Passing through the human body, an electric current causes:

1. thermal action;

2.electrolytic action;

3.biological action.

thermal action manifests itself in burns of individual parts of the body, heating of parts of the body.

Electrolytic action manifests itself in the decomposition of blood and other organic fluids.

Biological action It manifests itself as irritation and excitation of the living tissues of the body, which is accompanied by involuntary convulsive muscle contractions.

Electrical injury:

1.electrical burns;

2. electrical signs;

3.metallization of the skin;

4. electrophthalmia;

5.mechanical damage.

Electrical burn divided into current and arc. An arc burn occurs at a voltage of more than 1 kV and, as a rule, an arc temperature of more than 3.5 C. A current burn is caused by the passage of electric current through the human body as a result of contact with a live part and is a consequence of the conversion of electrical energy into heat.

electrical signs- clearly defined spots of gray or pale yellow color on the surface of the skin exposed to current. They come in the form of scratches, wounds, cuts. In most cases, they are painless.

Metallization of the skin - penetration into the upper layers of the skin of the smallest particles of metal. This can happen during short circuits and disconnection of circuit breakers under load.

Electrophthalmia- eye damage caused by intense radiation of the electric arc.

Mechanical damage arise as a result of sharp involuntary convulsive muscle contractions under the influence of an electric current. As a result, ruptures of the skin, blood vessels and nervous tissue can occur, as well as dislocations of the joints, even bone fractures. These injuries are serious injuries that require long-term treatment.

Factors that determine the risk of electric shock.

1. Electrical resistance of the human body.

2. The value of the potential difference in the electrical circuit.

3. Duration of exposure.

4. The path of current through the human body.

5. Rod and frequency of electric current.

6.Individual properties of a person.

7. Environmental conditions.

1. Electrical resistance of the human body.

The greatest resistance to electric current is provided by the skin, therefore the resistance of the human body is determined mainly by the resistance of the skin. The electrical resistance of the human body with dry, clean and intact skin, measured at 20 V, ranges from 3-100 kOhm, and the resistance of the inner layers is 300-500 Ohm. The electrical resistance of the human body is a complex quantity, it consists of active and capacitive, but, as a rule, capacitive is neglected. The skin of the face, neck, hands in the area above the palm has the least resistance, especially in the areas facing the torso. With an increase in exposure time, the resistance of the human body decreases, as this increases the local heating of the skin, which leads to vasodilation and an increase in the supply of blood to this area, and, accordingly, an increase in sweating.

Sensible current- an electric current that causes tangible irritations when passing through the body. For alternating current it is 0.6-1.5 mA, for direct current 5-7 mA.

Continuous current- an electric current that causes irresistible convulsive contractions when passing through the body. For alternating current it is 10-15 mA, for direct current 50-60 mA.

Fibrillation current is an electrical current that can cause asynchronous contractions of the heart muscle. The threshold current for AC is 100 mA, for DC it is 300 mA. With a duration of exposure of 1-2 seconds along the path of the arm - arm or arm - legs, the fibrillation current can reach 5 A. More than 5 A does not cause heart fibrillation - instant cardiac arrest occurs.

5. Type and frequency of electric current.

Direct current is approximately 4-5 times safer than alternating current. The significantly lower danger of direct current is confirmed by the practice of operating electrical installations. This provision is valid only for voltages of 250-300 V. But the greatest danger is alternating current with a frequency of 50-1000 Hz, with a further increase in frequency, the danger of damage decreases and completely disappears at a frequency of 45-50 kHz.

6. Individual properties of a person.

It has been established that physically healthy and strong people endure electric shocks more easily. Increased susceptibility to electric current have people suffering from diseases of the cardiovascular system, skin, organs of internal secretion.

7. Conditions of the external environment.

Dampness, conductive dust, caustic vapors and gases have a destructive effect on the insulation of electrical equipment. The impact of current on a person is also exacerbated by conductive floors and metal and grounded structures close to electrical equipment.

Premises according to the danger of electric shock are divided into:

1) premises without increased danger;

2) premises with increased danger, which are characterized by the presence of one of the following conditions:

Dampness or conductive dust;

conductive floors;

High room temperature (more than 35 C);

Possibility of simultaneous contact of a person with grounded metal structures on the one hand and metal cases of electrical equipment on the other.

3) especially dangerous premises - are characterized by the presence of one of the following conditions:

Particular dampness (relative humidity approx. 100%);

The presence of a chemically active or organic environment;

The presence of two or more high-risk conditions at the same time.

