Being under the influence of electrical voltage, the human body behaves exactly like an electrical conductor, since it contains a large volume of fluid (about 80% of the total body weight). Any liquid (intracellular, in the blood, in muscles, skin) is an electrolyte that conducts electricity well.
Based on this, under the action of the applied potential, the body conducts a current that affects a living organism and can cause irreversible changes in it, which end in injury or death.
Current action
Moving through the human body, charge carriers cause different kinds impacts depending on time, conditions and magnitude:
- Physiological (biological) impact of current. The most sensitive effect of electric current on the human body, and it is observed almost always. It is expressed in spontaneous spasms of muscle fibers, acting directly on the muscles or causing their response through the nervous system;
- Thermal effect of current. It manifests itself as burn damage to the skin and deeper tissues, since it has the same principle as the heating of conductors;
- Electrolytic effect of electric current on the human body. It is among the most dangerous. Liquid media are electrolytes. These include blood plasma, the fluid inside cells. Under the influence of current, liquids are subject to electrolysis, causing irreversible changes.
With any type of action of electric current on the human body, electrical injuries of various origins and degrees of consequences occur:
- Burns are the most significant part of electrical injuries as a result of the impact of electric current on the body. According to the degree of damage, superficial and internal burns are distinguished. Due to the occurrence, there are contact, which occur with direct exposure, arc - due to a discharge that has arisen nearby, and mixed. The thermal effect is especially pronounced at high current strength (above 1 A). With this value, a person is able to survive only with a very short pulse duration;
- Electrical signs. Where the place of the electric shock was concentrated, gray or pale yellow marks can be observed on the surface of the skin;
- Leather metallization. As a result of the spraying of metal particles from the current-carrying parts, its particles are introduced into the skin. The outer surface of the skin in these places acquires a metallic hue and is very painful;
- mechanical injury. Are the result of severe muscle cramps and, as a result, muscle tissue and tendons get ruptured;
- Electrophthalmia. It is damage to the mucous membrane of the eyes from the action of the ultraviolet component of the spectrum of an electric arc discharge. It is not actually an electrical injury, but often accompanies electrical discharges due to a short circuit.
Dangerous values
Electric current of different sizes affects the body in different ways. According to averaged data, a person begins to feel the effect of voltage, starting from a small value, about 0.6-1.0 mA for AC and 5-7 mA for DC. Strong and irresistible muscle spasms (non-release current) begin with a value of 10 mA. An increase to 50 mA provokes paralysis of the respiratory system. At a current of 100 mA, cardiac fibrillation begins.
The danger from the action of electric current on the human body depends not only on its parameters, but also on time. The body of most people is able to withstand short-term current pulses much greater than the above values.
Why is the value of current taken into account when determining the degree of danger, and not the value of voltage? This happens due to the well-known Ohm's law. The human body is not distinguished by precisely defined resistance. Its value depends on a combination of many factors. Therefore, in different situations, dangerous current values can occur at different values of the applied voltage.
Studies have shown that in the vast majority of cases, even under the worst conditions, a voltage of less than 42 V AC is not capable of causing the passage of a dangerous current. That is why this value was chosen when performing work in hazardous conditions when exposed to voltage.
At the same time, there are many power supplies that have a large electromotive force, but are unable to produce a deadly current. This is well known to television masters and car owners.
The voltage at the anode of the kinescope or the electrodes of the spark plug is tens of thousands of volts. When touching these elements, a sensitive and painful electric shock occurs, rarely leading to adverse consequences. Basically, touching high-voltage, but low-current voltage sources is dangerous only for people with a weak heart, since short-term, but strong spasms of the heart muscle occur.
Alternating or direct current is more dangerous and why
It would seem, what does it matter, constant voltage or alternating. However, studies have revealed a pattern that at a frequency of 10-500 Hz, the danger is much higher at the same values than is observed at a constant voltage. This is caused not only by the direct flow of current through the body, but also by its direct effect on the work of the heart muscles. Alternating current causes them to contract uncontrollably. As a result, fibrillation (chaotic contractions) and cardiac arrest occur. Alternating current has several times lower threshold values than direct current, and this is reliably confirmed by experimental data.
Important! With a large value, a constant voltage with a high probability causes an electrolytic effect of the current.
A further increase in frequency carries an equal threat on a par with direct current, but starting from 1000 Hz or more, the danger decreases. Here comes into force the skin effect, which is expressed in the fact that the high-frequency current is displaced closer to outer surface conductor, which in this case is the human body. Thus, with increasing frequency, the probability of current flow in critical directions in the body decreases. Only the thermal effect on the skin increases. Large AC and DC voltages can cause electromagnetic action even in the absence of direct contact. This is expressed in poor health, headaches, malfunctions of pacemakers.
Factors that increase the risk
The dangerous effect of electric current on a person is largely determined by what organs will meet on his way. The most sensitive organs are the heart, brain and lungs. A current flows through the brain when a person’s head gets under the action of voltage, or it touches a grounded area, and an electric shock occurs through any other organ of the body.
The most common touching of elements under hazardous potential is by hand. In the shortest direction of the path of current through the body, this is an arm - an arm or an arm - a leg.
Less dangerous is the case when the discharge passes in the direction of the foot - foot. This happens when you are in the step voltage zone. But there is another danger here. With cramps in the muscles of the legs or fright, a person may fall, and then the current path will pass in a dangerous direction.
Human condition
The state of the human body is importance when determining the dangerous current strength. The work of the polygraph (lie detector) is based on this principle, which, among other parameters, measures the value of the moisture content of the skin. An increase in humidity occurs with excitement, stressful conditions, illness, alcohol or drug intoxication. Different areas of the skin have different sensitivity. For example, the fingertips have much higher electrical resistance values than the skin on the back of the hand.
In these situations, the resistance of the skin is several times higher than in the normal state, so the dangerous values are greatly reduced, and the effect of the electric current will be more pronounced. It is noted that female body has a several times lower threshold of permissible current than the male. But, at the same time, each person has their own unique characteristics in terms of the threshold value.
The impact of electric current on a person, even with the same values, will be less if a person is consciously prepared for an unexpected electric shock. This feature is typical for people who are engaged in professional activities in the maintenance of electrical installations.
The effect of step voltage is dangerous because the danger is not visible from the side, since this voltage is formed as a result of potential spreading along the ground as a result of a break in a high-voltage wire or breakdown of the insulation of an underground high-voltage cable.
The earth layer has a higher resistance than the current-carrying conductor, therefore, at some distance from the place where the wire of the high-voltage line falls or the insulation of the underground cable is broken, a potential difference is formed that reaches dangerous values. The distance on the ground surface at which the potential difference is formed is characterized by the length of a person's step, because the path of the current in the shortest direction passes from one foot to the other. How more value step, the higher the potential difference, and, accordingly, the value of the flowing current. From this we can conclude that in order to safely leave the zone of stress, you do not need to rush and take big steps. On the contrary, the step should be as short as possible. Also, you can not run, because the fall will increase the voltage.
Is static electricity dangerous?
Everyone who wears synthetic clothing is familiar with static electricity. A static voltage charge is generated by the mutual friction of clothes made of various materials, especially wool and synthetics. Upon subsequent contact with a grounded object, for example, a car body, a spark between the body and it jumps from a few millimeters to a centimeter or more in length.
The accumulated potential is several thousand volts, but the amount of current flowing is negligible and causes only a tingling sensation. Static voltage is dangerous for sensitive electronic components, therefore, workers who repair and maintain electronic equipment should wear cotton clothing and special electrostatic bracelets connected to ground to remove the accumulated electrical potential.
Security measures
To reduce the risk of electric shock, special measures have been developed: organizational and technical. The first includes measures aimed at eliminating the appearance of potential on those parts of installations and equipment on which work is carried out. This is the disconnection of current-carrying parts, checking the absence of voltage, fencing elements that are energized and which can be touched, hanging warning and prohibition posters.
Technical activities include:
- Tool with insulating handles;
- Dielectric overalls (gloves, footwear);
- Dielectric mats.
The most important thing is not to touch the conductors, if it is not known for certain whether they are energized or not.
