The effect of electric current on humans. Actions of electric current: thermal, chemical, magnetic, light and mechanical

Electric current has thermal, electrolytic, biological and mechanical effects on humans.

Thermal exposure to current manifested by burns of individual parts of the body, heating of organs to a high temperature, which causes significant functional disorders in them.

Electrolytic the impact of the decomposition of various body fluids (water, blood, lymph) into ions, resulting in a violation of their physical and chemical composition and properties.

Biological the effect of the current manifests itself in the form of irritation and excitation of body tissues, convulsive muscle contractions, as well as disruption of internal biological processes.

Mechanical the impact leads to delamination and rupture of body tissues.

The effect of electric current on a person leads to injury or death.

Electrical injuries are divided into general (electrical shocks) and local electrical injuries (Fig. 2.26).

The greatest danger comes from electrical shocks.

Electric shock- this is the excitation of living tissues by an electric current passing through a person, accompanied by convulsive muscle contractions; Depending on the outcome of the current, four degrees of electric shock are distinguished:

I - convulsive muscle contraction without loss of consciousness;

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

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

IV - clinical death, i.e. lack of breathing and blood circulation.

In addition to cardiac arrest and cessation of breathing, the cause of death may be electric shock - severe neuro-reflex reaction of the body to strong irritation by electric current. The state of shock lasts from several tens of minutes to a day, after which death or recovery may occur as a result of intensive therapeutic measures.

Rice. 2.26. Classification of electrical injuries

Local electrical injuries are local violations of the integrity of body tissues. Local electrical injuries include:

- electrical burn - can be current or arc; electric burn is associated with the passage of current through the human body and is a consequence of the conversion of electrical energy into thermal energy (as a rule, it occurs at relatively low voltages of the electrical network); at high voltages of the electrical network, an electric arc can form between the current conductor and the human body, a more severe burn occurs - an arc burn, since the electric arc has a very high temperature - over 3500 ° C;

- electrical signs- spots of gray or pale yellow color on the surface of human skin, formed at the point of contact with the current conductor; As a rule, the signs have a round or oval shape with dimensions of 1-5 mm; this injury does not pose a serious danger and is quite
passes quickly;

- metallization of leather — penetration into the upper layers of the skin of the smallest particles of metal melted under the influence of electric arc; depending on the location of the injury, the injury can be very painful; over time, the affected skin comes off; damage to the eyes can result in deterioration or even loss of vision;

- electroophthalmia - inflammation of the outer membranes of the eyes under the influence of a stream of ultraviolet rays emitted by an electric arc; for this reason, you cannot look at the welding arc; the injury is accompanied by severe pain and pain in the eyes, temporary loss of vision; with severe damage, treatment can be complex and lengthy; You cannot look at an electric arc without special protective glasses or masks;

- mechanical damage arise as a result of sharp convulsive contractions of muscles under the influence of current passing through a person; with involuntary muscle contractions, ruptures of the skin, blood vessels, as well as dislocations of joints, ruptures of ligaments and even bone fractures can occur; In addition, when frightened and shocked, a person may fall from a height and be injured.

As you can see, electric current is very dangerous and handling it requires great care and knowledge of electrical safety measures.

Parameters that determine the severity of electric shock(Fig. 2.27). The main factors that determine the degree of electric shock are: the strength of the current flowing through the person, the frequency of the current, the time of exposure and the path of the current through the person's body.

Current strength. Flow through the body AC industrial frequency (50 Hz), widely used in industry and in everyday life, a person begins to feel at a current strength of 0.6... 1.5 mA (mA - milliampere is 0.001 A). This current is called threshold perceptible current.

Large currents cause painful sensations in a person, which intensify with increasing current. For example, with a current of 3...5 mA, the irritating effect of the current is felt by the entire hand, with 8...10 mA - a sharp pain covers the entire arm and is accompanied by convulsive contractions of the muscles of the hand and forearm.

At 10...15 mA, arm muscle spasms become so strong that a person cannot overcome them and free himself from the current conductor. This current is called threshold non-releasing current.

With a current of 25...50 mA, disturbances occur in the functioning of the lungs and heart; with prolonged exposure to such a current, cardiac arrest and cessation of breathing can occur.

Rice. 2.27. Parameters that determine the severity of electric shock

Starting from size 100 mA the flow of current through a person causes fibrillation hearts- convulsive irregular contractions of the heart; the heart stops working as a pump pumping blood. This current is called threshold fibrillation current. A current of more than 5A causes immediate cardiac arrest, bypassing the state of fibrillation.

Current frequency. The most dangerous current at industrial frequency is 50 Hz. Direct current and current of high frequencies are less dangerous, and the threshold values ​​for it are higher.

So, for direct current:

Threshold perceptible current - 5...7 mA;

Threshold non-releasing current - 50...80 mA;

Fibrillation current - 300 mA.

Current Flow Path. The danger of electric shock depends on the path the current flows through the human body, since the path determines the proportion of the total current that passes through the heart. The most dangerous path " right hand“legs” (a person most often works with his right hand). Then, according to the degree of danger reduction, there are: “left arm-legs”, “arm-arm”, “legs-legs”. In Fig. Figure 2.28 shows possible paths for current flow through a person.