Electricity

According to modern concepts, electricity is a set of phenomena caused by the existence, movement and interaction of electrically charged bodies or particles (electrons, ions, molecules, their complexes, etc.), and electric current is an ordered and directed movement of electrons, ions. Accordingly, the electric current cannot be seen, but you can see, feel the results of converting electricity into other types of energy: light, heat, mechanical energy, etc., which can not only bring benefits, but also cause irreparable damage as a result of violation of the rules for using this type of energy. and in cases of emergency situations of natural and (or) man-made (anthropogenic) nature.

The physical parameters of the electric current are determined by the strength of the current, its frequency and type - AC or DC.

Factors that determine the outcome of electric shock

1. The magnitude of the current and voltage. Electric current as a damaging factor determines the degree of physiological impact on a person. Voltage should be considered only as a factor that determines the flow of a particular current under specific conditions - the greater the touch voltage, the greater the striking current.

According to the degree of physiological impact, the following damaging currents can be distinguished:

• 0.8-1.2 mA - threshold perceptible current (i.e., the smallest current value that a person begins to feel);
• 10-16 mA - threshold non-letting (chaining) current, when, due to convulsive contraction of the hands, a person cannot independently free himself from current-carrying parts; can cause electrical asphyxia - convulsive contraction of the respiratory muscles in the exhalation phase;
• 100 mA - causes ventricular fibrillation of the heart. In this case, it must be borne in mind that the probability of being struck by such a current is 50% with a duration of its impact of at least 0.5 s.

Alternating current from 100 mA to 5 A at a frequency of 50 Hz and direct current from 300 mA to 5 A act directly on the heart muscle, which is very life-threatening, because after one or two seconds from the moment the circuit of this current is closed, fibrillation can occur through a person - scattered, arrhythmic and uncoordinated contractions of individual groups of muscle fibers of the ventricles of the heart with a frequency of more than 300 contractions per minute. In this condition, the heart ceases to perform its pumping functions, and the blood supply to the entire body stops.

A current of more than 5 A, as a rule, does not cause cardiac fibrillation. With a further increase in the current strength, it acquires defibrillating properties, but causes a violation of the functions of the central nervous system and respiratory arrest of central origin.

• 2. Duration of current exposure. It has been established that electric shock is possible only in a state of complete rest of the human heart, when there is no compression (systole) or relaxation (diastole) of the ventricles of the heart and atria. Therefore, with a short time of current exposure, it may not coincide with the phase of complete relaxation, however, everything that increases the pace of the heart, increases the likelihood of cardiac arrest during an electric shock of any duration. Such reasons include: fatigue, agitation, hunger, thirst, fear, taking alcohol, drugs, certain drugs, smoking, illness, etc.
• 3. body resistance. The value is not constant, depends on specific conditions, varies from several hundred ohms to several megaohms. When exposed to a power frequency voltage of 50 Hz, the resistance of the human body is an active quantity, consisting of internal and external components. The internal resistance of all people is approximately the same and is 600-800 ohms. Different parts of the human body and tissues have different resistance to current: bones -
• 200,000 ohms; cartilage - 50,000 ohms; muscles - 1500 ohms; liver - 900 Ohm; mucous membranes - 100 ohms.

The skin has great resistance - 10,000-20,000 Ohm, especially thick and dry skin on the palms and soles - 2 MΩ.

From this we can conclude that the outcome of the injury, ceteris paribus, depends on the place of application of the current.

The resistance of the body is not a constant value: in conditions of high humidity it decreases 12 times, in water - 25 times, sharply reduces its acceptance of alcohol.

4. Current strength. The strength of the current is determined by the ratio of the voltage and resistance of the body through which it passes (/ = U/R).

Dry skin has a resistance of 0.1-2 MΩ, while wet skin has a resistance of 1 kΩ. Thus, a current of the same voltage, for example, 127 V, may in some conditions (dry skin) not cause serious damage (slight tingling), and in others (wet skin, damp floor) - lead to death from ventricular fibrillation. The current strength in the first case will be 1.27 mA, and in the second - 127 mA.

With an increase in voltage of more than 500 V, the value of skin resistance no longer matters, since a “breakdown” of the skin occurs at the contact point, current “marks” appear.