First aid for the injured
The health and life of a person affected by high voltage depends on the timeliness and correctness of actions. The procedure is as follows:
- Stop the effect of electric current on the victim. To do this, turn off the electrical installation. If it is impossible to turn off, release the person from touching the bare conductors by moving the conductor or the victim to the side. In this case, it is imperative to use dielectric gloves, an insulated tool, or, in extreme cases, dry wooden board. If it is impossible to release, you need to cut the wire. The ax must have a dry wooden ax handle. You need to pull the victim by the edge of the clothes, trying not to touch the bare areas of the body, so as not to get an electrical injury yourself;
- Lay the victim on a horizontal flat surface, relax or unfasten the collar of the clothes to improve breathing, check if there is breathing and pulse;
- Immediately call an ambulance by any means;
- If breathing and pulse are present, but the person is unconscious, then you need to bring him to life with a cotton swab moistened with a solution of ammonia;
- If the victim is not breathing, it is necessary to perform artificial ventilation of the lungs until he begins to breathe on his own;
- In the absence of a heartbeat, perform an indirect heart massage.
First first aid must be carried out continuously, until the arrival of the medical team.
Video
The effect of electric current on the human body. Electricity, acting on the human body, can lead to various injuries: electric shock, burns, skin metallization, electrical sign, mechanical damage, electrophthalmia (Table 1).
Table 1. Characteristics of the impact on a person of electric current of various strengths
| Current, mA | AC 50 - 60 Hz | D.C |
| 0,6 — 1,5 | Slight trembling of the fingers | Not felt |
| 2 — 3 | Strong trembling of the fingers | Not felt |
| 5 — 7 | Cramps in the hands | 3day Feeling warm |
| 8 — 10 | Hands with difficulty, but still can be torn off the electrodes. Severe pain in the arms, especially in the hands and fingers | Heating boost |
| 20 — 25 | Hands are paralyzed immediately, it is impossible to tear them off the electrodes. Very severe pain. Difficulty breathing | Even greater increase in heating, slight contraction of the muscles of the hands |
| 50 — 80 | Respiratory paralysis. Beginning of ventricular flutter | Strong feeling of warmth. Contraction of the muscles of the hands. Seizures. Difficulty breathing |
| 90 — 100 | Paralysis of breathing and heart when exposed to more than 0.1 s. | Respiratory paralysis |
electric shock leads to the excitation of living tissues; Depending on the pathological processes caused by electric shock, the following classification of the severity of electrical injuries during electric shock is accepted:
1. electrical injury of the 1st degree- convulsive muscle contraction without loss of consciousness;
2. electrical injury II degree- convulsive contraction of muscles with loss of consciousness, "
3. electrical injury III degree- loss of consciousness and violation of the functions of cardiac activity or respiration (it is possible both);
4. electrical injury IV degree- clinical death.
The severity of electrical damage depends on many factors: the resistance of the body, the magnitude, duration of action, the type and frequency of the current, its path in the body, environmental conditions.
The outcome of electrocution also depends on the physical condition of the person. If he is sick, tired or in a state of intoxication, mental depression, then the action of the current is especially dangerous. Alternating current up to 10 mA and direct current up to 50 mA are considered safe for humans.
Electrical burn various degrees - a consequence of short circuits - in electrical installations and the stay of the body (usually hands) in the sphere of light (ultraviolet) and thermal (infrared) influence of an electric arc; III and IV degree burns with a severe outcome - when a person comes into contact (directly or through an electric arc) with current-carrying parts with a voltage of over 1000 V.
electrical sign(current mark) - specific lesions caused by mechanical, chemical or their combined effects of current. The affected area of the skin is practically painless, there are no inflammatory processes around it. Over time, it hardens and superficial tissues die off. Electrosigns usually heal quickly.
Leather plating- the so-called impregnation of the skin with the smallest vaporous or molten metal particles under the influence of mechanical or chemical action of the current. The affected area of the skin acquires a hard surface and a peculiar color. In most cases, plating heals without leaving marks on the skin. Electrophthalmia is damage to the eyes by ultraviolet rays, the source of which is a voltaic arc. As a result of electrophthalmia, an inflammatory process occurs after a few hours, which disappears if the necessary treatment measures are taken.
In a production environment, electric shock is most often the result of people touching live parts that are under dangerous voltage.
There are two options for such touches with varying degrees of danger. The first, the most dangerous, is the simultaneous touching of two linear wires and the second, less dangerous (there are more such cases) is the touching of one phase.
Single-phase connection to the current circuit: a) with a grounded neutral; b) with isolated neutral
The effects of electric current on a person are extremely diverse in nature and in its types. They depend on many factors.
According to the nature of the impact, there are: thermal, biological, electrolytic, chemical and mechanical damage.
The thermal effect of the current is manifested by burns of individual parts of the body, blackening and charring of the skin and soft tissues; heating to a high temperature of the organs located on the path of the current, blood vessels and nerve fibers. The heating factor causes functional disorders in the organs and systems of the human body.
The electrolytic effect of the current is expressed in the decomposition of various body fluids into ions that violate their properties.
The chemical effect of the current is manifested in the occurrence of chemical reactions in the blood, lymph, nerve fibers with the formation of new substances that are not characteristic of the body.
The biological action leads to irritation and excitation of the living tissues of the body, the occurrence of convulsions, respiratory arrest, and a change in the mode of cardiac activity.
The mechanical action of the current is expressed in a strong contraction of the muscles, up to their rupture, ruptures of the skin, blood vessels, fractures of bones, dislocation of joints, stratification of tissues.
According to the types of injury, there are: electrical injuries and electrical
Electrical injuries are local lesions (burns, electrical signs, skin plating, mechanical damage, electrophthalmia).
Current burns are divided into contact and arc. Contact arise at the point of contact of the skin with the current-carrying part of the electrical installation with a voltage of not more than 2 kV, arc - in places where an electric arc has arisen, which has a high temperature and high energy. The arc can cause extensive body burns, charring, and even complete combustion of large areas of the body.
Electric signs are compacted areas of gray or pale yellow on the surface of a person's skin that has been exposed to current. As a rule, in the place of an electric sign, the skin loses its sensitivity.
Metallization of the skin - the introduction into the upper layers of the skin of the smallest particles of metal, melted under the action of an electric arc or charged particles of electrolyte from electrolysis baths.
Electrophthalmia - inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream ultraviolet radiation from an electric arc. Possible damage to the cornea, which is especially dangerous.
Electric shocks are common lesions associated with the excitation of tissues by the current passing through them (malfunctions in the functioning of the central nervous system, respiratory and circulatory organs, loss of consciousness, speech disorders, convulsions, respiratory failure until it stops, instant death).
According to the degree of impact on a person, there are three threshold current values: perceptible, non-release and fibrillation.
Perceptible is an electric current that, when passing through the body, causes tangible irritation. The sensation from the flow of alternating electric current, as a rule, starts from 0.6 mA.
A non-letting current is called a current that, when passing through a person, causes irresistible convulsive contractions of the muscles of the arms, legs or other parts of the body in contact with the current-carrying conductor. Alternating current of industrial frequency, flowing through the nerve tissues, affects the biocurrents of the brain, causing the effect of "chaining" to an uninsulated current conductor at the point of contact with it. A person cannot independently break away from the current-carrying part.
Fibrillation current is called, which, when passing through the body, causes fibrillation of the heart (simultaneous uncoordinated contractions of individual muscle fibers of the heart). Fibrillation can lead to cardiac arrest and respiratory paralysis.
The degree of electric shock depends on the electrical conductivity or on its inverse parameter - the general electrical resistance of the body. They, in turn, are defined:
Individual characteristics of the human body;
The parameters of the electrical circuit (voltage, strength and type of current, frequency of its oscillations), under the influence of which the employee fell;
By passing current through the human body;
Conditions for inclusion in the power grid;
duration of exposure;
Environmental conditions (temperature, humidity, the presence of conductive dust, etc.).
Low electrical resistance of the body contributes to more severe consequences of the lesion. The electrical resistance of the human body decreases due to unfavorable physiological and psychological conditions (fatigue, illness, alcohol intoxication, hunger, emotional arousal).
The total electrical resistance of the human body is summed from the resistances of each part of the body located on the current path. Each section has its own resistance. The highest electrical resistance has the upper horny layer of the skin, in which there are no nerve endings and blood vessels. With wet or damaged skin, the resistance is about 1000 ohms. With dry skin without damage, it increases many times over. With electrical breakdown of the outer layer of the skin, the total resistance of the human body is significantly reduced. The resistance of the skin falls the faster, the longer the process of current flow.
The severity of a person's injury is proportional to the strength of the current that has passed through his body. A current of more than 0.05 A can fatally injure a person with an exposure duration of 0.1 s.