Rice. 2.28. Characteristic current paths in the human body: 1 — hand-hand; 2 - right arm and legs; 3 - left arm and legs; 4 — right arm-right leg; 5 - right hand - left leg; 6 - left hand-left leg; 7 - left hand-right leg; 8 — both arms, both legs; 9 — leg-leg; 10 - head-hands; 11 — head-legs; 12 — head-right hand: 13 - head-left hand; 14 — head-right leg; 15 - head-left leg

Electric current exposure time. The longer the current flows through a person, the more dangerous it is. When electric current flows through a person at the point of contact with the conductor, the top layer of skin (epidermis) is quickly destroyed, electrical resistance body decreases, the current increases, and the negative effect of the electric current is aggravated. In addition, over time, the negative consequences of the influence of current on the body grow (accumulate).

The determining role in the damaging effect of current is played by the magnitude of the electric current, flowing through the human body. Electric current occurs when a closed electrical circuit is created in which a person is included. According to Ohm's law, the strength of electric current / is equal to electric voltage U, divided by resistance electrical circuit R:1=U/R.

Thus, the higher the voltage, the larger and more dangerous the electric current. The greater the electrical resistance of the circuit, the less the current and the danger of injury to a person.

Electrical resistance of the circuit equal to the sum of the resistances of all sections that make up the circuit (conductors, floor, shoes, etc.). The total electrical resistance necessarily includes the resistance of the human body.

Electrical resistance of the human body with dry, clean and intact skin, it can vary within a fairly wide range - from 3 to 100 kOhm (1 kOhm = 1000 Ohm), and sometimes more. The main contribution to the electrical resistance of a person is made by the outer layer of skin - epidermis, consisting of keratinized cells. The resistance of the internal tissues of the body is not large - only 300...500 Ohms.

Therefore, with delicate, moist and sweaty skin or damage to the epidermis (abrasions, wounds), the electrical resistance of the body can be very small. A person with such skin is most vulnerable to electric current. Girls have more delicate skin and a thin layer of epidermis than boys; In men with calloused hands, the electrical resistance of the body can reach very high values, and the danger of electric shock is reduced. In calculations for electrical safety, the resistance value of the human body is usually taken to be 1000 Ohms.

Electrical insulation resistance current conductors, if it is not damaged, is, as a rule, 100 or more kilo-ohms.

Electrical resistance of shoes and base (floor) depends on the material from which the base and sole of the shoe are made, and their condition - dry or wet (wet). For example, a dry sole made of leather has a resistance of approximately 100 kOhm, a wet sole - 0.5 kOhm; made of rubber, respectively 500 and 1.5 kOhm. A dry asphalt floor has a resistance of about 2000 kOhm, a wet one - 0.8 kOhm; concrete 2000 and 0.1 kOhm, respectively; wooden - 30 and 0.3 kOhm; earth - 20 and 0.3 kOhm; from ceramic tiles- 25 and 0.3 kOhm. As you can see, with damp or wet bases and shoes, the electrical hazard increases significantly.

Therefore, when using electricity in wet weather, especially on water, it is necessary to take special care and take increased measures to ensure electrical safety.

For lighting, household electrical appliances, and a large number of devices and equipment in production, a voltage of 220 V is usually used. There are electrical networks with 380, 660 or more volts; Many technical devices use voltages of tens and hundreds of thousands of volts. Such technical devices pose an exceptionally high danger. But significantly lower voltages (220, 36 and even 12 V) can be dangerous depending on the conditions and the electrical resistance of the circuit R..

Individual characteristics of a person have a significant impact on the outcome of damage due to electrical injuries.

The nature of the effect of current (table) depends on the mass of the person and his physical condition. Healthy and physically strong people can more easily withstand electric shocks. Increased susceptibility to electric current has been noted in persons suffering from diseases of the skin, cardiovascular system, internal secretion organs, nervous system, etc.

Table The nature of the current effect

People who sweat excessively are more vulnerable to the effects of electric current. Elevated ambient temperature and high humidity are not the only cause of excessive sweating; intense sweating is often observed in autonomic disorders of the nervous system, as well as as a result of fear and excitement.

In a state of excitement of the nervous system, depression, fatigue, intoxication and after it, people are more sensitive to the flowing current.

Maximum permissible touch voltages and currents for humans are established by GOST 12.1.038-82* (Table 2.14) during emergency operation of electrical installations DC frequency 50 and 400 Hz. For an alternating current with a frequency of 50 Hz, the permissible value of the touch voltage is 2 V, and the current strength is 0.3 mA, for a current with a frequency of 400 Hz, respectively, 2 V and 0.4 mA; for direct current - 8 V ​​and 1 mA. The specified data are given for a duration of exposure to current of no more than 10 minutes per day.

Table 2.14. Extremely permissible levels voltage and current

Analysis of circuits for connecting a person to an electrical circuit

Since from the resistance of the electrical circuit R Since the magnitude of the electric current passing through a person significantly depends, the severity of the injury is largely determined by the scheme of connecting the person to the circuit. The patterns of circuits formed when a person comes into contact with a conductor depend on the type of power supply system used.

The most common electrical networks are those in which the neutral wire is grounded, i.e., short-circuited by a conductor to the ground. Touching the neutral wire poses virtually no danger to humans; only the phase wire is dangerous. However, it is difficult to figure out which of the two wires is neutral - they look the same. You can figure it out using a special device - a phase detector.