Alternating current with a frequency of 50 Hz, common in industry and in everyday life, is more dangerous than direct current of the same voltage. This provision applies to currents up to 500 V. At a given voltage, the danger of both types of current is equalized, and at voltages above 500 V, direct current is more dangerous than alternating current.

The path ("loop") of current through the human body. When investigating accidents associated with the impact of electric current, first of all it turns out which way the current flowed. The current at the entrance to the body branches, the main amount of electricity rushes in a straight line from the anode to the cathode. A person can touch current-carrying parts (or non-current-carrying metal parts that may be energized) with a variety of parts of the body. Hence the diversity possible ways current. The most likely routes are the following:

• "hand - hand" (40% of cases of defeat);
• "right arm - legs" (20%);
• "left arm - legs" (17%);
• "both arms - legs" (12%);
• "leg - leg" (6%);
• "head - legs" (5%).

All loops, except for the "leg - leg" loop, are called "large" or "full" loops, since the current captures the region of the heart. In these cases, 8-12% of the total current flows through the heart. The "leg - leg" loop is called "small", only 0.4% of the total current flows through the heart. This loop occurs when a person finds himself in the current spreading zone, falling under the step voltage.

Stepping is the voltage between two points of the earth, due to the spreading of current in the earth, while simultaneously touching them with the feet of a person. In this case, the wider the step, the more current flows through the legs. Such a current path does not pose a direct danger to life, however, under its influence, a person may fall and the current flow path will become life-threatening. For protection against step voltage serve as additional means of protection - dielectric boots, dielectric rugs. In the case when the use of these means is not possible, it is necessary to leave the spreading zone so that the distance between the feet standing on the ground is minimal - in short steps. It is also safe to move on a dry board and other dry, non-conductive objects.

The impact of current on the human body in terms of the nature and consequences of the lesion depends on the following factors:

• current values;
• duration of current exposure;
• frequency and type of current;
• applied voltage;
• resistance of the human body;
• paths for the passage of current through the human body;
• the state of human health;
• attention factor.

The outcome of electric shock as a whole is determined by the amount of energy “absorbed” by the body of the flow of electric current.
The amount of current flowing through the human body depends on the voltage, touch and resistance of the human body.

I H \u003d U PR / R H

The resistance of the human body is a non-linear value, depending on many factors: on the resistance of the skin (dry, wet, clean, damaged, etc.); on the magnitude of the current and the applied voltage; on the duration of current flow.

The upper horny layer of the skin has the greatest resistance:

• with the stratum corneum removed RF= 600-800 Ohm;
• for dry undamaged skin RF= 10-100 kOhm;
• with hydrated skin RF= 1000 Ohm.

According to the decision of the IEC (International Electrotechnical Commission), in calculations to ensure protection against electrical injuries, human resistance is taken equal to 1 kOhm, i.e. RF= 1000 Ohm.

With an increase in the current passing through a person, his resistance decreases, because. at the same time, the heating of the skin increases and sweating increases. For the same reason, the decrease RF with an increase in the duration of the current flow. The higher the applied voltage, the greater the current through the person and the faster the human skin resistance decreases.

It turns out that biological tissue responds to electrical stimulation only at the moment of increasing or decreasing current.

Direct current, as not changing in time in magnitude and voltage, is felt only at the moments of switching on and off from the source. Usually its effect is thermal (with prolonged use). At high voltages, it can cause electrolysis of tissue and blood. According to many researchers, direct current up to 450 V is less dangerous than alternating current of the same voltage.
Most researchers have come to the conclusion that alternating current of industrial frequency of 50-60 Hz is the most dangerous for the body.

This is explained as follows. When a direct current is applied to the cell, the particles of the intracellular substance are split into ions of different signs, which rush to the outer shell of the cell. If a cell is affected by a current of variable frequency, then, following the changes in the poles of the alternating current, the ions will move in one direction or the other. At a certain current frequency, the ions will have time to pass twice the width of the cell (back and forth). This frequency corresponds to the greatest perturbation of the cell and the violation of its biochemical functions (50-60 Hz).

With an increase in the frequency of the alternating current, the amplitude of the oscillations of the ions decreases, and in this case, there is a lesser violation of the biochemical functions of the cell. At a frequency of about 500 kHz, these changes no longer occur. Here, burns from the thermal effects of current are dangerous for humans.

It turns out that the current in the human body does not necessarily pass along the shortest path. The most dangerous is the passage of current through the respiratory organs and the heart along the longitudinal axis (from the head to the feet).