Alternating current is more dangerous than direct current, but at high voltage (more than 500 V), direct current becomes more dangerous. The most dangerous frequency range of alternating current is from 20 to 100 Hz. The bulk of industrial equipment operates at a frequency of 50 Hz, which is included in this dangerous range. High frequency currents are less dangerous. High-frequency currents can only cause superficial burns, as they only spread over the surface of the body.
The degree of damage to the body largely determines the path in which the electric current passes through the human body. The most frequent in practice options 1, 2, 5, 6, 7, shown in Fig. 2.1.
Rice. 2.1. Options for the passage of electric current through the human body: 1 - "hand-hand" .; 2 - "arm-legs"; 5 - "leg-leg"; 6 - "head-legs"; 7 - "head-hand"
A person touches with both hands current-carrying wires or parts of equipment that are energized. In this case, the movement of current goes from one hand to the other through the lungs and heart. This path is usually called "hand - hand";
A person stands with two feet on the ground and touches the power source with one hand. The path of current flow in this case is called "arm - legs". The current passes through the lungs and possibly through the heart;
A person stands with both feet on the ground in the zone of current draining to the ground from faulty electrical equipment, which in this case acts as a ground electrode. The earth within a radius of up to 20 m receives a voltage potential that decreases with distance from the ground electrode. Each of a person's legs receives a different voltage potential, determined by the distance from the faulty electrical equipment. As a result, an electric circuit "leg - leg" arises, the voltage in which is called stepping;
Touching the head to the current-carrying parts can create a circuit where the current path will be "head - hands" or "head - legs".
The most dangerous are those options, in the implementation of which the vital systems of the body, such as the brain, heart, and lungs, fall into the affected area. These are chains: "head - hand", "head - legs", "hands - legs", "hand - hand".
Example. Alternating current with a frequency of 50 Hz and a voltage of 220 V, which is standard for domestic electrical networks, when passing along the “hand-to-foot” path, depending on the strength of the current, can have different effects. So, if the current strength is 0.6-1.5 mA, it is already noticeable. It is accompanied by slight itching, slight trembling of the fingers. At a current strength of 2.0-2.5 mA, pain and strong trembling of the fingers appear. At a current strength of 5.0-7.0 mA, hand cramps occur. A current of 20.0-25.0 mA is already a non-letting current. A person cannot take his hands off the guide on his own, there are severe pains and convulsions, shortness of breath. At a current strength of 50.0-80.0 mA, respiratory paralysis occurs (with prolonged current flow, cardiac fibrillation may occur). At 90.0-100.0 mA, fibrillation occurs. After 2-3 seconds, respiratory paralysis sets in (Table 2.1).
Table 2.1. The nature of the impact on a person when an electric current flows through the body (parts of the body)
The flow of direct current through the human body with a voltage of less than 500 V causes pain at the point of contact with the conductor, in the joints of the limbs, pain shock, burns. However, it can also lead to respiratory or cardiac arrest. At a voltage of 500 V and above, there are practically no differences in the effects of direct and alternating currents.
There is a non-linear relationship between the current flowing through the human body and the voltage applied to it. As the voltage increases, the current increases faster than the voltage.
The degree of danger of electric shock depends on the conditions for connecting a person to the power grid. In production, three-phase AC electrical networks (with isolated neutral or grounded neutral) and single-phase electrical networks are used. All of them are dangerous, but each has a different degree of danger.
For three-phase AC networks with any neutral mode, the most dangerous is a two-phase touch (simultaneously to two wires of a working network). A person closes two phase wires through his body and falls under the full line voltage of the network. In this case, the current passes along the most dangerous path "hand - hand". The current strength is maximum, since only a very low (about 1000 Ohm) resistance of the human body is included in the network. A two-phase contact with the active parts of the installation even at a voltage of 100 V can be fatal.
If you touch the wire of the installation in emergency mode (breakage of the second wire and short circuit of the phase to ground), due to the redistribution of voltages between the phases, the risk of serious electric shock to a person is somewhat reduced.
Three-phase electrical networks with an earthed neutral are somewhat less dangerous than networks with an isolated neutral. Such networks have very little resistance between neutral and earth, so grounding the neutral serves a safety purpose.
The least dangerous is always touching one of the wires of a working network.
When a broken wire falls to the ground or if the insulation is damaged and a phase breaks through the equipment case to the ground, as well as at the locations of the ground electrode, the fault current spreads in the ground. It obeys the hyperbolic law (Fig. 2.2).
Rice. 2.2. Scheme of the spreading of the fault current in the soil: 1 - the place where the broken wire falls to the ground; 2 - curve (hyperbola) of the distribution of potentials on the surface of the earth during the spreading of current; U3 - voltage at the closing point
Since the ground is a significant resistance to the spreading of current, all points located on the same radial line, but at different distances from the point where the conductor closes to the ground, will have a different potential. It is maximum at the ground electrode, decreases with distance from it and is equal to zero outside the spreading zone. At a distance of 1 m from the ground electrode, the voltage drop in dry soil is already 68%, at a distance of 10 m - 92%. The presence of a person in the area of current spreading close to the ground electrode can be dangerous.
It is necessary to leave the danger zone along the radius in very small steps. According to the "Safety instructions for the operation of traction substations, power supply points and sectioning of electrified railways» No. TsE-402, approved by the Ministry of Railways of Russia on 10/17/96, one should move in the zone of spreading of the ground fault current without means of protection (dielectric galoshes, boots), moving the feet on the ground and not tearing them one from the other. With an increase in the length of the step, the difference in the potentials under which each of the legs is located increases. The voltage formed due to the potential difference in the current spreading zone between two points on the earth's surface, which are separated from each other in the radial direction at a step distance (0.8 m), is called the step voltage. The current path at the step voltage "leg - leg" does not touch the vital organs. However, with significant tension, leg cramps occur, the person falls. In this case, the electrical circuit closes through the entire body of the fallen.
In single-phase direct current networks, the most dangerous is also the touch of a person simultaneously on two wires, since in this case the current flowing through the human body is determined only by the resistance of his body.
The duration of current exposure often serves as a factor on which the outcome of the lesion depends. The longer the electric current acts on the body, the more severe the consequences. After 30 s, the resistance of the human body to the flow of current drops by about 25%, and after 90 s, by 70%.
⇐ PreviousPage 4 of 9Next ⇒
Email the current passing through the human body produces thermal, electrical and mechanical effects, which are the usual physical and thermal process inherent in both living and non-living matter; at the same time El. The current also produces a biological effect, which is a specific process characteristic only of living tissue.
The thermal effect of the current is manifested in burns of individual parts of the body, heating to a high temperature of blood vessels, nerves, heart, brain and other organs that are in the path of the current, which causes functional disorders in them.
The electrical action of the current is expressed in the decomposition of an organic fluid, including blood, which is accompanied by significant disturbances.
The mechanical (dynamic) effect of the current is expressed in stratification, rupture, and other damage to body tissues, including muscle, blood vessel walls of the lung tissue as a result of a dynamic effect, as well as an instantaneous explosive formation of steam from tissue fluid and blood overheated by the current.
The biological effect of current is manifested in irritation and excitation of living tissues of the body, as well as in violation of internal bioelectrical processes occurring in a normally functioning organism.
There are two types of electrical injuries: local, when local damage to the body occurs; general electrical injuries, the so-called electrical shocks, when the entire body is damaged due to disruption of the normal functioning of vital organs and systems.
Local electrical injury is a pronounced violation of the integrity of body tissues in a particular place, including bone tissues, caused by exposure to electric current. current. The danger of local injuries and the complexity of their treatment depends on the location, nature and degree of tissue damage. These are electric burns, electric signs, skin metallization, mechanical damage and electrophthalmia.
Electrical burns are the most common electrical injury: burns occur in approximately 63% of victims of electric shock. current, and 23% of them are accompanied by email. signs and metallization of the skin.
Depending on the conditions of occurrence, two types of burns are distinguished: current or contact and arc.
Current or contact - this burn occurs in electrical installations of relatively low voltage - not higher than 2 kV. With more high voltages, as a rule, an email is formed. an arc or spark, as a result of which a burn of another type occurs - arc. Current burns are formed in 38% of victims of electric. current, in most cases they are burns of I and II degrees; at voltages above 380 V, more severe burns of III and IV degrees also occur.
Arc burn is observed in electrical installations of various voltages. At the same time, in installations up to 6 kV, burns are the result of accidental short circuits, for example, when working under voltage on panels and assemblies up to 1000V, where measurements are made with portable devices (electrical clamps).