On specific examples Let's consider possible schemes for connecting a person to an electrical circuit when touching conductors.

Two-phase connection to the circuit. The rarest, but also the most dangerous, is a person touching two phase wires or current conductors connected to them (Fig. 2.29).

In this case, the person will be under the influence of line voltage. A current will flow through a person along the “hand-to-hand” path, i. e. circuit resistance will only include body resistance (I).

Rice. 2.29. Two-phase connection to the circuit: A— isolated neutral; b- grounded neutral

If we assume a body resistance of 1 kOhm, and an electrical network with a voltage of 380/220 V, then the current strength passing through a person will be equal to

I h = U l / R h= 380 V / 1000 Ohm = 0.38 A = 380 mA.

It's deadly dangerous current. The severity of an electrical injury or even a person’s life will depend primarily on how quickly he frees himself from contact with the current conductor (breaks the electrical circuit), because the time of exposure in this case is decisive.

Much more often there are cases when a person comes into contact with a phase wire or part of a device with one hand, a device that is accidentally or intentionally electrically connected to it. The danger of electric shock in this case depends on the type of electrical network (with grounded or insulated neutral).

Single-phase connection to a circuit in a network with a grounded neutral(Fig. 2.30). In this case, the current passes through the person along the “arm-legs” or “arm-arm” path, and the person will be under phase voltage.

In the first case, the circuit resistance will be determined by the resistance of the human body (R h, shoes (R o 6), grounds (R oc), on which a person stands, the neutral grounding resistance ( R n), and current will flow through the person

I h = U f /(R h + R o b + R 0 C + R n).

Neutral resistance RH is small and can be neglected compared to other circuit resistances. To estimate the magnitude of the current flowing through a person, we will take the network voltage to be 380/220 V. If a person is wearing insulating dry shoes (leather, rubber), he is standing on a dry wooden floor, the circuit resistance will be large, and the current strength according to Ohm’s law is small.

For example, floor resistance is 30 kOhm, leather shoes are 100 kOhm, human resistance is 1 kOhm. Current passing through a person

I h = 220 V / (30,000 + 100,000 + 1000) Ohm = = 0.00168 A = 1.68 mA.

This current is close to the threshold perceptible current. The person will feel the flow of current, stop working, and eliminate the malfunction.

If a person stands on wet ground with damp shoes or barefoot, a current will pass through the body

I H= 220 V / (3000 + 1000) Ohm = 0.055 A = 55 mA.

This current can cause damage to the lungs and heart, and with prolonged exposure, death.

If a person stands on wet soil wearing dry and intact rubber boots, a current passes through the body

I h = 220 V / (500,000 + 1000) Ohm = 0.0004 A = 0.4 mA.

A person may not even feel the impact of such a current. However, even a small crack or puncture in the sole of a boot can dramatically reduce the resistance of the rubber sole and make work dangerous.

Before you start working with electrical devices(especially those not in use for a long time), they must be carefully inspected to ensure there is no damage to the insulation. Electrical devices must be wiped from dust and, if they are wet, dried. Wet electrical devices must not be used! Electric tool, devices, equipment is best stored in plastic bags to prevent dust or moisture from getting into them. You have to wear shoes when working. If the reliability of an electrical device is in doubt, you need to be on the safe side - place a dry one under your feet. wood flooring or rubber mat. You can use rubber gloves.

Rice. 2.30. Single-phase touch in a network with a grounded neutral: A— normal operating mode; b — emergency operation mode (second phase damaged)

The second path of current flow occurs when a person comes into contact with electrically conductive objects connected to the ground with his second hand (the body of a grounded machine, metal or reinforced concrete structure buildings, damp wooden wall, water pipe, heating battery, etc.). In this case, the current flows along the path of least electrical resistance. These objects are practically short-circuited to the ground, their electrical resistance is very small. Therefore, the resistance of the circuit is equal to the resistance of the body and current will flow through the person

I h = U F / R H= 220 V / 1000 Ohm = 0.22 A = 220 mA.

This amount of current is deadly.

When working with electrical devices, do not use your other hand to touch objects that may be electrically connected to ground. Work in damp areas, if there are highly conductive objects connected to the ground near a person, it poses an extremely high danger and requires compliance with increased electrical safety measures.

In emergency mode (Fig. 2.30, b), when one of the phases of the network (another phase of the network, different from the phase touched by a person) is shorted to ground, voltage redistribution occurs, and the voltage of the healthy phases differs from the phase voltage of the network. When touching a working phase, a person comes under voltage that is greater than the phase voltage, but less than the linear one. Therefore, regardless of the path of current flow, this case is more dangerous.

Single-phase connection to a circuit in a network with an isolated neutral(Fig. 2.31). In production, three-wire electrical networks with an insulated neutral are used to supply power electrical installations. In such networks there is no fourth grounded neutral wire, and there are only three phase wires. In this diagram, rectangles conventionally show electrical resistance g A, g c, g c insulation of wires of each phase and tank S A, S v, S s each phase relative to ground. To simplify the analysis, let us assume r A = r B =r c =r, l S A= C £ = C c = C

Rice. 2.31. Single-phase touch in a network with an isolated neutral: A - normal operating mode; b— emergency operation (second phase damaged)

If a person touches one of the wires or any object electrically connected to it, current will flow through the person, shoes, base and through the insulation and capacitance of the wires will flow to the other two wires. Thus, a closed electrical circuit is formed, in which, unlike the previously considered cases, the phase insulation resistance is included. Since the electrical resistance of working insulation is tens and hundreds of kilo-ohms, the total electrical resistance of the circuit is much greater than the resistance of the circuit formed in a network with a grounded neutral wire. That is, the current through a person in such a network will be less, and touching one of the phases of the network with an isolated neutral is safer.