Part of the total current passing through the heart:

• path hand - hand - 3.3% of the total current;
• path left arm - legs - 3.7% of the total current;
• path right arm - legs - 6.7% of the total current;
• path leg - leg - 0.4% of the total current.

The outcome of the lesion when exposed to electric current depends on the mental and physical condition person.

With diseases of the heart, thyroid gland, etc. a person is subjected to a stronger defeat at lower current values, tk. in this case, the electrical resistance of the human body decreases and the overall resistance of the body to external stimuli decreases. It was noted, for example, that for women the threshold values ​​of currents are approximately 1.5 times lower than for men. This is due to the thinner skin of women.

When using alcoholic beverages, the resistance of the human body falls, the resistance of the human body and attention decrease. The outcome of the defeat is becoming more and more serious.

With collected attention, the resistance of the body increases and the likelihood of damage is somewhat reduced.

Impact on the body. Factors that determine the risk of electric shock

With the increase in the power supply of chemical enterprises, the number of people in contact with electrical equipment, instrumentation, lighting devices, etc. increases. Since almost all workers can contact enterprises with electrical installations operating at voltages up to 1000 V, the possibility of electric shock increases, especially if the electrical equipment is faulty or operated in violation of the "Electrical Installation Rules" (PUE).

In addition, the danger of electric shock differs from other industrial hazards (toxic substances, heated surfaces, noise, etc.) in that a person is not able to detect it remotely without special measuring instruments.

As for installations operating at voltages above 1000 V, then, as a rule, they are either fenced or people with special training work with them.

When passing through the human body, an electric current has the following types of effects:

1. thermal - burns, heating of blood vessels, nerves;
2. electrolytic - decomposition of blood and lymphatic fluid, t. a significant change in their physico-chemical properties;
3. biological - irritation and excitation of living tissues of the body, accompanied by involuntary convulsions of the muscles of the body, heart, lungs, which leads to disruption or complete cessation of the activity of individual organs, respiratory and circulatory systems.

These effects lead to two types of injury: electrical injury - clearly expressed local lesions of the body (burns, electrical signs, skin plating, mechanical damage, electrophthalmia) and electrical shock - electrical injury caused by the reflex action of an electric current, i.e. with. action on the central nervous system, as a result of which paralysis of the affected organs may occur.

Injury statistics show that of all registered cases of electric shock with loss of working capacity for more than 3 days, as well as fatalities, 19% are electrical injuries, 26% are electric shocks and 55% are mixed lesions.

Electric, or contact, burn - the result of the thermal effects of current at the point of contact with non-insulated current-carrying parts; it can be surface (typical for currents of industrial frequency up to 100 Hz) or internal (for currents with a frequency of tens and hundreds of kHz). The amount of heat released in human tissue, in this case, is determined by the Joule-Lenz law (in J)

Q=IchRcht, (8.1)

where Ich is the strength of the current passing through the human body. AND; Rh is the resistance of the human body. Ohm; t - current flow time, s.

There are four degrees of burns: I - reddening of the skin, II - the formation of blisters on the surface of the skin, III - charring of the skin, IV - charring of the subcutaneous tissue, muscles. Electrical burns should not be identified with thermal ones, for example, burns with an electric blast, the temperature in the channel of which can reach 4000 ° C (they are typical for installations with voltages above 1000 V).

Electric signs - clearly defined spots of gray or pale yellow color with a diameter of 1 mm; a specific lesion caused, according to many researchers, by the mechanical and chemical effects of current; arise upon contact with current-carrying parts, are painless and disappear with time.

Metallization of the skin - damage to the skin as a result of the penetration of the smallest particles of molten metal into it. Over time, the affected skin disappears, the area becomes normal and the pain disappears.

Mechanical damage is the result of sharp, involuntary, convulsive muscle contractions under the influence of current, as a result of which ruptures of the skin, blood vessels, nerves, and dislocations of the joints are possible.

An electric shock is observed with prolonged exposure to a small current (up to several hundred milliamps) and, as a rule, at a voltage of up to 1000 V. There are four degrees of shock: I - convulsive muscle contraction without loss of consciousness; II - the same, but with loss of consciousness; III - loss of consciousness, violation of cardiac activity and respiration; IV - clinical death, i.e. lack of blood circulation and respiration.

The severity of electrical injuries depends on a number of factors: the strength of the flowing current, the path of its passage, the magnitude and type of voltage, the electrical resistance of the human body, the duration of the current flow, as well as the health and individual characteristics of a person, the environment, etc.

