Impact electric current on the human body is unique and versatile. Passing through the human body, the electric current produces thermal, electrolytic, mechanical and biological effects.

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

It's not voltage that kills, it's current.

This is perhaps the most basic problem of the vast majority ordinary people. Everyone thinks tension is dangerous, but they are only partly right. By itself, the voltage (potential difference between two points of the circuit) does not affect the human body in any way. All processes related to the lesion take place under the influence of an electric current of one size or another.

Higher current - more danger. Partially correct about voltage is that the current strength depends on its value. That's right - no more, no less. Everyone who went to school will easily remember Ohm's law:

Current = voltage / resistance (I=U/R)

If we consider the resistance of the human body as a constant value (this is not entirely true, but more on that later), then the current, and hence the damaging effect of electricity, will directly depend on the voltage. Higher voltage - higher current. This is where the belief comes from that the higher the voltage, the more dangerous it is.

Connection of current with resistance

According to Ohm's law, current also depends on resistance. The lower the resistance, the higher and, therefore, the more dangerous the current. There will be no conditions for the passage of current (circuit resistance is infinite) - there will be no danger at any voltage

Suppose (only theoretically) you stick your finger into the socket while standing on damp ground and get a powerful blow. Since your body has low resistance, the current from the outlet will rush through the human-to-ground circuit.

And now, before you put your finger in the socket, you stood on a dielectric mat or put on dielectric boots. The resistance of a dielectric mat or bot is so high that the current through them and, accordingly, you, will be negligible - microamps. And although you will be under a voltage of 220 V, there will be practically no current flowing through you, which means that you will not receive an electric shock. You won't feel any discomfort at all.

It is for this reason that a bird sitting on a high-voltage wire (it is bare, do not hesitate) calmly cleans its feathers. Moreover, if an overly jumpy person, a kind of Batman, jumps up and grabs the phase wire of a power line, nothing will happen to him either, although he will be energized in kilovolts. Hang and jump. Electricians even have this type of work - energized (do not confuse with work on electrical installations that are energized).

But back to the version with the socket, in which you stood on damp ground. Hit is a fact. But how strong?

Determination of the degree of damage

The resistance of the human body under normal conditions is 500-800 ohms. The damp earth resistance can be ignored - it can turn out to be extremely low and not affect the result of the calculations, but in fairness let's add another 200 ohms to the body resistance. Quickly calculate with the above formula:

220 / 1000 = 0.22 A or 220 mA

The degree of action of current on the human body Briefly, it can be expressed through the following list:

• 1-5 mA - tingling sensation, slight cramps.
• 10-15 mA - severe muscle pain, convulsive contraction. It is possible to free yourself from the action of the current.
• 20-25 mA - severe pain, muscle paralysis. It is almost impossible to get rid of the action of the current on your own.
• 50-80 mA - respiratory paralysis.
• 90-100 mA - cardiac arrest (fibrillation), death.

Obviously, a current of 220 mA far exceeds the lethal value. Many will say that the resistance of the human body is much more than a kilo-ohm. Right. The resistance of the upper layer of the skin (epidermis) can reach a megaohm or even more, but this layer is so thin that it immediately breaks through with a voltage above 50 V. Therefore, in the case of electrical outlets, you can not count on your epidermis.

The danger depends on the frequency

At voltages up to 400 V, alternating current with a frequency of 50 Hz is much more dangerous than direct current, since, firstly, the resistance of the human body to alternating current is lower than direct current. Secondly, the biological effect of an alternating type electric current is much higher than that of a direct one.

At high voltages, and, as a result, high direct currents, the electrolysis process that occurs in cellular fluids is added to the list of damaging factors. In this case, direct current becomes more dangerous than alternating current. It simply changes the chemical composition of body fluids. As the frequency increases, the picture changes somewhat: the current begins to have a surface character.

In other words, it passes over the surface of the body without penetrating deep into the body. The higher the frequency, the smaller the "layer" human body suffers. For example, at a frequency of 20-40 kHz, heart fibrillation does not occur, since no current flows through it. Instead of this misfortune, another one appears - at a high frequency, a severe lesion (burn) of the upper layers of the body occurs, which, with no less success, leads to death.