The current through a person in this case is determined by the following formula:

Where R ich = R h + R rev + R os— electrical resistance of a human circuit, ω = 2π f— circular current frequency, rad/s (for industrial frequency current f= 50 Hz, so ω = 100π).

If the phase capacity is small (this is the case for short air networks), you can take C ≈ 0. Then the expression for the magnitude of the current through a person will take the form:

For example, if the floor resistance is 30 kOhm, leather shoes are 100 kOhm, the human resistance is 1 kOhm, and the phase insulation resistance is 300 kOhm, the current that passes through the person (for a 380/220 V network) will be equal to

I h= 3 ? 220 V / Ohm = = 0.00095 A = 0.95 mA.

A person may not even feel such a current.

Even if we do not take into account the resistance of the human circuit (the person is standing on wet ground in damp shoes), the current passing through the person will be safe:

I h = 3? 220 V / 300,000 Ohm = 0.0022 A = 2.2 mA.

Thus, good insulation phases is the key to ensuring safety. However, with extensive electrical networks, this is not easy to achieve. In long and branched networks with a large number of consumers, the insulation resistance is low, and the danger increases.

For extended electrical networks, especially cable lines, the phase capacitance cannot be neglected (C≠0). Even with very good phase insulation (r =∞) current will flow through the person through the capacitance of the phases, and its value will be determined by the formula:

I h =

Thus, long electrical circuits of industrial enterprises with high capacitance are highly dangerous, even with good phase insulation.

If the insulation of any phase is broken, touching a network with an isolated neutral becomes more dangerous than touching a network with a grounded neutral wire. In emergency mode (Fig. 2.31, b) the current passing through a person who has touched the serviceable phase will flow through the ground fault circuit to the emergency phase, and its value will be determined by the formula:

I h = U l / (R ich + R s).

Since the circuit resistance R z emergency phase on earth is usually small, then the person will be under linear voltage, and the resistance of the resulting circuit will be equal to the resistance of the human circuit R z, which is very dangerous.

For these reasons, as well as because of ease of use (the ability to obtain voltages of 220 and 380 V), four-wire networks with a grounded neutral wire for a voltage of 380/220 V have become most widespread.

We have not considered all possible electrical network diagrams and touch options. In production, you may be dealing with more complex power supply circuits that are under significantly higher voltages, and therefore more dangerous. However, the main conclusions and recommendations for ensuring safety are almost the same.

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 impact 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.

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 effects 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 is increased, unpleasant problems appear. painful sensations, 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 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 muscle and organ spasms, disruption of organ activity, up to 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.:

• Signs - have an oval shape and appear on the skin in the form of spots of pale yellow or gray. 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 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 looking defeats.

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, as well as the functioning of the heart is impaired.

Fourth degree– human exposure to electricity with very great strength current, in 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.

So, working with electrical appliances should only be carried out 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.

If this is not possible, you need to pull the person away from the source, but you cannot touch the body; you need to pull him by his clothes.

If, as a result of muscle paralysis, the victim’s hand compresses the wire with the source, you should first cut the wire with a sharp object with a non-conductive handle, for example, an ax with a dry wooden handle.

After breaking contact, first aid must be provided. If a person is conscious, he needs to be provided with a comfortable position for rest.

In case of loss of consciousness, but maintaining breathing, provide him with a comfortable position, unfasten the collar to ensure air flow, use ammonia to bring you to your senses.

When clinical death occurs, when there is no breathing and no heartbeat, you should try to bring him out of this state by performing artificial respiration and cardiac massage. And of course, don’t forget to call an ambulance.

The effect of electric current on the human body is complex and versatile. Passing through the human body, electric current produces thermal, electrolytic and biological effects.

The thermal effect of the current manifests itself in burns of individual parts of the body, as well as in heating other organs to high temperatures.

The electrolytic effect of current is expressed in the decomposition of organic liquids, causing significant disturbances in their physical and chemical composition.

The biological effect of current is manifested in irritation and excitation of living tissues of the body, as well as in disruption of internal bioelectric processes.

What types of electrical injuries can be divided into?

Electrical injuries can be divided into two types: local electrical injuries and electrical shocks.

Local electrical injuries are understood as clearly defined local violations of the integrity of body tissues. Most often these are superficial injuries, i.e. damage to the skin, and sometimes other soft tissues, as well as ligaments and bones. Typically, local electrical injuries are cured and performance is restored fully or partially. Sometimes (with severe burns) a person dies. The immediate cause of death is not the electric current (or arc), but the local damage to the body caused by the current (arc). Typical types of local electrical injuries are electrical burns, electrical marks, skin metallization, electroophthalmia and mechanical damage.

What is an electrical burn?

Electrical burns are the most common electrical injuries: they occur in the majority of victims (60-65%), and about a third of them are accompanied by other electrical injuries.