An example is a case. When repairing a 380V energized switchboard, el. fitter standing on wooden floor, accidentally closed the knives of the knife switch with a wire. Emerging email. arc caused burns I and II degrees of the face, neck and right hand fitter. However, no current passed through it. The hand burns were caused by the fire of the clothes.
Electric signs, also called current signs or electric marks, are sharply defined gray or pale yellow spots on the surface of a body subjected to current. Usually the signs are round or oval in shape and 1-5 mm in size with a depression in the center. Usually electrical signs are painless and the treatment ends well: over time upper layer the skin comes off and the affected area acquires its original color, elasticity and sensitivity. These signs appear in about 11% of current victims.
Metallization of the skin - the penetration into the upper layers of the skin of the smallest particles of metal, melted under the action of el. arcs. This phenomenon occurs during short circuits, trips of disconnectors and knife switches under load. The affected area of the skin has a rough surface. The victim feels pain from burns on the affected area under the action of the heat of the metal brought into the skin and experiences skin tension from the presence of a foreign body in it. Metallization of the skin is observed in 10% of those affected by e-mail. current. In most cases, an arc burn occurs simultaneously with plating, which almost always causes more severe injuries than plating.
Mechanical damage is in most cases the result of sharp involuntary convulsive muscle contractions under the influence of current passing through the human body. As a result, ruptures of tendons, skin, blood vessels and first tissue can occur; joint dislocations and even bone fractures may occur. Of course, similar injuries caused by a person falling from a height, bruises on objects as a result of current exposure are not considered electrical injuries.
Mechanical damage occurs when working mainly in installations up to 1000V with a relatively long stay of a person under voltage.
As an example case:
During the installation of the substation, the worker took his hand on the mounted busbar, which runs along the wall from top to bottom and turned out to be energized at 220V relative to the ground, as a result of accidental contact with temporary electrical wiring. The worker, experiencing strong convulsive muscle contractions, did not lose consciousness, but could not open his hand and call for help. Under the influence of the current, he stayed for several seconds until he was released by other workers who saw that he was squatting in an uncomfortable position and holding on to the tire with his outstretched hand. According to a medical report, the worker suffered a dislocation of the shoulder and a fracture of the neck of the scapula of the arm.
Electrophthalmia is an inflammation of the outer membranes of the eyes, the cornea and conjunctiva (the mucous membrane that covers the eyeball), resulting from exposure to a powerful stream of ultraviolet rays, which are vigorously absorbed by the cells of the body and cause chemical changes in them.
Electric shock - is a consequence of the flow of current through the human body; at the same time, the entire body is at risk of damage. Depending on the outcome of the lesion, electric shocks can be divided into the following five degrees:
convulsive, barely perceptible muscle contraction;
convulsive muscle contraction, accompanied by severe, barely tolerable pain, without loss of consciousness;
convulsive contraction of muscles with loss of consciousness, but with the preservation of breathing and heart work;
loss of consciousness and impaired heart activity or breathing;
clinical death, i.e. lack of respiration and circulation.
The outcome of the impact email. current on the human body depends on a number of factors, including the value and duration of the passage of current through his body. The type and frequency of the current, as well as on the individual properties of a person. Email a shock, even if it does not lead to death, can cause cardiac disorders in the body, which appear immediately after exposure to the current or after several hours, days and even months.
perceptible current.
A person begins to feel the effect of the current passing through him, on average, about 1.1 mA at an alternating current of 50 Hz and about 6 mA at a constant current. This effect is limited with alternating current to mild itching and slight tingling, and with direct current - a feeling of heating of the skin in the area touching the current-carrying parts.
Does not release current.
An increase in current above a perceptible threshold causes muscle cramps and painful sensations in a person, which increase with increasing current and spread to all large plots body. With an average current of about 15 mA (50 Hz), the pain becomes barely bearable, and the cramps of the muscles of the hands are so significant that a person is not able to overcome them. As a result, he cannot open his hand.
The highest direct current at which a person is still able to withstand the pain that occurs at the moment of tearing off the hands from the electrodes is approximately 50-80 mA. This current is conditionally accepted as the threshold of non-releasing currents at a constant voltage.
Alternating current.
An increase in frequency from 0 to 50 Hz leads to an increase in the danger of injury, but a further increase in frequency, despite the increase in current passing through the body, is accompanied by a decrease in the danger of injury, which completely disappears at 450–500 kHz. Simply put, a current with a frequency of 450-500 kHz cannot cause a fatal injury due to the cessation of the heart or lungs. True, these currents retain the danger of burns.
D.C.
Approximately 4-5 times safer than AC. If with alternating current, according to pain, a person is able to endure 42V, then with direct current 110V. This is because the current passing through the body causes a weaker muscle contraction.
⇐ Previous123456789Next ⇒
Read also:
IMPACT OF ELECTRIC CURRENT ON THE HUMAN BODY. Flowing through the human body, the electric current produces thermal, electrolytic, mechanical and biological effects.
The thermal effect of the current is manifested in burns of individual parts of the body, heating to a high temperature of blood vessels, nerves, heart, brain, and other organs located on the path of the current, which causes serious functional disorders in them (i.e., disorders of the specific activity of organs).
The electrolytic effect of the current is expressed in the decomposition of an organic liquid, including blood, which is accompanied by significant violations of its physicochemical composition.
The mechanical effect of the current is manifested in the occurrence of significant pressure in the blood vessels and tissues of the body during the evaporation of blood and other fluids, as well as in their displacement and mechanical stress under the influence of electrodynamic forces. In this case, severe damage to various tissues and blood vessels can occur.
The biological effect of the current is manifested in the stimulation of internal bioelectrical processes that occur in a normally functioning organism and are closely related to its vital functions. Irritation of living tissues by electric current causes a response in them - excitation, which is one of the main physiological processes and is characterized by the fact that living formations pass from a state of relative physiological rest to a state of activity specific to them. Thus, the excitation of muscle tissue, due to the current passing through it, manifests itself in the form of involuntary muscle contractions, i.e.
The effect of electric current on a person
motor effects. Violation of bioelectric processes is as follows. In living tissue, and primarily in muscles (including the heart muscle), as well as in the central and peripheral nervous systems, electrical potentials constantly arise - biopotentials, which are associated with the emergence and spread of the excitation process, i.e. with the transition living tissue into a state of active activity. An external electric current, acting with a biocurrent, the value of which is very small, can disrupt the normal nature of its action on human tissues and organs, suppress biocurrents and thereby cause specific disorders in the body up to its death.
The table shows data on the passage of current through the human body along the path "hand - hand" or "hand - foot".
The nature of the impact of electric current on the human body
| Current value, mA | Power frequency alternating current | D.C |
| 0,6-1,5 | Slight itching, tingling of the skin under the electrodes | Not felt |
| 2,0-4,0 | Sensation of current spreads to the wrist, slightly reduces the hand | Not felt |
| 5,0-7,0 | Pain aggravate in the hands, accompanied by convulsions. Weak pains - in the whole arm. It is possible to overcome the convulsive contraction of the muscles and open the hand in which the electrode is clamped | Weak feeling of skin heating under the electrode |
| 8,0-10 | Violent pains and cramps in the whole arm. It is difficult, but you can take your hand off the electrode | Increased sensation of skin heating |
| 10-15 | Hardly bearable pains in the whole arm increase with time. Can't take my hand off the electrode |
An even greater increase in the sensation of heating both under the electrodes and in the adjacent areas of the skin |
| 20-25 | Hands are paralyzed instantly, it is impossible to tear them off the electrodes. Severe pain, difficulty breathing | An even greater increase in the heating of the skin, the appearance of a sensation of internal heating. Minor muscle contractions |
| 25-50 | Very severe pain in arms and chest. Breathing is extremely difficult. With prolonged flow of current, respiratory paralysis or a weakening of the activity of the heart with loss of consciousness may occur. | Sensation of intense heat, pain and cramps in the arms. When the hands are separated from the electrodes, hardly tolerable pain occurs as a result of convulsive muscle contraction. |
| 50-80 | Breathing becomes paralyzed after a few seconds. The work of the heart is disrupted. With prolonged current flow, cardiac fibrillation may occur. | Sensation of very strong superficial and internal heating, severe pains in the whole arm and in the chest. Difficulty breathing. Hands cannot be torn off the electrodes due to severe pain at the time of contact failure |
| Fibrillation of the heart after 20-30 s; after a few seconds - respiratory paralysis | ||
| Over 5000 | Breathing is paralyzed immediately - in a fraction of a second. Cardiac fibrillation usually does not occur; temporary cardiac arrest during the current flow is possible. With prolonged current flow (several seconds), severe burns, tissue destruction. Usually fatal |
Products made of dielectrics (rubber, bakelite, electric cardboard, porcelain, etc.) are mainly used as protective equipment against electric shock. In some cases, it is also allowed to use wood boiled in linseed or other drying oil (but not in paraffin) as a protective agent.