The magnitude of the current flowing through the human body is the main factor on which the outcome of the lesion depends. The smallest value of the perceptible current, which depends on the type of current, the state of the person, the type of its inclusion in the circuit, is called the threshold perceptible current. For an industrial frequency of 50 Hz, its average value is 1 mA.

With an increase in current strength to 10 ... 15 mA, painful cramps occur in the muscles of the hands, so a person is not able to control their action and independently free himself from the conductor (electrode) clamped in his hand. The current value of 10 mA is called the threshold non-release current.

At a current strength of 25 ... 50 mA, a strong contraction of the respiratory muscles of the chest occurs, breathing becomes difficult or stops. The probability of damage to the respiratory system largely depends on the time of current flow through the body.

A further increase in the current to 100 mA can cause fibrillation of the ventricles of the heart, in which their chaotic contraction occurs and blood circulation is disturbed or completely stopped, i.e., clinical death occurs. The danger of fibrillation lies in the fact that the human heart cannot get out of this state on its own and restore its activity: urgent first aid is needed - artificial respiration and external (indirect) heart massage.

Otherwise, after 5 ... 6 minutes, the neurons of the cerebral cortex begin to die, and clinical death turns into biological. As a result, both here and abroad, a current of 100 mA is considered fatal.

The path of its passage in the human body (the "loop" of the current) has a significant impact on the outcome of an electric shock. 15 paths are described in the literature, however, the most probable current flow paths are as follows: arm - arm (up to 40%), right arm - legs (up to 20%), leg - leg. In this case, from 0.4 to 7% of the total current flows through the human heart.

Individual characteristics of the body - for example, health status, physical development, weight, readiness to work with electrical installations ("attention factor") - also affect the outcome of the lesion. It has been established that people with increased excitability, diseases of the cardiovascular system, internal secretion organs have increased sensitivity to the action of electric current.

The type and frequency of the current are essential in case of injury. It has been established that alternating current of industrial frequency 50 ... 60 Hz is 4 ... 5 times more dangerous than direct current. Currents with a frequency of 400...500 kHz ns do not irritate tissues and do not cause electric shock. However, these currents have a thermal effect.

A very significant influence on the magnitude of the current passing through the human body is exerted by the total electrical resistance of his body, which, with dry, intact skin, can vary over a very wide range: from 103 to 105 ohms, and sometimes more.

It is a non-linear value and depends on a number of factors: the condition of the skin (dry, moist, clean, damaged), the density and area of ​​contact with current-carrying parts, the strength of the passing current and the applied voltage, the time of current exposure.

The highest electrical resistance in the human body has the upper stratum corneum (epidermis) 0.05 ... 0.2 mm thick, consisting of dead cells filled with air. When the stratum corneum is removed, the resistance of the internal organs, vital for a person, does not exceed 800 ... 1000 Ohms. Therefore, when calculating the conditions of human electrical safety, its total electrical resistance Rch is taken equal to 1000 Ohm.

Knowing the electrical resistance of the human body and the interval of dangerous currents for it, it is possible to determine the interval of dangerous voltages. So, for the regulated values ​​of the threshold non-releasing current of 10 mA and Rch = 1000 Ohm, the safe voltage will be Uwithout = RchIch = 10 V.

The environment and the situation in the room can strengthen or weaken the effect of electric current, since they significantly affect the resistance of the human body, the insulation of current-carrying parts. In accordance with this, there is a certain classification of premises according to the danger of electric shock. Industrial and domestic premises are divided into three classes: 1 - without increased danger, 2-with increased danger; 3 - especially dangerous.

Premises without increased danger are dry (relative humidity does not exceed 60%) dust-free rooms with normal temperature and insulating floors (parquet, linoleum, etc.). These may include office premises, QCD premises, small laboratories, some warehouses for storing solid polymeric materials and finished products.

The premises with increased danger include: damp, in which the relative humidity of the air for a long time exceeds 75%, but does not reach 100%; hot, in which the air temperature for a long time exceeds 30 ° C; dusty, in which conductive process dust is released in an amount sufficient to penetrate under the casing of electrical equipment, settling on wires, which will create electrical circuit for the leakage of dangerous currents (dust can also be non-conductive); rooms with conductive floors - metal, earthen, reinforced concrete, brick, xylolite, etc. (eliminate transient resistance between man and earth); rooms in which simultaneous contact is possible, on the one hand, with earth-connected cases of technological equipment, metal structures of buildings, etc., and, on the other hand, with metal cases of electrical equipment or current-carrying parts. Such premises include areas of injection molding machines, warehouses for storage and areas for hanging ingredients with electrical conductivity (for example, hanging carbon black), etc.