There are two types of burns: current (or contact) and arc. Electrical burn occurs as a result of human contact with a live part and is a consequence of the conversion of electrical energy into thermal energy. These burns occur in electrical installations of relatively low voltage - no higher than 1-2 kV, and in most cases they are relatively mild.

An arc burn is caused by exposure to an electric arc on the body, which has high temperature And great energy. This burn usually occurs in electrical installations with voltages above 1 kV and is usually severe. An electric arc can cause extensive burns to the body, deep burns of tissue, and permanent burning of large areas of the body.

What are the characteristics of electrical signs?

Electrical marks (current marks or electrical marks) are clearly defined gray or pale yellow spots on the surface of the skin of a person exposed to current. The signs are round or oval in shape with a depression in the center. They come in the form of scratches, small wounds or bruises, warts, hemorrhages in the skin and calluses. Sometimes their shape matches the shape of the live part that the victim touched, and also resembles the shape of a moth.

In most cases, electric signs are painless, and their treatment ends well: over time, the top layer of skin and the affected area regain their original color, elasticity and sensitivity. Signs occur in approximately 20% of electric shock victims.

What is leather metallization?

Metallization of the skin is the penetration into its upper layers of the smallest particles of metal melted under the action of an electric arc. This can happen due to short circuits, disconnectors and circuit breakers tripping under load, etc. The victim at the site of the injury experiences skin tension from the presence of a foreign body in it and pain from a burn due to the heat of the metal brought into the skin. Over time, the diseased skin disappears, the affected area takes on a normal appearance and the painful sensations disappear. If the eyes are affected, treatment can be lengthy and difficult.

Metallization of the skin is observed in approximately 10% of victims.

What are the conditions for the occurrence of electroophthalmia?

Electroophthalmia is an inflammation of the outer membranes of the eyes that occurs as a result of exposure to a powerful stream of ultraviolet rays, which are vigorously absorbed by the body's cells and cause chemical changes in them. Such irradiation is possible in the presence of an electric arc (for example, during a short circuit), which is a source of intense radiation not only of visible light, but also of ultraviolet and infrared rays.

Electroophthalmia occurs relatively rarely - in 1-2% of victims.

What are the characteristics of mechanical damage?

Mechanical damage occurs as a result of sudden, involuntary, convulsive muscle contractions under the influence of current passing through the human body. This can result in ruptured skin, blood vessels, and nerve tissue, as well as dislocated joints and broken bones. Mechanical injuries are usually serious injuries that require long-term treatment. They occur relatively rarely.

What is an electric shock?

An electric shock is the stimulation of living tissues of the body by an electric current passing through it, accompanied by muscle contractions. The outcome of the effect of current on the body can be different - from a slight, barely perceptible convulsive contraction of the muscles of the fingers to the cessation of the heart or lungs, i.e., to fatal injury.

Electrical shocks can be divided into four degrees:

• I - convulsive muscle contraction without loss of consciousness;
• II - convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;
• III - loss of consciousness and disturbance of cardiac activity or breathing (or both);
• IV - clinical death, i.e. lack of breathing and blood circulation.

What is clinical (imaginary) death characterized by?

Clinical (imaginary) death is a transition period from life to death, occurring from the moment the activity of the heart and lungs ceases.

A person in a state of clinical death does not breathe, his heart does not work, painful stimuli do not cause any reactions, the pupils of the eyes are dilated and do not react to light. However, during this period, weak metabolic processes still continue in almost all tissues of the body, sufficient to maintain minimal vital activity.

During clinical death, the cells of the cerebral cortex, sensitive to oxygen starvation, the activities of which are associated with consciousness and thinking, are the first to die. Therefore, the duration of clinical death is determined by the time from the moment of cessation of cardiac activity and breathing until the beginning of the death of cells in the cerebral cortex: in most cases it is 4-5 minutes, and in case of death healthy person from an accidental cause, for example from an electric current, - 7-8 minutes. In a state of clinical death, by influencing the respiratory and circulatory organs, it is possible to restore fading or just extinct functions, i.e., revive the dying organism.

What is biological (true) death?

Biological death is understood as an irreversible phenomenon characterized by the cessation of biological processes in the cells and tissues of the body and the breakdown of protein structures. It occurs after clinical death.

Causes of death from electric current can be: cessation of heart function, breathing and electric shock.

What causes the heart to stop working?

The cessation of heart function is the result of the direct effect of current on the heart muscle, i.e., the passage of current directly into the region of the heart, and sometimes the result of a reflex action. In both cases, cardiac arrest or fibrillation may occur.

What is fibrillation?

Fibrillation is chaotic and multi-temporal contractions of cardiac muscle fibers (fibrils), in which the heart ceases to function as a pump, i.e., it is unable to ensure the movement of blood through the vessels. As a result, blood circulation in the body is disrupted and, as a result, the delivery of oxygen by blood from the lungs to the tissues and organs stops, which causes the death of the body.

What are the reasons for stopping breathing?

The cessation of breathing is caused by the direct and, in some cases, reflex effects of the current on the chest muscles involved in the breathing process. A person experiences difficulty breathing even with an alternating current of 20-25 mA, which intensifies with increasing current strength. With prolonged exposure to such a current (several minutes), asphyxia (suffocation) occurs as a result of a lack of oxygen and excess carbon dioxide in the body. Breathing also stops as a result of short-term (several seconds) exposure to a large current (several hundred milliamps).