Electrical pathways through the body

The effect of current on the human body depends not only on its magnitude, but also on the path of passage. If a person simply climbed into the socket with his fingers, then the current will flow only through the brush. He stands on the damp floor and touched the bare wire - through his arm, torso and legs.

It is quite obvious that in the first case only the hand will suffer, and it will not be difficult to get rid of the action of the electric current, since the muscles of the arm above the hand will retain controllability. The second case is much more serious, especially if the hand is left. Here, the current fetters the muscles, preventing a person from freeing himself from the action of electricity. But worst of all, in this case, the lungs, heart and other vital organs suffer. The same problems await on the way hand-hand, head-hand, head-legs.

The effect of electric current on a person

passing through the human body, electricity has several types of effects on the body at once. Total there are four of them:

1. Thermal (heating).
2. Electrolytic (dissociation leading to disruption chemical properties liquids).
3. Mechanical (tissue rupture as a result of hydrodynamic impact and convulsive muscle contraction).
4. Biological (violation of biological processes in cells).

Depending on the magnitude, path of passage, frequency and duration of exposure, electric current can cause absolutely different damage to the body, both in nature and severity. . The most common of them can be considered:

1. Convulsive muscle contraction.
2. Convulsive muscle contraction, breathing and heartbeat persist.
3. Respiratory arrest, possible cardiac arrhythmias.
4. Clinical death, no breathing or heartbeat.

Safe Voltage

To clarify this issue, you do not need to use any formulas - everything has already been calculated, recorded and endorsed by specially trained people. Depending on the type of current according to PES It is recommended to consider as a safe voltage:

Variable up to 25 V or constant up to 60 V - in rooms without increased danger;

AC up to 6 V or DC up to 14 V - in high-risk rooms (damp, metal floors, conductive dust, etc.).

Definition of step voltage

This question, which is of purely academic interest, requires an answer, if only because almost anyone who leaves the house can get under the stress of a step. So, suppose a wire breaks on a power line and falls to the ground. In this case, no short circuit occurred (the earth is relatively dry and the emergency protection device did not work). But even dry ground has a fairly low resistance and current flows through it. Moreover, it flowed in all directions, both in depth and on the surface.

Due to the resistance of the soil, when moving away from the wire, the voltage gradually drops and disappears at some distance. But in fact, it does not disappear without a trace, but is evenly distributed, "smeared" on the ground. If you stick the voltmeter probes into the ground at a certain distance from each other, the device will show a voltage that will be the higher, the closer the fallen wire and the greater the distance between the probes.

If instead of probes there are legs of a person briskly going to work, then he will fall under voltage, which is called stepping. The closer the dropped wire and the wider the pitch, the higher the voltage.

This type of tension threatens with the same thing as the usual one - with a defeat of one degree or another. Even if the current flowing through the leg-leg loop turns out to be not particularly dangerous, it may well cause convulsive muscle contraction. The victim falls and falls under a higher voltage (the distance of the arm - the leg is greater), which, moreover, begins to flow through the vital organs. Now there can be no talk of safety - a person has come under life-threatening stress.

If you feel that you have fallen under the voltage of a step (the sensation can be compared with those that arise from touching an “electric-fighting” washing machine). Put your feet together, minimizing the distance between them, and look around. If you see an electrical pole (pole) or a transformer substation within a radius of 10-20 m, then, most likely, the ears of the problem grow from there. Start moving in the opposite direction from them in steps of a few centimeters. Do you remember what less step, the lower the step voltage. If it is impossible to understand where the tension came from, choose an arbitrary direction.

5.7.1. Impact of electric current

Passing through the human body, the current has a thermal, electrolytic, mechanical and biological effect.

thermal effect manifested by burns of certain parts of the body, heating of blood vessels, nerves and other tissues, causing significant functional disorders. electrolytic effect It is expressed in the decomposition of biological fluids, including blood, as a result of which their physical and chemical composition is disturbed. Mechanical impact leads to stratification, rupture of body tissues as a result of the electrodynamic effect, as well as the explosive formation of steam, which is formed when biological fluids boil under the influence of current. Biological impact manifested by irritation and excitation of body tissues, violation of vital biological processes, resulting in possible cardiac arrest and cessation of breathing. An external current can suppress very small biocurrents flowing in the human body, and thereby cause serious disorders in the body until death.