In accordance with the safety regulations, all protective equipment according to the degree of reliability, they are divided into basic and additional (Table 83). The main ones are those protective means by which it is allowed to touch live parts under voltage and the insulation of which reliably withstands the operating voltage of electrical installations. Additional protective means are designed to enhance the effect of fixed assets and are used simultaneously with them.
_____________________
Previous123456789101112131415Next
During operation and repair electrical equipment and networks a person can be in the scope electric field or direct contact with energized electrical wiring. As a result of the passage of current through a person, a violation of his vital functions can occur.
The risk of electric shock is exacerbated by the fact that, Firstly, the current has no external signs and, as a rule, a person without special devices cannot detect the danger threatening him in advance; Secondly, the impact of current on a person in most cases leads to serious violations of the most important vital systems, such as the central nervous, cardiovascular and respiratory, which increases the severity of the lesion; third, alternating current can cause intense muscle cramps, leading to a non-release effect, in which a person cannot independently free himself from the effects of current; fourthly, the impact of current causes a sharp reaction in a person, and in some cases loss of consciousness, which, when working at height, can lead to injury as a result of a fall.
Electric current, passing through the human body, can have biological, thermal, mechanical and chemical effects. Biological action is the ability of electric current to irritate and excite living tissues of the body, thermal- in the ability to cause burns to the body, mechanical- lead to tissue rupture, and chemical to blood electrolysis.
The impact of electric current on the human body can cause electrical injury. Electrical injury is an injury caused by exposure to an electric current or electric arc. Conventionally, electrical injuries are divided into local and general. At local electrical injuries local damage to the body occurs, expressed in the appearance of electrical burns, electrical signs, metallization of the skin, mechanical damage and electrophthalmia (inflammation of the outer membranes of the eyes). General electrical injuries, or electric shocks, lead to damage to the whole organism, expressed in violation or complete cessation of the activity of the most vital organs and systems - lungs (respiration), heart (circulation).
……………….
The effect of electric current on the human body
1.1 Types of electric shock
Passing through the body, the electric current produces 3 types of effects: thermal, electrolytic and biological.
The thermal effect is manifested in burns of external and internal parts of the body, heating of blood vessels and blood, etc., which causes serious functional disorders in them.
Electrolytic in the decomposition of blood and other organic fluids, thereby causing significant violations of their physico-chemical compositions and tissue as a whole.
The biological effect is expressed in irritation and excitation of the living tissues of the body, which may be accompanied by involuntary convulsive muscle contractions, including the muscles of the heart and lungs. In this case, various disorders can occur in the body, including mechanical damage to tissues, as well as a violation and even complete cessation of the activity of the respiratory and circulatory organs.
There are two main types of damage to the body: electrical trauma and electrical shock. Often both types of damage accompany each other. However, they are different and should be considered separately.
1.1.1 Electrical injury
Electrical injuries are clearly expressed local violations of the integrity of body tissues caused by exposure to electric current or an electric arc. Usually these are superficial injuries, that is, lesions of the skin, and sometimes other soft tissues, as well as ligaments and bones.
The danger of electrical injuries and the complexity of their treatment are determined by the nature and degree of tissue damage, as well as the body's response to this damage.
Usually, injuries are cured, and the victim's working capacity is restored completely or partially. Sometimes (usually with severe burns) a person dies.
§ 1. The effect of electric current on a person and types of lesions.
In such cases, the immediate cause of death is not electric current, but local damage to the body caused by current. Characteristic species electrical injuries electrical burns, electrical signs, skin plating and mechanical damage.
Electric burn is the most common electrical injury: burns occur in most of the victims of electric current (60-65%), and a third of them are accompanied by other injuries, signs, metallization of the skin and mechanical damage.
Depending on the conditions of occurrence, there are three types of burns:
- current, or contact, arising from the passage of current directly through the human body as a result of human contact with the current-carrying part; this type of burn occurs in electrical installations of relatively low voltage not higher than 1-2 kV and is, as a rule, a skin burn, that is, external damage;
- arc, due to the impact on the human body of an electric arc, but without the passage of current through the human body; usually these burns are the result of accidental short circuits in electrical installations from 220 to 6000 V, for example, when working under voltage on panels and assemblies, when performing measurements with portable devices, etc.;
- mixed, which is the result of the action of both of these factors simultaneously, that is, the action of an electric arc and the passage of current through the human body; this burn occurs, as a rule, in higher voltage installations above 1000 V. In this case, an arc is formed between the current-carrying part and a person, and a current that is usually of great importance (several amperes and even tens of amperes) passes through the human body. In this case, the lesions are severe and often end in the death of the victim, and the severity of the injury increases with the voltage of the electrical installation.
Electric signs, also called current signs or electric marks, are clearly defined spots of gray or pale yellow color on the surface of the skin of a person who has been exposed to current. Often signs are round or oval with a depression in the center; the sizes of signs are 1-5 mm. The affected area of the skin hardens like a callus.
⇐ Previous52535455565758596061Next ⇒
Publication date: 2015-11-01; Read: 518 | Page copyright infringement
Studopedia.org - Studopedia.Org - 2014-2018. (0.001 s) ...
Impact of electric current
On the human body
When designing and implementing grounding devices (GD), the probability of injury to a person by electric current is taken into account, since it is impossible to exclude the contact of people with dangerous voltages, the appearance of which is possible on parts of electrical installations that are not normally energized. That's why in order to ensure the safety of people performed protective earth . The effect of electric current on the human body depends on its magnitude, duration And way through which it passes, as well as from physical condition of a person. The greatest danger is current passing through the region of the heart.
The effects of electric current on the human body are extremely diverse. They depend on many factors.
By the nature of the impact distinguish: thermal, biological, electrolytic, chemical and mechanical damage.
thermal the impact of current is manifested by burns of individual parts of the body; blackening and charring of the skin and soft tissues; heating to a high temperature of organs located on the path of electric current, blood vessels and nerve fibers, causing functional disorders in them.
electrolytic the effect of the current is manifested in the decomposition of various body fluids into ions, violating their properties.
Chemical the impact of the current is expressed in the occurrence of chemical reactions in the blood, lymph, nerve fibers with the formation of new substances that are unusual for the body.
biological the effect of current is manifested in irritation and excitation of body tissues, the occurrence of convulsions, respiratory arrest, and a change in the mode of cardiac activity.
mechanical the impact of the current leads to strong contractions of the muscles, up to their rupture, to ruptures of the skin, blood vessels, bone fractures, dislocations of the joints, stratification of tissues.
By type of injury Distinguish between electrical injury and electrical shock.
electrical injury- these are local lesions (burns, electrical signs, skin metallization, mechanical damage, electrophthalmia).
Electric shocks- these are general lesions associated with the excitation of tissues by the current passing through them (disturbances in the functioning of the central nervous system, respiratory and circulatory organs, loss of consciousness, speech disorder, convulsions, respiratory failure, up to stop, immediate death).
By degree of impact on the human body are distinguished three current thresholds: palpable, unrelenting And fibrillatory.
palpable is called an electric current, which, when passing through the human body, causes tangible irritation. The feeling of flowing alternating electric current, as a rule, starts from a value of 0.6 mA.
Not letting go called the current, which, when passing through the human body causes irresistible convulsive contractions of the muscles of the hands, legs or other parts of the body in contact with a live conductor. Alternating current of industrial frequency, flowing through the nerve fibers, absorbs the control biocurrents of the cerebral cortex, which leads to the effect of "chaining" to the place of touch. A person cannot independently break away from the current-carrying part of the conductor.
Fibrillatory is called a current that, when passing through the human body, causes fibrillation of the heart - non-coordinated contractions of individual muscle fibers of the heart at different times, ultimately leading to to cardiac arrest And respiratory paralysis.
Degree of electric shock depends on:
- general electrical resistance or its inverse parameter - the conductivity of the body, which depend on the individual characteristics of the human body;
− parameters of the electrical circuit (voltage, strength and type of current, frequency of oscillations), under the action of which a person fell;
− paths of current passing through the human body;
− conditions for inclusion in the power grid;
− duration of exposure;
− environmental conditions (temperature, humidity, presence of conductive dust, etc.).
