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 is an inflammation of the outer membranes of the eyes as a result of exposure to a powerful stream of 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.
Degree of damage electric shock depends on the electrical conductivity or on its inverse parameter - the total electrical resistance of the body. They, in turn, are defined:
Individual characteristics of the human body;
parameters 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 Electricity of the net alternating current (with isolated neutral or grounded neutral) and single-phase electrical networks. 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 grounding conductor, 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, move in the area of spreading of the ground fault current without protective equipment (dielectric galoshes, boots) follows, 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 DC networks, the most dangerous is also a person’s touching two wires at the same time, 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%.
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Ministry of Transport of the Russian Federation
Federal State Budgetary Educational Institution of Higher Professional Education
"Ulyanovsk Higher Aviation School of Civil Aviation (Institute)"
Department of Search and Rescue Flight Support
Essay
Factors that determine the risk of electric shock
Compiled by: Dyachenko M.V.
Head: Shurekov V.V.
Ulyanovsk 2014
Introduction
1. The effect of electric current on the human body
1.1 Types of electric shock
1.2 Electric shock
1.3 Electrical resistance of the human body
1.4 Main factors influencing the outcome of electric shock
2. Conditions and causes under which electric shock occurs
3. Measures to ensure electrical safety in production
3.1 Organizational safeguards
3.2 Organizational and technical protection measures
Conclusion
List of used literature
INconducting
Russia is a working country. According to statistics for January 2014, the economically active population in Russia is 52% (74.6 million people). Percentage of unemployed as of January 2014 is 5.6%, i.e. 4.2 million people Thus, there are 70.4 million people working in our country.
It is noteworthy that almost all professions today in one way or another come into contact with the use of electricity.
Electric current poses a serious danger to human life, so the task of ensuring electrical safety is very, very serious.
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.
Distinguish between direct and alternating current. Today, the use of alternating current with a frequency of 50 Hz to 300 GHz is common.
Let's analyze this range in more detail:
1. Industrial frequency current, 50 Hz, is used in industrial and domestic electrification systems.
2. Low frequency current, 3-300 kHz - in radio broadcasting, during melting, welding, heat treatment of metals.
3. Medium frequency current, 0.3-3.0 MHz - in broadcasting, with inductive heating of metals and other materials.
4. High frequency current, 3.0-30 MHz - in radio broadcasting, television, medicine, when welding polymers.
5. Very high frequency current, 30-300 MHz - in radio broadcasting, television, in medicine, when welding polymers.
6. Ultra-high frequency current, 0.3-3.0 GHz - in radar, in multichannel radio communications, in radio astronomy during sterilization and cooking, etc.
7. Ultra-high frequency current. 3-30 GHz
8. Extreme high frequency current, 30-300 GHz.
In this work, I will consider the factors that determine the danger of electric shock and the main causes of electrical injuries, as well as measures to prevent and prevent them.
1. Influence of electric currenton the human body
1.1 Views electric shock
Passing through the body, an electric current produces 3 types of effects : thermal, electrolytic and biological.
thermal the 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 the action is expressed in the decomposition of blood and other organic fluids, thereby causing significant violations of their physico-chemical compositions and tissue as a whole.
biological the action 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.
Distinguish two main types of damage to the body: electrical injuries and electrical shocks. Often both types of damage accompany each other. However, they are different and should be considered separately.
electrical injury- these 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. 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 and mechanical damage.
Electrical burn- 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, they differ 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 220-6000 V electrical installations, 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. As a rule, electric signs are painless and their treatment ends safely: over time, the top layer of the skin comes off and the affected area acquires its original color, elasticity and sensitivity. Signs occur quite often - in about 20% of those affected by the current.
Leather plating- penetration into the skin of the smallest particles of metal melted under the action of an electric arc. This phenomenon occurs during short circuits, disconnectors and knife switches under load, etc. The affected area of the skin has a rough, hard surface. Sometimes there is reddening of the skin caused by a burn, due to the heat brought into the skin by the metal. The victim feels skin tension on the affected area from the presence of a foreign body in it, and in some cases experiences pain from burns.