The considered effects of current on the body often lead to electrical injury, which are subdivided into general(electric shocks) and local, moreover, they often occur simultaneously, forming mixed electrocution.

Under electric shock understand the excitation of body tissues by the current passing through it, manifested in the form of muscle spasms of the body. The severity of the consequences of such exposure is different: from weak muscle contraction at the points of current entry and exit to significant disorders, including the cessation of the functioning of the heart and lungs. Even with a non-fatal electrical injury, the electrocardiogram of the victim bears signs of coronary insufficiency, and morphological studies in some cases show the presence of myocardial infarction. Often, the victims have long-term (from 10 days to 2 years or more after the injury) consequences of electric shocks: diseases thyroid gland, genital organs, early appearance of arteriosclerosis, development of diabetes, cardiovascular, vegetative-endocrine and neuropsychiatric disorders.

To local electrical injuries include electrical burns, skin plating, electrical signs, mechanical damage and electrophthalmia.

electrical burns occur in about two-thirds of the victims due to the conversion into thermal energy of the electrical energy of the current passing through the human body when it comes into contact with live parts, as well as from the impact of an electric arc or spark generated during short circuits or a person approaching an unacceptably close distance to the parts located under high voltage.

Leather plating is associated with the penetration of the smallest particles of metal into it during its melting and splashing in the event of an electric arc. Metal can also penetrate the skin as a result of electrolysis at the points of contact of a person with current-carrying parts. This injury is observed in approximately one in ten victims. Over time, the affected area of ​​the skin acquires normal view and elasticity. However, if the eyes are affected, treatment can be difficult, sometimes ineffective - blindness occurs.

electrical signs- these are patches of gray or pale - yellow color formed on the skin during the passage of current. There is a kind of necrosis of the upper layer of the affected area of ​​the skin and its hardening like a callus. Usually, electrical signs are painless and disappear without a trace during treatment. This type of injury occurs in approximately 11–20% of victims.

Mechanical damage tissues and organs of the human body are observed quite rarely and occur as a result of convulsive muscle contractions under the influence of current. The consequences of injury are sometimes very severe: ruptures of tendons, blood vessels, dislocations of joints and fractures of bones.

Electrophthalmia(inflammation of the outer membranes of the eyes) occurs as a result of exposure to ultraviolet radiation electric arc. Characteristic manifestations diseases: lacrimation, partial blindness and photophobia; eye pain usually lasts for several days.

As a result of statistical processing of numerous and very different data obtained from the analysis of accidents, the results of experiments on animals and humans, an average dependence of the nature of the impact on the value of direct and alternating current passing through a person along the path "hand-hand" and "hand -legs "(Table 7).

Table 7

The impact of current on a person

What is electrical injury and electrical injury?

Electrical injury - damage to the human body by electric current (electric arc).

The phenomenon of electrical injury is explained by the sequence of the following features: in the body of a person who accidentally finds himself under the influence of stress, a protective reaction occurs. In other words, resistance to electric current begins to occur at the moment of its direct flow through our body. In such situations, there is not only a strong effect of currents on the human body, but also a violation of blood circulation, respiration, cardiovascular and nervous system etc.

electrical injuryit is not easy to predict, since it is obtained not only by direct contact with current-carrying elements, but also by interaction with an electric arc and step voltage.

Electrical injury although it happens less often than other types of industrial injuries, it is in the first places among those injuries that are assessed as severe and fatal. The largest percentage of injuries caused by the influence of electric current occurs while working on high voltage electrical installations (up to 1000 V). main reason electrical injury is the frequent use of just such types of electrical installations, as well as insufficient qualifications of workers. Of course, there are units with more high rate voltage (over 1000 V), but, oddly enough, electric shocks are rare in their operation. This pattern is explained by the high professionalism and competence of the personnel serving high-voltage installations.

The most common causes of electric shock are:

• direct bodily contact with non-insulated live parts;
• touching parts of electrical equipment made of metal;
• touching non-metallic elements under strong voltage;
• interaction with step voltage current or with an electric arc.

Impact of electric current when passing through the human bodythermal, electrolytic and biological.