Low electrical resistance of the body contributes to more severe consequences of electric shock. Electrical resistance of the human body reduce such indicators. how physiological And psychological condition(fatigue, alcohol intoxication, hunger, illness, emotional arousal).
The total electrical resistance of the human body is summed from the resistances of each of the parts of the body located on the current path.
Alternating current is more dangerous than permanent, however at high voltage (more than 500 V) direct current becomes more dangerous.
The path of electric current through the human body largely determines degree of damage organism.
The most common options in practice are shown in Figure 9.8:
Fig.9.8. Options for the passage of electric current through the human body:
1 - "hand-hand"; 2 - "arm-legs"; 3 - "arm-leg"; 4 - "arms and legs"; 5 - "leg-leg";
6 - "head-legs"; 7 - "head-hand"
most dangerous are those options in which vital organs and systems of the body fall into the affected area – brain , heart, lungs . These are chains: "head-hands"; "head-legs"; "hands-legs"; "hand-hand".
The effect of current on the human body, provided it passes through the paths "hand-hand" and "hand-foot" is presented in table 9.5.
Table 9.5.
The nature of the impact of electric current on the body
Human.
| Current value, mA | The nature of the impact | |
| AC 50 Hz | D.C | |
| 0,6 – 1,6 | Threshold of sensation (beginning of sensation) - slight itching, tingling of the skin under the conductors | Not felt |
| 2 – 4 | The sensation of current extends to the wrist, slightly reduces the hand | Not felt |
| 5 – 7 | Pain intensifies in the entire hand, accompanied by convulsions; weak pains are felt in the whole arm, up to the forearm. Hands, as a rule, can be torn off the conductors. | Threshold of sensation (beginning of sensation) - itching, the impression of heating the skin under the conductor |
| 8 – 10 | Severe pain with cramps in the whole arm, including the forearm. Hands are difficult, but in most cases can still be torn off the conductors |
Increased feeling of warmth |
| 10 – 15 | Non-release currents - irresistible convulsive contractions of the muscles of the hand in which the conductor is clamped. Hardly bearable pains in the whole arm. With an increase in the duration of the flow of the current, the pain intensifies. | An even greater increase in the sensation of heating both under the conductor and in the adjacent areas of the skin. |
| 20 – 25 | Hands are paralyzed instantly, it is impossible to break away from the conductors. Severe pain, breathing is difficult. | An even greater increase in the sensation of heating the skin, the appearance of a sensation of internal heating. Slight contraction of the muscles of the hands. |
| 25 – 50 | Very severe pain in arms and chest. Breathing is extremely difficult. With prolonged current, respiratory paralysis or a weakening of the activity of the heart with loss of consciousness may occur. | Sensation of intense heat, pain and cramps in the arms. When the hands are separated from the conductors, barely tolerable pain occurs as a result of convulsive muscle contraction. |
| 50 – 80 | Respiratory paralysis after a few seconds, the work of the heart is disturbed. With prolonged current flow, cardiac fibrillation may occur. | Non-release currents - hands cannot be torn off the conductors due to severe pain when contact is broken. Sensation of very strong superficial and internal heating, severe pains in the whole arm and in the chest. Difficulty breathing. |
| heart failure. | Respiratory paralysis with prolonged current flow | |
| Same action in less time | Fibrillation of the heart after 2-3s; after a few more seconds - heart failure. | |
| Over 500 | Breathing is paralyzed immediately - in a fraction of a second. Fibrillation of the heart, as a rule, does not occur; possible temporary cardiac arrest during the current flow. With prolonged current flow (several seconds), severe burns, tissue destruction. |
The most characteristic are the following currents: threshold palpable, threshold non-rejection, threshold fibrillation.
Threshold sensible current- this is the smallest value of the sensible current, i.e. current, which causes tangible irritations when passing through the body. Its value at 50 Hz is 0.6 - 1.5 mA. At the same time, only 1 person feels the current of 0.63 mA. out of a thousand. 1.59 mA - 999 people
Topic 12. The effect of electric current on the human body, analysis of electrical safety conditions
out of a thousand and 1.11 mA - 500 people. out of a thousand, i.e. fifty %.
Threshold non-release current- this is the smallest value of the transmitting current, i.e., the current that causes, when passing through a person, irresistible convulsive contractions of the muscles of the hand in which the conductor is clamped. Its value at 50 Hz is 5 - 25 mA. At the same time, the current of 5.3 mA is non-releasing only for 1 person. out of a thousand, 24.6 mA - for 999 people. out of a thousand and 14.9 mA - for 500 people. out of a thousand, i.e. for 50% of people.
Threshold fibrillation current- this is the smallest value of the fibrillation current, i.e., the current that causes fibrillation of the heart when passing through the body. Its value at 50 Hz is 50 - 350 mA. At the same time, a current of 67 mA causes fibrillation in only 1 person. out of a thousand, 367 mA - in 999 people. out of a thousand and a current of 157 mA - for 500 people. out of a thousand, i.e., 50% of people.
fibrillation of the heart- violation of the normal heart rhythm. This condition is characterized by uncoordinated, asynchronous contractions of the muscular fibril tissue of the heart. During fibrillation, the heart is not damaged, but the rhythm of its work is disturbed, it does not beat, but trembles. The circulation of blood in the body stops, and death occurs within a few minutes.
Introduction
The electrical saturation of modern production creates an electrical hazard, the source of which can be electrical networks, electrified equipment and tools, computer and organizational equipment that runs on electricity. This determines the relevance of the problem of electrical safety - the elimination of electrical injuries.
Electrical safety is a system of organizational and technical measures and means that ensure the protection of people from the harmful and dangerous effects of electric current, electric arc, electromagnetic field and static electricity.
In comparison with other types of industrial injuries, electrical injuries make up a small percentage, however, it occupies one of the first places in terms of the number of injuries with a severe and especially fatal outcome.
An analysis of industrial injuries in the meat industry shows that, on average, about 18% of all severe and fatal cases occur as a result of electric shock.
The largest number of electrical injuries (60-70%) occurs at work on electrical installations with voltage up to 1000 V. This is due to the wide distribution of such installations and the relatively low level of training of those operating them. There are much fewer electrical installations over 1000 V in operation and they are serviced by specially trained personnel, which causes a smaller number of electrical injuries.
1. The effect of electric current on the human body
Electric current, passing through the human body, has a biological, electrolytic, thermal and mechanical effect.
The biological effect of current is manifested in irritation and excitation of tissues and organs. This results in seizures skeletal muscle, which can lead to respiratory arrest, avulsion fractures and dislocations of the limbs, spasm of the vocal cords.
The electrolytic effect of the current is manifested in the electrolysis (decomposition) of liquids, including blood, and also significantly changes the functional state of cells.
The thermal effect of electric current leads to burns of the skin, as well as the death of subcutaneous tissues, up to charring. The mechanical action of the current is manifested in the stratification of tissues and even the separation of body parts.
There are two main types of damage to the body: electrical trauma and electrical shock. Often both types of damage accompany each other. However, they are different and should be considered separately.
Electrical injuries are clearly defined local violations of the integrity of body tissues caused by exposure to electric current or an electric arc. Usually these are superficial injuries, that is, lesions of the skin, and sometimes other soft tissues, as well as ligaments and bones.
The danger of electrical injuries and the complexity of their treatment are determined by the nature and degree of tissue damage, as well as the body's response to this damage. Usually, injuries are cured, and the victim's working capacity is restored completely or partially.
Sometimes (usually with severe burns) a person dies. In such cases, the immediate cause of death is not electric current, but local damage to the body caused by current.
Typical types of electrical injuries are electrical burns, electrical signs, skin plating, electrophthalmia and mechanical damage.
Electrical burns are the most common electrical injury. They make up 60-65%, and 1/3 of them are accompanied by other electrical injuries.
There are burns: current (contact) and arc.
Contact electrical burns, i.e. tissue damage at the points of entry, exit and on the path of electric current flow occurs as a result of human contact with the current-carrying part. These burns occur during the operation of electrical installations of relatively low voltage (not higher than 1-2 kV), they are relatively light.
An arc burn is caused by the action of an electric arc that creates a high temperature. Arc burn occurs when working in electrical installations of various voltages, often the result of accidental short circuits in installations from 1000 V to 10 kV or erroneous operations of personnel. The defeat arises from a change in the electric arc or clothing caught fire from it.
There may also be combined lesions (contact electric burn and thermal burn from the flame of an electric arc or ignited clothing, electric burn in combination with various mechanical damage, electric burn simultaneously with thermal burn and mechanical injury).