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.
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.
1.2 electric shock
electric shock- this 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:
1. convulsive muscle contraction without loss of consciousness;
2. convulsive muscle contraction with loss of consciousness, but with preserved breathing and heart function;
3. loss of consciousness and impaired cardiac activity or breathing (or both);
4. Clinical death, that is, lack of breathing and circulation.
Clinical (or “imaginary”) death is a transitional period from life to death, occurring from the moment of cessation of activity and lungs. A person who is in a state of clinical death lacks all 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. These circumstances make it possible to restore the fading or just extinct functions of the organism, that is, to revive the dying organism.
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- 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.
Cause of death from electric shock there may be a cessation of the heart, cessation of breathing and electric 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.
Cessation of breathing as the root cause of death from electric current is caused by the 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 action of the current, asphyxia can occur - asphyxiation as a result of a lack of oxygen and an excess of carbon dioxide in the body.
electric shock- 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 this, 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.
1.3 Electricalwhat is the resistance of the human body
The human body is a conductor of electric current. Different tissues of the body provide different resistance to current: skin, bones, adipose tissue - large, and muscle tissue, blood, and especially the spinal cord and brain - small. The skin has a very high resistivity, which is the main factor determining the resistance of the entire human body.
The resistance of the human body with dry, clean and intact skin (measured at voltages up to 15-20 V) ranges from about 3000 to 100,000 ohms, and sometimes more.
Usually, with alternating current of industrial frequency, only the active resistance of the human body is taken into account and taken equal to 1000 ohms. In reality, this resistance is a variable value that has a non-linear dependence on many factors, including skin condition, electrical circuit parameters, physiological factors and environmental conditions.
Skin condition- greatly affects the magnitude of the resistance of the human body. So, damage to the stratum corneum, including cuts, scratches, abrasions and other microtraumas, can reduce the total body resistance to a value close to the value of internal resistance, which certainly increases the risk of electric shock to a person. Moisturizing the skin with water or sweat, as well as contamination of the skin with conductive dust or dirt, has the same effect.
Since the skin resistance of the same person is not the same in different parts of the body, the place where the contacts are applied, as well as their area, affects the resistance as a whole. The magnitude of the current and the duration of its passage through the body have a direct effect on the total resistance: with an increase in the current and the time of its passage, the resistance decreases, since this increases the local heating of the skin, which leads to the expansion of its vessels, and consequently to an increase in the supply of blood to this area and an increase in perspiration.
1.4 Main factors, owaffecting the outcome of electric shock
The magnitude of the electric current passing through the human body is the main factor determining the outcome of the lesion. At the same time, the duration of the current exposure, its frequency, as well as some other factors are of great importance. The resistance of the human body and the amount of voltage applied to it also affect the outcome of the lesion, but only insofar as they determine the amount of current passing through the person.
A person begins to feel the effect of the current passing through him small value: 0.6-1.5 mA at alternating current with a frequency of 50 Hz and 5-7 mA at direct current. This current is called the sensible current threshold or sensible threshold current. Large currents cause muscle cramps and unpleasant painful sensations, which increase with increasing current and spread to larger areas of the body. At 10-15 mA, 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 unclench the hand in which the current-carrying part is clamped, he cannot throw the wire away from himself, etc., that is, he is not able to break contact with the current-carrying part on his own and becomes, as it were, chained to it. Larger currents produce the same effect. All these currents are called non-release currents, and the smallest of them - 10-15 mA at a frequency of 50 Hz (and 50-80 mA at direct current) is called the non-release current threshold or threshold non-release current.
A current of 25-50 mA at a frequency of 50 Hz affects the muscles not only of the arms, but also of the body, including the muscles of the chest, as a result of which breathing becomes very difficult. Prolonged exposure to this current can cause cessation of breathing, after which, after some time, death by suffocation will occur. Currents over 50 mA up to 100 mA at 50 Hz disrupt the functioning of the lungs and heart even faster. However, in this case, as with lower currents, the lungs are affected first in time and then the heart.