• Thermal exposure - strong heating of tissues, which is often accompanied by burns.
• Electrolytic action is the decomposition of organic fluids, which include blood.
• Biological impact - violation of bioelectric processes, irritation and excitation of living tissues, frequent and erratic muscle contraction.

Electric shocks are divided into two main types:

• electrical injury - local lesions of tissues or organs (burns, signs, electroplating).
• An electric burn is the result of a strong current heating (over one ampere) of human tissues. Burn that strikes only skin covering, is called surface; damaging the deep tissues of the body is internal. Also, electrical burns are divided according to the principle of occurrence: contact, arc, mixed.
• An electric sign looks like a gray or pale yellow spot resembling a corn. This injury occurs in the area of ​​\u200b\u200bcontact with a current-carrying element. Basically, signs are not followed severe pain and after a short amount of time they leave.
• Electroplating is a phenomenon in which human skin is impregnated with metal microparticles. This happens at the moment when the metal under the influence of current evaporates and splashes. Affected skin acquires a color corresponding to the penetrating metal compounds and becomes rough. The process of electroplating is not dangerous, and the effect after it disappears after some time, similar to electric signs. Metallization of the organs of vision has much more serious consequences.

In addition to burns, signs and electroplating, electrical injuries also includeelectrophthalmia and various mechanical damage. The latter are the result of involuntary muscle contractions at the time of current flow. These include severe ruptures of the skin, blood vessels, nerves, as well as dislocations and fractures.Electrophthalmia- a phenomenon that is a strong inflammation eyeballs after exposure to UV rays of an electric arc.

• electric shock expressed in the form of a strong excitation of living tissues after exposure to an electric current. As a rule, this phenomenon is accompanied by erratic convulsive muscle contraction. The outcome of electric shocks is different, on the basis of which they are divided into five kinds:
• without loss of consciousness;
• with loss of consciousness, accompanied by a violation of the functioning of the heart and breathing;
• with loss of consciousness, but no malfunction of cardio-vascular system and without respiratory failure;
• clinical death;
• electric shock.

The last two types are worth considering in more detail.

clinical death otherwise also called "imaginary" death, characterized by a duration of 6-8 minutes. This phenomenon is considered a transitional state from life to death, which is accompanied by the cessation of the heart and the suspension of breathing. After the above period of time, an irreversible process of death of the cells of the cerebral cortex begins, which ends with biological death.

You can recognize imaginary death by the following signs:

• fibrillation of the heart (i.e., a disparate contraction of its muscle fibers, accompanied by a violation of synchronous activity and pumping function) or its complete stop;
• lack of pulse and breathing;
• bluish skin color;
• dilated pupils without responding to light, as a result of a lack of oxygen in the cerebral cortex.

electric shock is a severe neuroreflex reaction of the human body to the effects of current. This phenomenon is accompanied by severe respiratory disorders, the functioning of the circulatory and nervous systems, etc.

The body instantly reacts to the influence of an electric current, entering a phase of strong excitation. During this period, there is a complete reaction to the infliction of pain, accompanied by an increase blood pressure and other processes. The excitation phase is replaced by a phase of inhibition, which is characterized by exhaustion of the nervous system, weak breathing, alternating drop and increase in heart rate, and a decrease in blood pressure. All listed signs lead aboutbody in a state deep depression. An electric shock can last for several tens of minutes or several days. The result can be polar opposite: either full recovery or irreversible biological death.

The effect on the human body directly depends on the current strength indicator:

• 0.6-1.5 mA at AC (50Hz) and 5-7 mA at DC - perceptible current;
• 10-15 mA at alternating current (50 Hz) and 50-80 mA at direct current - not letting go of the current, which, at the moment of passing through the body, provokes strong convulsive contractions of the muscles of the hand that compresses the conductor;
• 100 mA at AC (50Hz) and 300 mA at DC is a fibrillation current that leads to cardiac fibrillation.

The result of the influence of electric current on the human body also directly depends on the following factors:

• current flow duration. That is, than longer man was under the influence, the higher the danger and the more serious the injuries;
• specific features every organism at the moment : body weight, physical development, the state of the nervous system, the presence of any diseases, alcohol or drug intoxication, etc .;
• "attention factor", i.e. preparedness for the possibility of receiving an electric shock;
• current path through human body. For example, a more serious danger is the passage of current through the heart, lungs, brain. If the current bypasses the vital organs, the risk of serious injury is sharply reduced. To date, the most popular path for the passage of current has been fixed, which is called the "current loop" - the right arm-legs. The loops taken away from a person's working capacity for more than three days are the hand-hand (40%), right hand-foot (20%), left hand-foot (17%) paths.