Particularly dangerous premises include: especially damp premises, in which the relative humidity of the air is close to 100%, and in such premises the walls, floor, ceiling and objects located in them are covered with moisture: with a chemically active environment, where, according to production conditions, gases, vapors are contained or deposits are formed that destroy the insulation or live parts of electrical equipment; premises in which there are simultaneously two or more factors of increased danger.

Such premises include areas for the impregnation of polymeric materials, dry cleaning of molds, electroplating shops for plastic metallization, glue shops, showers, etc.

The danger of electric shock to a person is determined by factors of electrical (voltage, strength, type and frequency of current, electrical resistance of a person) and non-electrical nature (individual characteristics of a person, the duration of the current and its path through a person), as well as the state of the environment.
electrical factors. The strength of the current is the main factor determining the degree of damage to a person, and depending on this, the categories of impact are established: threshold perceptible current, threshold non-letting current and threshold fibrillation current.
The electric current of the smallest strength, which causes irritation to a person, is called a threshold perceptible current. A person begins to feel the effect of alternating current with a frequency of 50 Hz, with an average strength of about 1.1 mA, and direct current of about 6 mA. It is perceived as mild itching and slight tingling when alternating current or heating the skin at constant.
Threshold perceptible current, striking a person, can be an indirect cause of an accident, causing involuntary erroneous actions that aggravate the existing situation (work at height, near current-carrying, moving parts, etc.).
An increase in the superthreshold perceptible current causes muscle cramps and pain in a person. So, with an alternating current of 10-15 mA, and a constant 50-80 mA, a person is not able to overcome muscle cramps, unclench the hand that touches the current-carrying part, discard the wire and finds himself, as it were, chained to the current-carrying part. Such a current is called a threshold non-letting current.
The current exceeding it intensifies convulsive muscle contractions and pain sensations, spreading them to a large area of ​​the body. This makes breathing difficult for the chest, causing constriction of the blood vessels, which leads to an increase in blood pressure and an increase in the load on the heart. An alternating current of 80-100 mA, and a direct current of 300 mA directly affect the heart muscle, and after 1-3 seconds from the beginning of its exposure, cardiac fibrillation occurs. As a result, blood circulation stops and death occurs. This current is called the fibrillation current, and its smallest value is called the threshold fibrillation current. An alternating current of 100 mA or more instantly causes death from cardiac paralysis. The greater the value of the current passing through a person, the greater the danger of injury, but this dependence is ambiguous, since the danger of injury also depends on a number of other factors, including non-electric ones.
Type and frequency of current. At voltages up to 250-300 V, direct and alternating currents of the same strength have different effects on a person. This difference disappears at higher voltages.
The most unfavorable is alternating current with an industrial frequency of 20-100 Hz. With an increase or decrease beyond these limits, the values ​​of the non-letting current increase, and at a frequency equal to zero (direct current), they become approximately 3 times larger.
Human circuit resistance to electric current. The electrical resistance of a human circuit (Rch) is equivalent to the total resistance of several elements connected in series: the human body r incl., clothing r od (when touched by a body area protected by clothing), shoes r about and the supporting surface

