissue, and some internal organs as a result of the electrodynamic effect. Mechanical damage can also be caused by a person falling from a height due to fright with a slight impact of current strength, which is practically safe if safety measures were not taken when working at height.

4.6.5. There are two main types of human electric shock electric shock and electric trauma.

Electric shock is the defeat of the body by electric current, in which the excitation of living tissues is accompanied by convulsive muscle contraction. In the worst case, an electric shock leads to a complete cessation of the activity of vital organs and death, while a person may not have external local injuries. Electric shocks are divided into:

1 degree - convulsive muscle contraction without loss of consciousness;

Grade 2 - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;

3 degree - loss of consciousness and impaired cardiac activity or breathing (or both);

4 degree - the state of clinical death (transitional period from life to biological death, occurring from the moment the heart stops working and breathing stops);

biological death.

An electrical injury is such an action of an electric current on the human body, in which tissues and internal organs of a person (skin, muscles, ligaments, bones, etc.) are damaged. Electrical injuries include:

Electric burn - the result of the thermal effects of an electric arc and electric current at the point of contact;

Electric sign - the result of superficial disorders of the skin and lymphatic tract, is a clearly defined spots on the skin of gray or gray-yellow color, expressed in hardening and necrosis of the upper layer;

Metallization of the skin - penetration into the upper layers of the skin of the smallest particles of metal during the burning of the arc. The color of the affected areas of the skin is determined by the color of the current conductor metal: green - in contact with copper, gray - with aluminum;

Electrophthalmia - inflammation of the outer membranes of the eyes as a result of exposure to powerful ultraviolet radiation when an electric arc occurs;

Mechanical damage (bruises, ruptures of the skin, blood vessels, ligaments, nerve tissues, dislocations and fractures of bones, etc.) arising from sudden involuntary movements (muscle contractions) of a person when exposed to electric current. Possible secondary consequences caused by a fall from a height, involuntary impacts.

4.6.6. Immediate causes The deaths of a person as a result of electric shock are the cessation of the heart, respiratory arrest and electric shock.

4.6.7. Electric shock is a kind of severe neuro-reflex reaction of the body to strong irritation with an electric current, accompanied by deep disorders of blood circulation, respiration, metabolism, etc. The state of shock lasts from several tens of minutes to a day. After that, a full recovery may occur as a result of timely therapeutic intervention or the death of the body due to the complete extinction of vital functions.

4.6.8. Factors that determine the degree of electric shock to a person:

Parameters of the electric current flowing through the human body (value, frequency, type of current - AC or DC);

Duration of current exposure;

The resistance of the human body: the resistance of the dry superficial skin is the highest, the resistance of the inner layers of the skin, saturated with blood vessels, glands and nerve endings, muscle, fat, bone tissues, blood and cerebrospinal fluid is small. Damage to the cornea of ​​​​the skin (cuts, scratches, abrasions), moisturizing the skin with water or sweat reduces the resistance of the human body, which proportionally increases the risk of electric shock;

Loop (passage path) of the current arm-arm, arm-leg, leg-leg, neck-leg, head-leg, head-arm, etc. All loops, except leg-leg, are called "large" or "full" loops , they are the most dangerous, because. current passes through vital organs: heart, lungs, brain. The leg-leg loop is called "small", only 0.4% of the total current flows through the heart. This loop occurs when a person is in the zone of current spreading, falling under step voltage;

The state of the human body (state of health, state of alcoholic intoxication, age). Physically healthy and strong people tolerate electric shocks more easily. Persons suffering from diseases of the skin, internal organs, lungs, cardiovascular diseases, etc. are distinguished by increased susceptibility to electric current;

Environmental conditions: dampness, conductive dust, conductive floors, closely spaced metal structures connected to the ground, high ambient temperature increase the risk of electric shock;

Psychological readiness to strike.

4.6.9. The main factors that determine the outcome of an electric shock are the strength of the current passing through the human body and its duration.

When a current of 0.6 ... 1.5 mA passes through the human body at an alternating 50 Hz and 5 ... 7 mA at a constant voltage in the hands, at the point of contact with current-carrying parts, an irritating effect, itching, tingling and heating are felt. This current strength is called the threshold of sensible current. The permissible duration of this current flow through a person is no more than 10 minutes.

An increase in current to 10 ... 15 mA at an alternating 50 Hz and up to 50 ... 60 mA at a constant voltage causes a person severe pain in the fingers, hands, muscles and their involuntary contraction. With this current strength, a person can still independently break away from current-carrying parts. This current strength is called the threshold of non-letting current. The duration of exposure to such a current is limited by the protective reaction of the person himself.

A further increase in the current strength above 10 ... 15 mA at an alternating 50 Hz and above 50 ... 60 mA at a constant voltage causes very severe pain, hands become paralyzed, respiratory paralysis sets in, a person cannot independently tear himself away from current-carrying parts.

When the current strength reaches 100 mA at an alternating 50 Hz and 300 mA at a constant voltage, cardiac fibrillation occurs (a scattered and uncoordinated contraction of individual groups of muscle fibers of the heart muscle, as a result of which the heart loses the ability to make coordinated contractions) and then it stops (clinical death). This current strength is called the fibrillation current threshold. With a short-term exposure (0.1 ... 0.5 sec.), This current does not cause heart fibrillation. If you increase the duration of exposure to 1 ... 2 seconds, then the same current can lead to death.

With a decrease in the duration of exposure, the values ​​\u200b\u200bof the currents permissible for a person increase significantly. So, when changing the exposure time from 1 to 0.1 sec. the allowable current will increase by about 16 times.

A current of more than 5 A does not cause fibrillation of the heart; at such currents, it instantly stops.

At voltages up to 400 V, alternating current with a frequency of 50 Hz is more dangerous than direct current. In the voltage range of 400 ... 600 V, the danger of direct current is almost equal to the danger of alternating current with a frequency of 50 Hz, and at a voltage of more than 600 V, direct current is more dangerous than alternating current due to its electrolytic effect. When exposed to direct voltage, especially sharp pain sensations occur at the moment of closing and opening the electrical circuit.

Table 3

Current Thresholds

4.6.10. The occurrence of electrical injuries is most often due to the following reasons:

Accidental contact with the current-carrying parts of electrical installations, or approaching them at distances less than permissible;

The appearance of voltage on metal non-current-carrying parts of installations as a result of damage to their insulation;

The appearance of voltage on disconnected current-carrying parts due to either accidental (erroneous) switching on of the installation, or reverse transformation;

The occurrence of step voltage as a result of the short circuit of the wire (phase) to the ground and the appearance of a potential difference between two points on the ground at a step distance;

The action of atmospheric electricity during lightning discharges or discharges due to the accumulation of static electricity;

Releasing another person under tension.

Similar information.

Why is electric current dangerous? How electric current affects a person

Fact of action electric current per person was set in the last quarter XVIII 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, which manifests itself in disruption of the normal activity of the cardiovascular and nervous systems, respiration, etc. A person can receive an electrical injury both by direct contact with current-carrying parts, and in case of damage by 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. The largest number of electrical injuries (60-70%) occurs 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. In a state of 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 excitation phase of the body begins: a reaction to pain appears, blood pressure rises, etc. Then the inhibition phase begins: 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 action of a current of the same strength 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 right hand- 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 hand- 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 due to the physiological processes of action on a living cell.

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