Electric signs are clearly defined spots of gray or pale yellow color on the surface of the skin of a person who has been exposed to current. Signs are round or oval with a depression in the center. They come in the form of scratches, small wounds or bruises, warts, skin hemorrhages, and calluses. Sometimes their shape corresponds to the shape of the current-carrying part that the victim touched, and also resembles the shape of wrinkles.
In most cases, electrical signs are painless, and their treatment ends safely: over time, the top layer of the skin and the affected area acquire their original color, elasticity and sensitivity. Signs occur in about 20% of those affected by the current.
Metallization of the skin is the penetration into its upper layers of particles of metal that has melted under the action of an electric arc. This is possible in case of short circuits, trips of disconnectors and knife switches under load, etc.
The affected area has a rough surface, the color of which is determined by the color of the metal compounds that have fallen under the skin: green - in contact with copper, gray - with aluminum, blue-green - with brass, yellow-gray - with lead. Usually, over time, the diseased skin disappears and the affected area becomes normal. At the same time, all the painful sensations associated with this injury also disappear.
Metallization of the skin is observed in approximately one in ten of the victims. Moreover, in most cases, simultaneously with metallization, an electric arc burn occurs, which almost always causes more severe injuries.
Electrophthalmia is an inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of ultraviolet rays, causing chemical changes in the cells of the body. 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. Electrophthalmia occurs relatively rarely (in 1-2% of victims), most often during electric welding.
Mechanical damage is the result of sharp, involuntary convulsive muscle contractions under the influence of a current passing through a person. As a result, ruptures of the skin, blood vessels and nervous tissue can occur, as well as dislocations of the joints and even bone fractures. These injuries are usually serious injuries that require long-term treatment. Fortunately, they rarely occur - no more than 3% of those affected by the current.
Electric shock is the excitation of living tissues by an electric current passing through the body, accompanied by involuntary convulsive muscle contractions.
Depending on the outcome of the negative impact of current on the body, electric shocks can be conditionally divided into the following 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 impaired cardiac activity or respiration (or both);
IV - clinical death, that is, the lack of breathing and blood circulation.
Clinical (or "imaginary") death is a transitional period from life to death, occurring from the moment of cessation of activity and lungs. In a person who is in a state clinical death, there are no signs of life, he does not breathe, his heart does not work, pain stimuli do not cause any reactions, the pupils of the eyes are dilated and do not react to light. However, during this period, life in the body has not yet completely died out, because its tissues do not die immediately and the functions of various organs do not immediately die out.
The cells of the brain, which are associated with consciousness and thinking, are the first to die, which are very sensitive to oxygen starvation. Therefore, the duration of clinical death is determined by the time from the moment of cessation of cardiac activity and respiration until the onset of death of the cells of the cerebral cortex; in most cases, it is 4-5 minutes, and when a healthy person dies from an accidental cause, for example, from an electric current, it is 7-8 minutes.
Biological (or true) death is an irreversible phenomenon characterized by the cessation of biological processes in the cells and tissues of the body and the breakdown of protein structures; it occurs after the period of clinical death.
Causes of electrocution death include cardiac arrest, respiratory arrest, and electrical shock.
The cessation of cardiac activity is a consequence of the effect of current on the heart muscle. Such an effect can be direct, when the current flows directly in the region of the heart, and reflex, that is, through the central nervous system, when the current path lies outside this area. In both cases, cardiac arrest can occur or its fibrillation occurs, that is, chaotically fast and different-time contractions of the fibers (fibrils) of the heart muscle, in which the heart stops working as a pump, as a result of which blood circulation in the body stops.
The cessation of breathing as the root cause of death from electric current is caused by a direct or reflex effect of the current on the muscles of the chest involved in the breathing process. A person begins to experience breathing difficulties already at a current of 20-25 mA (50 Hz), which increases with increasing current. With prolonged exposure to current, asphyxia can occur - suffocation as a result of a lack of oxygen and an excess of carbon dioxide in the body.
Electric shock is a kind of severe neuro-reflex reaction of the body in response to strong irritation with an electric current, accompanied by dangerous disorders of blood circulation, respiration, metabolism, etc.
The state of shock lasts from several tens of minutes to a day. After that, either the death of the body may occur as a result of the complete extinction of vital functions or complete recovery as a result of timely active therapeutic intervention.
2. Factors affecting the outcome of human electric shock
The severity of electric shock depends on a number of factors: the value of the current strength, the electrical resistance of the human body and the duration of the current flowing through it, the path of the current, the type and frequency of the current, individual human properties and conditions environment,
The strength of the current is the main factor that determines one or another degree of damage to a person (path: hand-hand, hand-feet).
Fibrillation is called chaotic and multi-temporal contractions of the fibers of the heart muscle, completely disrupting its work as a pump. (For women, the current threshold values are 1.5 times less than for men).
Direct current is about 4-5 times safer than 50 Hz alternating current. However, this is typical for relatively low voltages (up to 250-300 V). At higher voltages, the danger of direct current increases.
In the voltage range of 400-600 V, the danger of direct current is almost equal to the danger of alternating current with a frequency of 50 Hz, and at a voltage of more than 600 V, direct current is more dangerous than alternating current.
The electrical resistance of the human body with dry, clean and intact skin at a voltage of 15-20 V is in the range from 3,000 to 100,000 ohms, and sometimes more.
When the upper layer of the skin is removed, the resistance decreases to 500-700 ohms. When the skin is completely removed, the resistance of the internal tissues of the body is only 300-500 ohms.
When calculating, the resistance of the human body is taken equal to 1000 ohms. If there are various injuries on the skin (abrasions, cuts, abrasions), the
its electrical resistance in these places. The electrical resistance of the human body decreases with an increase in current and the duration of its passage due to increased local heating of the skin, which leads to vasodilation, and, consequently, to an increase in the supply of blood to this area and an increase in sweating.
With an increase in the voltage applied to the human body, the resistance of the skin decreases, and, consequently, the total resistance of the body, which approaches its own. the smallest value 300-500 Ohm. This is due to the breakdown of the stratum corneum of the skin, an increase in the current passing through it, and other factors.
The resistance of the human body depends on the sex and age of people: in women this resistance is less than in men, in children it is less than in adults, in young people it is less than in the elderly. This is due to the thickness and degree of coarsening of the upper layer of the skin. A short-term (for several minutes) decrease in the resistance of the human body (20-50%) causes external, unexpected physical irritations: pain (blows, injections), light and sound.
The electrical resistance is also affected by the type of current and its frequency. At frequencies of 10-20 kHz, the upper layer of the skin practically loses its resistance to electric current.
In addition, there are particularly vulnerable areas of the body to the action of electric current. These are the so-called acupuncture zones (the area of the face, palms, etc.) with an area of 2-3 mm2. Their electrical resistance is always less than the electrical resistance of the zones lying outside the acupuncture zones.
The duration of the current flow through the human body greatly affects the outcome of the lesion due to the fact that over time the resistance of the human skin decreases, and heart damage becomes more likely.
The path of the current through the human body is also essential. The greatest danger arises with the direct passage of current through the vital organs.
Statistics show that the number of injuries with loss of consciousness during the passage of current along the "right arm-leg" path is 87%; along the “leg-leg” path - 15%, The most characteristic current circuits through a person are: arm-legs, arm-arm, arm-torso (respectively 56.7; 12.2 and 9.8% of injuries). But the most dangerous are those current circuits in which both hands are involved - both legs, left arm-legs, arm-arm, head-legs.
The type and frequency of the current also affect the degree of damage. The most dangerous is alternating current with a frequency of 20 to 1000 Hz. Alternating current is more dangerous than direct current, but this is typical only for voltages up to 250-300 V; at high voltages, direct current becomes more dangerous. With an increase in the frequency of the alternating current passing through the human body, the impedance of the body decreases, and the passing current increases. However, a decrease in resistance is possible only within frequencies from 0 to 50-60 Hz.
A further increase in the frequency of the current is accompanied by a decrease in the danger of damage, which completely disappears at a frequency of 450-500 kHz. But these currents can cause burns both when an electric arc occurs, and when they pass directly through the human body. The decrease in the risk of electric shock with increasing frequency is practically noticeable at a frequency of 1000-2000 Hz.
The individual properties of a person and the state of the environment also have a noticeable effect on the severity of the lesion.