Knowledge of the effect of electric current on the human body is essential. This will help you in emergency situations provide the right to the victim.

Commercial network "Planet Electric"has a wide range various means protection during various works, which can be found in more detail

The damaging effect of electric current on the human body is commonly called electrical injury. It should be taken into account that this type of industrial injuries is characterized by a large number of outcomes with severe and even fatal consequences. Below is a graph showing the percentages between them.

As statistics show, the largest percentage of electrical injuries (from 60 to 70%) falls on the operation of electrical equipment up to 1000 volts. This indicator is explained both by the prevalence of installations of this class and by the poor training of working personnel.

In most cases, electrical injury is associated with a violation of safety standards and ignorance of the elementary laws of electrical engineering. For example, electrical safety does not allow the use of foam fire extinguishers as the primary means of extinguishing electrical equipment.

Occupational safety requires that everyone who works on electrical equipment must without fail were trained in electrical safety. Where it is told about the danger of electric current, what measures should be taken in case of electrical injuries, as well as ways to provide the necessary assistance in these cases.

Note that the number of electrical injuries is significantly lower among those servicing electrical equipment with voltages above 1000V, which indicates a good training of such specialists.

Factors affecting the outcome of electric shock

There are several dominant reasons on which the nature of damage during electric shock depends:

Types of impact

An electric current with a strength of 0.5 to 1.5 mA is considered the minimum for human perception, when this threshold value is exceeded, a feeling of discomfort begins to appear, which is expressed in an involuntary contraction muscle tissue.

At 15 mA or more, control over muscular system. In this state, it is not possible to break away from the electric source without outside help, therefore this threshold value of the electric current strength is called unreleased.

When the strength of the electric current, passing the line of 25 mA, there is a paralysis of the muscles responsible for the work respiratory system which threatens to suffocate. If this threshold is significantly exceeded, fibrillation (failure of the heart rhythm) occurs.

Video: the effect of electric current on the human body

Below is a table that shows the allowable voltage, current and time of their exposure.

Electrical shocks can produce the following types impacts:

• thermal, burns appear varying degrees, which can disrupt the functioning of both blood vessels and internal organs. Let us note that the thermal manifestation of the action of an electric current is observed in most electrical injuries;
• the effect of an electrolytic nature causes a change in the physical and chemical composition tissues, due to the breakdown of blood and other body fluids;
• physiological, leads to convulsive contractions of muscle tissue. Note that the biological effect of the electric current also disrupts the work of other important organs, such as the heart and lungs.

Types of electrical injuries

The impact of electric current causes the following characteristic damage:

• electrical burns may occur due to the passage of an electric current or be caused by an electric arc. Note that such electrical injuries are most common (about 60%);
• the appearance on the skin of oval spots of gray or yellow color in places where the electric current passes. The dead layer of the skin becomes coarse, after some time such a formation, called an electric sign, disappears on its own;
• the penetration of small particles of metal (melted from short circuit or electric arc) into the skin. This type of injury is called skin plating. The affected areas are characterized by a dark metallic shade, touching it causes pain;
• light action, causes electrophthalmia ( inflammatory process eye shell) due to the ultraviolet radiation characteristic of the electric arc. For protection, it is enough to use special glasses or a mask;
• mechanical impact (electric shock) occurs due to involuntary contraction of muscle tissue, as a result of this, a rupture of the skin or other organs may occur.

Note that of all the electrical injuries described above, the consequences of an electric shock are the most dangerous, they are divided according to the degree of impact:

1. cause contractions of muscle tissue, while the victim does not lose consciousness;
2. convulsive contractions of muscle tissue, accompanied by loss of consciousness, the circulatory and respiratory systems continue to function;
3. there is paralysis of the respiratory system and a violation of the heart rhythm;
4. the onset of clinical death (no breathing, heart stops).