What is electric shock characterized by?

Electric shock is a kind of severe neuroreflex reaction of the body in response to strong irritation by electric current. It is accompanied by dangerous disorders of blood circulation, breathing, metabolism, etc. The state of shock lasts from several minutes to a day. After this, either the death of the organism may occur as a result of complete extinction of vital important functions, or recovery after timely active therapeutic intervention.

What factors determine the risk of electric shock?

The danger of exposure to electric current on a person depends on the resistance of the human body and the magnitude of the voltage applied to it, the strength of the current passing through the body, the duration of its exposure, the path of passage^, the type and frequency of the current, the individual properties of the victim and factors environment.

What is the electrical resistance of the human body?

The human body is a conductor of electric current. Different tissues of the body offer different resistance to current: skin, bones, adipose tissue - high, and muscle tissue, blood and especially the spinal cord and brain - small. The skin and mainly its upper layer, called the epidermis, have the greatest resistance compared to other tissues.

The electrical resistance of the human body with dry, clean and intact skin at a voltage of 15-20 V ranges from 3000 to 100,000 Ohms, and sometimes more. When the entire top layer of skin is removed, the resistance drops to 500-700 Ohms. With complete removal of the skin, the resistance of the internal tissues of the body will be only 300-500 Ohms. When calculating, the resistance of the human body is usually assumed to be 1000 Ohms. In reality, this is a variable value, depending on many factors, including the condition of the skin, electrical circuit parameters, physiological factors and environmental conditions (humidity, temperature, etc.). The condition of the skin greatly affects the electrical resistance of the human body. Thus, damage to the stratum corneum, including cuts, scratches and other microtraumas, can reduce resistance to a value close to the value of internal resistance, thereby increasing the risk of electric shock to a person. The same effect is exerted by moisturizing the skin with water or sweat, as well as contamination with conductive dust and dirt.

Due to the different electrical resistance of the skin in different parts of the body, the resistance as a whole is influenced by the location of the contacts and their area.

The resistance of the human body decreases with an increase in the value of the current and the duration of its passage due to increased local heating of the skin, leading to vasodilation, and, consequently, to an increased supply of blood to this area and an increase in sweating.

An increase in voltage applied to the human body reduces the resistance of the skin tens of times, and therefore the total resistance of the body, which approaches its lowest value 300-500 Ohm. This is explained by the breakdown of the stratum corneum of the skin, an increase in the current passing through the skin, and other factors.

The type of current and frequency also affect the value of electrical resistance. At frequencies of 10-20 kHz, the outer layer of the skin practically loses its resistance to electric current.

How does the magnitude of the current affect the outcome of the injury?

The strength of the electric current passing through the human body is the main factor determining the outcome of the injury.

A person begins to feel the impact of an alternating current of 0.6-1.5 mA passing through him. This current is called threshold perceptible.

With a current of 10-15 mA, a person cannot take his hands off the electrical wires and independently break the circuit of the current striking him. Such a current is usually called non-releasing current. A current of a lower value is called releasing current.

A current of 50 mA affects the respiratory system and cardiovascular system. At 100 mA, cardiac fibrillation occurs, which consists of erratic, chaotic contraction and relaxation of the muscle fibers of the heart. It stops, blood circulation stops.

A current greater than 5 A, as a rule, does not cause cardiac fibrillation. With such currents, immediate cardiac arrest and respiratory paralysis occurs. If the effect of the current is short-term (up to 1-2 s) and does not cause damage to the heart (as a result of heating, burns, etc.), then after the current is turned off, the heart independently resumes normal activity, and immediate assistance in the form of artificial respiration is required to restore breathing .

What effect does the duration of current passage through the human body have on the outcome of the injury?

The longer the current, the greater the likelihood of a serious or fatal outcome. This dependence is explained by the fact that with increasing time of exposure of living tissue to current, the value of this current increases (due to a decrease in body resistance), the consequences of the influence of current on the body accumulate, and the likelihood of the moment of current passage through the heart coinciding with the T phase of the cardiac cycle, which is especially vulnerable to current, increases. (cardiocycle).

What is the significance of the current path in the victim’s body in the outcome of the injury?

If vital organs - the heart, lungs, brain - are in the path of the current, the danger of their damage is very high. If the current passes through other paths, then its effect on vital organs can be reflexive, that is, through the central nervous system, due to which the likelihood of a serious outcome is sharply reduced.

Since the path of the current depends on which parts of the body the victim touches the live parts, its influence on the outcome of the injury is also manifested because the skin resistance in different parts of the body is different. The most dangerous path is right hand - legs, the least dangerous is leg - leg.

How does the type and frequency of current affect the outcome of the lesion?

Direct current is approximately 4-5 times safer than 50 Hz alternating current. However, this is typical for relatively small voltages - up to 250-300 V. At higher voltages, the danger of direct current increases.

With an increase in the frequency of alternating current passing through the human body, the total resistance of the body decreases, and the magnitude of the passing current increases. However, a decrease in resistance is possible only within frequencies from 0 to 50-60 Hz; a further increase in frequency is accompanied by a decrease in the danger of injury, which completely disappears at a frequency of 450-500 kHz. But these currents retain the danger of burns both in the event of an electric arc and when they pass directly through the human body. The decrease in the risk of electric shock with increasing frequency becomes practically noticeable at a frequency of 1000-2000 Hz.