3. Conditions and causes of electric shock
The defeat of a person by electric current or electric arc can occur in the following cases:
with a single-phase (single) touch of a person isolated from the earth to non-insulated live parts of electrical installations that are energized;
when a person simultaneously touches two non-insulated parts of electrical installations that are energized;
when approaching a person who is not isolated from the ground, at a dangerous distance to current-carrying parts of electrical installations that are not protected by insulation, which are energized;
when a person who is not isolated from the ground touches non-current-carrying metal parts (cases) of electrical installations that are energized due to a short circuit on the case;
under the action of atmospheric electricity during a lightning discharge;
as a result of the action of an electric arc;
when releasing another energized person.
The following causes of electrical injuries can be distinguished:
Technical reasons - non-compliance of electrical installations, protective equipment and devices with safety requirements and conditions of use, associated with defects in design documentation, manufacturing, installation and repair;
malfunctions of installations, protective equipment and devices that occur during operation.
Organizational and technical reasons - non-compliance with technical safety measures at the stage of operation (maintenance) of electrical installations; untimely replacement of faulty or obsolete equipment and the use of installations that have not been put into operation in the prescribed manner (including home-made ones).
Organizational reasons - non-fulfillment or incorrect fulfillment of organizational security measures, inconsistency of the work performed with the task.
Organizational and social reasons:
overtime work (including work to eliminate the consequences of accidents);
inconsistency of the work of the specialty;
violation of labor discipline;
admission to work on electrical installations of persons under 18 years of age;
attraction to work of persons who have not been issued an order for employment in an organization;
admission to work of persons with medical contraindications.
When considering the causes, it is necessary to take into account the so-called human factors. These include both psychophysiological, personal factors (a person’s lack of individual qualities necessary for this work, a violation of his psychological state, etc.), and socio-psychological (unsatisfactory psychological climate in the team, living conditions, etc.).
4. Measures for protection against electric shock
According to requirements normative documents, the safety of electrical installations is ensured by the following main measures:
1) inaccessibility of live parts;
2) proper, and in some cases increased (double) insulation;
3) grounding or grounding of electrical equipment cases and elements of electrical installations that may be energized;
4) reliable and fast automatic protective shutdown;
5) the use of low voltages (42 V and below) to power portable current collectors;
6) protective separation of circuits;
7) blocking, warning signaling, inscriptions and posters;
8) the use of protective equipment and devices;
9) carrying out scheduled preventive repairs and preventive testing of electrical equipment, apparatus and networks in operation;
10) carrying out a number of organizational activities (special training, certification and re-certification of electrical personnel, briefings, etc.).
To ensure electrical safety at the enterprises of the meat and dairy industry, the following technical methods and means of protection are used: protective grounding, zeroing, the use of low voltages, winding insulation control, personal protective equipment and safety devices, protective shutdown devices.
Protective earth is an intentional electrical connection to earth or its equivalent to non-current-carrying metal parts that may be energized. It protects against electric shock when touching the metal cases of the equipment, the metal structures of the electrical installation, which, due to the violation of electrical insulation, are energized.
The essence of protection lies in the fact that during a short circuit, the current passes through both parallel branches and is distributed between them in inverse proportion to their resistances. Since the resistance of the person-to-ground circuit is many times greater than the resistance of the body-to-ground circuit, the current flowing through the person is reduced.
Depending on the location of the grounding conductor relative to the equipment to be grounded, remote and contour grounding devices are distinguished.
Remote grounding switches are located at some distance from the equipment, while the grounded enclosures of electrical installations are on the ground with zero potential, and a person, touching the enclosure, is under the full voltage of the grounding conductor.
Low voltage - a voltage not exceeding 42 V, used to reduce the risk of electric shock. Small AC voltages are obtained using step-down transformers. It is used when working with portable power tools, when using portable lamps during installation, dismantling and repair of equipment, as well as in remote control circuits.
Isolation of the workplace is a set of measures to prevent the occurrence of a human-ground current circuit and increase the value of the transient resistance in this circuit. This protective measure is applied in cases of increased risk of electric shock and usually in combination with an isolating transformer.
There are the following types of insulation:
working - electrical insulation of the current-carrying parts of the electrical installation, ensuring its normal operation and protection against electric shock;
additional - electrical insulation provided in addition to the working insulation to protect against electric shock in case of damage to the working insulation;
double - electrical insulation, consisting of working and additional insulation. Double insulation consists in one electrical receiver of two stages of insulation independent of each other (for example, covering electrical equipment with a layer of insulating material - paint, film, varnish, enamel, etc.). The use of double insulation is most rational when, in addition to the working electrical insulation of current-carrying parts, the body of the power receiver is made of insulating material (plastic, fiberglass).
Protective shutdown is a fast-acting protection that provides automatic shutdown of an electrical installation in the event of a danger of electric shock in it.
Devices (apparatus) for protective shutdown with respect to the reliability of operation must meet special technical requirements. Personal protective equipment is divided into insulating, auxiliary and enclosing.
Insulating protective equipment provides electrical isolation of a person from current-carrying parts and earth. They are divided into basic (insulated gloves, tools with insulated handles) and additional (insulated galoshes, rugs, coasters)
Auxiliary ones include glasses, gas masks, masks designed to protect against light, thermal and mechanical influences.
Fencing includes portable shields, cages, insulating pads, portable grounding and posters. They are intended mainly for temporary fencing of current-carrying parts, which may be touched by workers.
5. Rendering PP in case of electric shock
All personnel servicing electrical installations must be trained annually in the methods of release from electric current, performing artificial respiration and external heart massage. Classes are conducted by competent medical personnel with training of practical actions on simulators. The head of the enterprise is responsible for the organization of training.
If a person touches live parts under voltage with his hand, then this causes an involuntary convulsive contraction of the muscles of the hand, after which he is no longer able to free himself from live parts. Therefore, the first action of the person providing assistance is the immediate shutdown of the electrical installation, which the victim touches. Shutdown is carried out using switches, knife switches, turning out plugs and other methods. If the victim is at a height, then when turning off the installation, make sure that he does not fall.
If it is difficult to turn off the installation, then it is necessary to free the victim, using all means of protection, so as not to be energized yourself.
At voltages up to 1000 V, you can use a dry board or stick to free the victim from the wire that has fallen on him. You can also pull on dry clothes, while avoiding touching metal parts and open areas the victim's body; it is necessary to act with one hand, holding the other behind the back. It is most reliable for the assisting person to use dielectric gloves and rubber mats when releasing the victim. After releasing the victim from the action of electric current, it is necessary to assess the condition of the victim in order to provide appropriate first aid.
If the victim is conscious, breathing and pulse are stable, then it is necessary to lay him on the bed; unfasten clothes; create a tributary fresh air; create complete peace by observing the breath and pulse. In no case should the victim be allowed to move, as deterioration may occur. Only a doctor can decide what to do next. If the victim breathes very rarely and convulsively, but his pulse is felt, it is necessary to immediately start artificial respiration.
If the victim has no consciousness, breathing, pulse, pupils are dilated, then we can assume that he is in a state of clinical death. In this case, it is urgent to start reviving the body with the help of artificial respiration according to the “mouth-to-mouth” method and external heart massage. If, within only 5-6 minutes after the cessation of cardiac activity, one does not begin to revive the body of the victim, then without oxygen in the air, brain cells die and death passes from clinical to biological; the process becomes irreversible. Therefore, the five-minute time limit is a critical factor in animating.
With the help of an indirect heart massage in combination with artificial respiration, anyone can bring the victim back to life or time will be won before the arrival of the resuscitation team.
Conclusion
The development of technology changes the working conditions of a person, but does not make them safer, on the contrary, in the process of operating new equipment, previously unknown dangerous factors often appear.
Modern production is unthinkable without the widespread use of the electric power industry. Perhaps there is no such professional activity where electric current would not be used.
Negative consequences for human health during operation technological equipment, have now put forward the provision of industrial safety in production as one of the most acute technical and socio-economic problems. The worst consequence of an electric shock is death. Fortunately, it happens quite rarely in this case.
To prevent electrical shock and ensure electrical safety in production, the following are used: insulation of wires and other components of electrical circuits, instruments and machines; protective grounding; zeroing, emergency power off; personal protective equipment and some other measures.
Unfortunately, the widespread aging of production assets, dilapidation of premises has a negative impact on the quality of electrical wiring. Breakdowns in electrical wiring lead not only to electric shocks, but are also one of the main causes of fires.
The influence of the Internet on a person
Types of seizures Tonic-clonic seizures in children
Profession Internet project manager
best remedy for prostatitis
Symptoms and treatment of mastopathy of the mammary glands