R h \u003d r incl. +r od +r rev +r op

From equality, we can conclude: the insulating ability of floors and shoes is of great importance to ensure the safety of people from electric shock.
Individual resistance ability of the human body. The electrical resistance of the human body is an integral part when it is included in an electrical circuit. The skin has the greatest electrical resistance, and especially its upper stratum corneum, which is devoid of blood vessels. The resistance of the skin depends on its condition, the density and area of ​​contacts, the magnitude of the applied voltage, the strength and time of the current. Clean, dry, intact skin provides the greatest resistance. An increase in the area and density of contacts with live parts reduces its resistance. As the applied voltage increases, the skin resistance decreases as a result of breakdown of the upper layer. Increasing the current strength or the time of its flow also reduces the electrical resistance of the skin due to heating of its upper layer.
The resistance of the internal organs of a person is also a variable, depending on physiological factors, health, mental state. In this regard, persons who have undergone a special medical examination and do not have skin diseases, diseases of the cardiovascular, central and peripheral nervous systems and other diseases are allowed to service electrical installations. When carrying out various calculations but ensuring electrical safety, the resistance of the human body is conventionally assumed to be 1000 ohms.
The duration of the current. An increase in the duration of current exposure to a person aggravates the severity of the lesion due to a decrease in body resistance due to moisturizing the skin with sweat and a corresponding increase in the current passing through it, depleting the body's defenses that resist the effects of electric current. There is a certain relationship between the permissible values ​​of contact voltage and current strength for a person, the observance of which ensures electrical safety. Touch voltage is the voltage between two points in a current circuit that are simultaneously touched by a person.
The maximum allowable levels of contact voltage and current strength above the releasing ones are set for current paths from one hand to the other and from hand to foot, GOST 12.1.038-82 “SSBT. Electrical safety. Maximum permissible levels of touch voltages”, which for normal (non-emergency) operation of electrical installations with a duration of exposure of not more than 10 minutes per day should not exceed the following values: with alternating (50 Hz) and direct current (respectively, voltage 2 and 8 V, current strength respectively 0.3 MA).
When working at food enterprises in conditions of high temperatures (> 250C) and relative air humidity (> 75%), the indicated values ​​​​of contact voltage and currents must be reduced by 3 times. In emergency mode, i.e., during operation of a faulty electrical installation that threatens electrical injury, their values ​​\u200b\u200bare indicated in Table. four.
From the data in Table. 4 it follows that with an alternating current with a power of C mA and a constant 15 mA, a person can independently free himself from current-carrying parts for a period of more than 1 s. These currents are considered to be continuously admissible if there are no circumstances exacerbating the danger.
Table 4

	Standardized value	Maximum permissible levels, no more, with prolonged exposure to current
Variable (50 Hz)
Constant

The current path through a person significantly affects the outcome of the lesion, the danger of which is especially great if it passes through vital organs: the heart, lungs, and brain.
In the human body, the current does not pass through the shortest distance between the electrodes, but moves mainly along the flows of tissue fluid, blood and lymphatic vessels and the membranes of the nerve trunks, which have the highest electrical conductivity.
Current paths in the human body are called current loops. For electrical injuries with a severe or fatal outcome, the following current loops are most characteristic: arm-arm (40% of cases), right arm-legs (20%), left arm-legs (17%), leg-leg (8%).
Many environmental factors in the production environment significantly affect electrical safety. In humid rooms with high temperatures, the conditions for ensuring electrical safety are unfavorable, since in this case the thermoregulation of the human body is carried out mainly with the help of sweating, and this leads to a decrease in the resistance of the human body. Grounded metal conductive structures increase the risk of electric shock due to the fact that a person is almost constantly connected to one of the poles (ground) of an electrical installation. Conductive dust increases the possibility of accidental human contact with live parts and earth.
Depending on the influence of the environment, the "Electrical Installation Rules" (PUE) classify industrial premises according to the degree of danger of electric shock to a person.
Premises with increased danger, characterized by the presence in them of one of the following signs:

• dampness (relative air humidity exceeds 75% for a long time);
• conductive dust that can settle on wires, penetrate into machines, devices, etc.;
• conductive floors (metal, earthen, reinforced concrete, brick, etc.);
• high air temperature (constantly or periodically exceeding 35 ° C, for example, rooms with dryers, boiler rooms, etc.);
• the possibility of a person simultaneously touching the metal structures of buildings connected to the ground, technological devices, mechanisms, etc., on the one hand, and to the metal cases of electrical equipment, on the other. An example of premises with increased danger can be in brewing and non-alcoholic production - fermentation department, departments for the preparation of dry drinks, shops for finished products; drying and elevator departments of starch and syrup production; dough preparation departments of bakeries.

Particularly dangerous premises, characterized by the presence of one of the following features:

• special dampness (relative air humidity is close to 100%, the ceiling, walls, floor and objects in the room are covered with moisture);
• chemically active or organic environment (aggressive vapors, gases, liquids that form deposits or mold that destroy insulation and current-carrying parts of electrical equipment);
• two or more signs of high-risk premises at the same time. The premises of this class, for example, include bottle-washing departments, blend bottling shops, syrup brewing at beer and non-alcoholic industries; syrup, cooking, separator departments of starch and syrup production.

Premises without increased danger are those in which there are no signs of the above premises.
Territories of location of outdoor electrical installations are equated to especially dangerous premises.

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