What is the influence of a person’s individual characteristics on the outcome of electric shock?

It has been established that healthy and physically strong people can withstand electric shocks more easily than sick and weak people. Persons suffering from a number of diseases, primarily diseases of the skin, cardiovascular system, internal secretion organs, nervous system, etc., have an increased susceptibility to electric current.

How does the external environment influence the mechanism of injury?

The presence of chemically active and toxic gases in the indoor air of a number of industries that enter the human body reduces the electrical resistance of the body. In humid and damp areas, the skin becomes moisturized, which significantly reduces its resistance. Moisture that enters the skin dissolves the minerals and fatty acids present on it, which are removed from the body along with sweat and sebum, so the skin becomes more electrically conductive.

When working in rooms with high ambient temperatures, the skin heats up and increased sweating occurs. Sweat is a good conductor of electric current. Consequently, working in such conditions increases the risk of exposure to electric current to a person. Recent studies have established that the amount of resistance of the human body in such conditions is significantly reduced. It depends both on the duration of stay in an environment with elevated temperature, and on the temperature of this environment and the intensity of thermal loads.

In some cases, the skin is contaminated with various substances that conduct electricity well, which reduces its resistance. People with such skin are at greater risk of electric shock.

In certain production areas, noise and vibrations arise that have a negative effect on the entire human body: increased blood pressure,

the breathing rhythm is disrupted. These factors, as well as deficiencies in lighting in a number of industries, cause a slowdown in mental reactions, a decrease in attention, which plays an important role in the erroneous actions of personnel and leads to accidents and accidents, including electrical injuries.

Are there any known cases of long-term consequences of electrical trauma?

Yes, they are known. Long after an electrical injury, cases of diabetes, diseases of the thyroid glands, and genital organs have been observed; various diseases allergic nature (urticaria, eczema, etc.), as well as persistent organic changes in the cardiovascular system and autonomic endocrine disorders.

Cases of late complications in the form of neuropsychic disorders (schizophrenia, hysteria, psychoneurosis, impotence), and the development of cataracts 3-6 months after electrical injuries have been described.

Electricians are more likely than other professions to develop early development of arteriosclerosis, endoarthritis, autonomic and other disorders.

Thus, the effect of electric current does not always pass without a trace and often leads to a decrease in working capacity, and sometimes to chronic diseases.

It is known that a person is unable to detect with his organs the presence of dangerous voltage, and the physiological processes constantly occurring in the body are incompatible with the flow of electric current through his body.

There are four types of current exposure:

Thermal;
- electrolytic;
- dynamic;
- biological.

Thermal impact- randomly shaped burns appear on the body after contact with electricity. When overheated, organs located in the path of the electric current temporarily lose their functionality. As a result of the lesion, both the brain and the circulatory or nervous systems can be damaged, leading to serious disorders.

Electrolytic effects- damage to the blood and lymph in the body, which leads to their breakdown and changes in physico-chemical composition.

Dynamic, or as it is also called mechanical, the impact causes damage to the structure of body tissues (including muscle, lung tissue, walls of blood vessels) in the form of dissection, lacerations, and in some cases even ruptures. Injury is caused by overheating of blood and tissue fluid with the instant release of steam, similar to an explosion.

Biological effects affects the muscular system and living tissues, leading to its temporary dysfunction. As a result, involuntary convulsions may occur. muscle contractions. This action, even temporary, can adversely affect the functioning of the heart or respiratory system, and death cannot be ruled out.

Types of electrical injuries:

Local in nature, when certain areas of the body are damaged;
- general damage - injuries caused by an electric shock to the entire body.

The ratios of electrical injuries, according to static studies, were distributed as follows:

20% - local manifestations;
- 25% - general damage to the body;
- 55% - mixed lesions.

Most often, accidents involving both types of injuries occur, but they should be treated as separate because they have significant differences.

Local electrical injuries. Damage to the body is associated with violations of the integrity of body tissues. Most often the skin is injured, but there are cases of damage to ligaments or bones.

The degree of risk of injury depends on the condition and location of the damaged tissue. In most cases, they are cured with complete restoration of the functionality of the affected part of the body.

About 75% of accidents from electric shock have a local damage zone and occur with the following frequency:

Electrical burns - ≈40%;
- electrical signs - ≈7%;
- metallization of the skin - ≈3%;
- mechanical damage – ≈0.5%
- cases of electroophthalmia - ≈1.5%;
- mixed injuries - ≈23%.

Electrical burns. Tissue damage occurs from the thermal effect of electric current, occurs frequently, and is divided into:

Current or contact, occurring when a person comes into contact with live equipment;
- arc, caused by the action of an electric arc.

Electrical burns are typical for electrical devices with voltages up to 2 kV. Electrical objects of higher voltage form an electric arc.

The severity of the burn depends on the power of the current and the duration of its passage. The skin burns quickly due to greater resistance than internal tissues. At increased frequencies, currents penetrate deep into the body and affect internal organs.

Arc burns occur when EI operates at different voltages. Moreover, sources up to 6 kV can form an arc in the event of an accidental short circuit. Higher voltages break through the resistance of the air insulation between a person and electrical equipment, reducing the safe gap to live parts.