Step voltage

Given the frequent cases of damage from step voltage, it makes sense to tell more about the mechanism of its action. A break in a power line, or a violation of the integrity of the insulation in a cable laid underground, leads to the formation of a dangerous zone around the conductor, in which the current "spreads".

If you enter this zone, you can be exposed to the step voltage, its value depends on the potential difference between the places where a person touches the ground. The figure clearly shows how this happens.

The figure shows:

• 1 - electrical wiring;
• 2 - the place where the broken wire fell;
• 3 - a person who has fallen into the zone of electric current spreading;
• U 1 and U 2 are the potentials at the points where the feet touch the ground.

The step voltage (V W) is determined by the following expression: U 1 -U 2 (V).

As can be seen from the formula, the greater the distance between the feet, the greater the potential difference and the higher Vsh. That is, when you get to the area where the "spreading" of the electric current occurs, you can not take big steps to get out of it.

How to act when assisting with electrical injuries

First aid for electric shock consists in a certain sequence of actions:

The effect of electric current on the human body

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

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

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

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

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

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

1. parameters of the electric current flowing through the human body (voltage, frequency, type of current applied to the body),
2. current paths through the human body (arm-arm, arm-leg, leg-leg, neck-legs, etc.),
3. the duration of the effect of current through the human body,
4. conditions external environment(humidity and temperature),
5. the state of the human body (thickness and moisture content of the skin, health status and age).

dangerous and harmful effect electric current on people manifests itself in the form electric shocks and electric shocks.

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

Depending on the magnitude of the electric current and the time of its exposure, a person may be conscious or unconscious, but this ensures normal work heart and breath. In more severe cases, loss of consciousness is accompanied by disruption of the human cardiovascular system and even leads to lethal outcome. Electrical shock can cause paralysis the most important organs human body (heart, lungs, brain, etc.).

electrical injury called such an action of electric current on the human body, in which tissues and internal organs of a person (skin, muscles, bones, etc.) are damaged.

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

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

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

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

Respiratory arrest due to muscle paralysis chest may be the result of either the direct passage of an electric current through the chest area or reflexively, due to paralysis of the nervous system.

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

Prolonged shock may result in death. If in time to provide the victim medical care, then state of shock can be removed without consequences for a person.

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

The horny upper layer of human skin does not have blood vessels and has a very high resistivity - about 10 8 Ohm×cm. The inner layers of the skin, saturated with blood vessels, glands and nerve endings, have little specific resistance.

It is conditionally possible to consider the human body as a part electrical circuit, consisting of 3 sequentially connected sections: skin - internal organs - skin.

The circuit diagram of human substitution is shown in fig. 1.1.

Fig. 1.1 Schematic diagram of human substitution, where: G to- skin resistance; C to- capacitance between the electrode and the inside of the body; H ext- resistance of internal organs

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

The resistance of the human body (R h) is a variable value depending on the condition of the human skin (thickness of the horny cut of the skin, humidity) and environment(humidity and temperature).

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

In electrical calculations, the value of 1000 ohms is taken as the calculated value of the resistance of the human body.

The magnitude of the current and voltage

The main factor affecting the outcome of an electric shock to a person is the magnitude of the current, which, according to Ohm's law, depends on the magnitude of the applied voltage and the resistance of the human body. This dependence is not linear, since at voltages of about 100 V and above, a breakdown of the upper stratum corneum of the skin occurs, as a result of which the electrical resistance of a person sharply decreases (becomes equal to r ext), and the current increases. The voltage applied to the human body also affects the outcome of the lesion, but only in so far as it determines the value of the current passing through the person.

Type and frequency of electric current

The impact on a person of direct and alternating current is different - alternating current of industrial frequency is more dangerous than direct current of the same value. Cases of damage in electrical installations with direct current are several times less than in similar installations with alternating current at more high voltages(more than 300 V) direct current is more dangerous than alternating current (due to intensive electrolysis).

With an increase in the frequency of the alternating current, the impedance of the body decreases, which leads to an increase in the current through the person, and therefore, the risk of injury increases. The greatest danger is the current with a frequency of 50 to 1000 Hz; with a further increase in frequency, the danger of damage decreases and completely disappears at a frequency of 45-50 kHz. These currents maintain a risk of burns. The decrease in the risk of electric shock with increasing frequency becomes practically noticeable at 1-2 kHz.