Electric signs. These are oval-shaped spots of pale yellow or gray color located on the surface of the body. They are about 1-5 mm in size. They are easy to treat and do not cause much discomfort to a person.

It is damage to the skin by small particles of molten metal that penetrate into the upper layers of the skin from the arc during short circuits.

The most dangerous injury includes damage to the eye area. To prevent it, during work involving broken circuits and the simultaneous formation of an electric arc, the worker must use special safety glasses and completely cover the body with special clothing.

Mechanical damage. Most typical when working in electrical installations up to 1000 V under prolonged exposure to electric current.

Manifest in the form of involuntary muscle spasms, which can lead to rupture of skin, nerve tissue or blood vessels. There are cases of dislocation of joints and broken bones.

Electroophthalmia. Eye damage is associated with inflammatory processes of the outer membrane (conjunctiva and cornea) from exposure to a strong luminous flux of the ultraviolet spectrum of an electric arc.

For protection, you need to use glasses or a mask with colored special glasses.

Electric shock. The rapid, almost instantaneous formation of a current circuit in the body affects living tissues, leads to muscle cramps, and disrupts the functioning of all organs, especially the nervous system, heart and lungs. The degree of electric shock is determined in five stages:

1. Light contractions of individual muscles;
2. Muscle cramps that create pain while the victim is conscious;
3. Convulsive muscle contractions causing loss of consciousness while the heart and lungs continue to function;
4. The victim is unconscious, the rhythm/work of the heart and/or breathing is impaired;
5. Lethal outcome.

The consequences of an electric shock on the human body depend on a number of factors:

Duration and magnitude of damaging electric current;
- frequency and type of current;
- flow paths;
- individual capabilities of the affected organism.

Fibrillation. Cardiac muscle fibers (fibrils) under the influence of alternating current with a frequency of 50 Hz, exceeding 50 mA, begin chaotic contractions. After a few seconds, blood pumping stops completely. The body's blood flow stops.

The path for current through the heart is most often created by contacts between the arms or leg and arm. Smaller 50 mA and higher 5 A currents do not cause fibrillation of the heart muscle in humans.

Electric shock. An electric shock is difficult for the body to perceive and a neuro-reflex reaction occurs. The respiratory and nervous systems, blood circulation, and internal organs are affected.

After exposure to electric current, a phase of so-called excitation of the body begins: pain appears and blood pressure increases.

Then the body goes into a phase of inhibition: blood pressure decreases, the pulse becomes disrupted, the respiratory and nervous systems weaken, and depression sets in. The duration of this state can vary from several minutes to days.

Back in late XVIII century, the fact of the negative and dangerous effects of electric current on the human body was revealed by V. V. Petrov, the inventor of an electrochemical high-voltage source. The first written mentions of industrial electrical injuries date back only to 1863 - from constant exposure and 1882 - from variable exposure.

Electrical injuries and electrical injuries

Damage caused to the human body by the action of current, touch, step or exposure to an electric arc is usually called electrical injury. Depending on the specific conditions under which a person is exposed to electric current, its consequences may be different, but they have certain characteristic features:

- electrical influences the places of contact with live elements and metal parts to the human body, as well as directly on the path of current flow;

— the body’s reaction manifests itself only after exposure to current;

- electrical has a negative effect on the cardiovascular, nervous and respiratory system.

Electrical injuries among all types of industrial injuries have a relatively low percentage, however, in terms of the number of injuries with particularly severe and even fatal outcomes, it occupies one of the leading positions.

To reduce the likelihood of exposure to electric current, it is necessary to use appropriate equipment in accordance with safety precautions. Their use will allow you to safely perform work in electrical installations and avoid electrical injury.

Main types of electric shock

The effect of electric current on the body is complex and diverse. It has thermal, biological, electrolytic and mechanical effects.

1. Thermal effects manifest themselves in strong heating of tissues.

2. Biological - leads to disruption of the functioning of bioelectric processes, and is accompanied by irritation, excitation of living tissues, and strong muscle contraction.

3. Electrolytic effects result from the decomposition of many vital body fluids, including blood.

4. Mechanical impact causes ruptures and separation of living tissues, and a strong impact occurs due to intense evaporation of fluid from the organs and living tissues of the body.

Factors influencing the degree of action of electric current

The depth and nature of the effect of electric current are influenced by:

- current strength and its type (constant or alternating);

— current path and exposure time;

- features of the psychological, physiological state of a person in at the moment, as well as individual qualities and properties of the human body.

There are several threshold values ​​for the action of electric current:

1. Threshold perceptible - 0.6-1.5 mA on alternating and 5-7 mA on constant;

2. Threshold non-releasing (current that, when passing through the human body, causes convulsive muscle contractions) - 10-15 mA with alternating current, 50-80 mA with constant;

3. Threshold fibrillation (current that, when passing through the body, causes fibrillation of the heart muscle) - 100 mA - at alternating and 300 mA at constant.

As the amount of time the human body remains under voltage increases, the risk of serious injury and death increases. Also influenced by a person’s mass and the degree of his physical development. It has been proven that the threshold value of current exposure for women is 1.5 times less than under similar conditions for men.

The path of current flow also has a significant influence. The danger of damage increases many times when passing through vital organs and systems of the human body (lungs, heart muscle, brain).

We looked at it in a separate article. Their influence can also be attributed to the negative impact on humans.

Poster: First aid for electric shock.