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 1-2 seconds from the moment the circuit of this current is closed, fibrillation can occur through a person. At the same time, blood circulation stops and a lack of oxygen occurs in the body, which, in turn, leads to the cessation of breathing, that is, death occurs. These currents are called fibrillation currents, and the smallest of them is called the threshold fibrillation current.
A current of more than 5 A, as a rule, does not cause cardiac fibrillation. With such currents immediate cardiac arrest, bypassing the state of fibrillation, as well as respiratory paralysis. If the action of the current was short-term (up to 1-2 s) and did not cause damage to the heart (as a result of heating, burns, etc.), then after the current is turned off, the heart, as a rule, resumes normal activity on its own. Breathing about this does not recover on its own and immediate assistance is required to the victim in the form of artificial respiration.
The duration of the passage of current through a living organism significantly affects the outcome of the lesion: the longer the action of the current, the greater the likelihood of a severe injury or death. This dependence is explained by the fact that with an increase in the time of current exposure to living tissue, the value of this current increases, the probability of the coincidence of the moment of passage of the current through the heart with the vulnerable phase T of the cardiac cycle (0.2 s) increases.
The current path in the body of the victim plays a significant role in the outcome of the lesion.. If vital organs - the heart, respiratory organs, brain - are in the path of the current, then the danger of injury is very high, since the current acts directly on these organs. When the current passes through other paths, the effect on the vital organs can only be a reflex, due to which the likelihood of a severe injury is sharply reduced. Since the resistance of the skin in different parts of the body is different, the influence of the current path on the outcome of the lesion also depends on the place where the current-carrying paths are applied to the body of the victim.
There are a lot of possible current paths in the human body; the most common are the following: right arm - legs, left arm - legs, arm - arm and leg - leg. The danger of one or another current path can be assessed by the severity of the lesion, as well as by the value of the current flowing through the heart, with a given loop.
It is known that the value of the current passing through the human heart (as a percentage of the total current passing through the body) is 6.7% during the path right arm - legs; left arm - legs - 3.7%; hand - hand - 3.3%; leg - leg - 0.4%.
Thus, the most dangerous path is the right hand - legs, and the least dangerous - the leg - leg path.
Direct current, as practice shows, is about 4-5 times safer than alternating current of industrial frequency (50 Hz). However, this is true for relatively small voltages - up to 250-300 V. At more high voltages the danger of direct current increases.
Individual properties of a person play a significant role in the outcome of the lesion. It has been established that healthy and physically strong people tolerate electric shocks more easily than sick and weak people. Persons suffering from a number of diseases, primarily diseases of the skin, cardiovascular system, internal secretion organs, lungs, nervous diseases, etc., have an increased susceptibility to electric current.
2. Conditionsand reasonsat which electric shock occurs
Causes of electric shock:
§ touching live parts, bare wires, contacts of electrical appliances, knife switches, lamp sockets, live fuses;
§ touching parts of electrical equipment, metal structures of structures, etc., which are not in their usual state, but as a result of damage (breakdown) of insulation that are energized:
§ being near the junction with the ground of a broken wire of the power supply network;
§ being in close proximity to live parts that are energized above 1000 V;
§ touching a live part and a wet wall or metal structure connected to the ground;
§ simultaneous contact with two wires or other live parts that are energized;
§ inconsistent and erroneous actions of personnel (powering the installation where people work; leaving the installation energized without supervision; admission to work on disconnected electrical equipment without checking for the absence of voltage, etc.).
A person falls under the influence of electric current when accidentally touching the current-carrying parts of the electrical installation or approaching an unacceptably close distance, if an emergency mode occurs in the electrical installation; in case of non-compliance of the parameters of the electrical installation with the norms, as well as in case of violation of the safety regulations and operation of electrical installations.
Table 1. Statistical data on the causes of people getting under voltage
Reason for defeat |
% of all electrical injuries |
|
Touching open live parts under voltage |
||
Touching the conductive parts of the equipment that are energized as a result of damage to the insulation |
||
Touching live parts covered with insulation that has lost its properties; touching current-carrying parts with objects with low electrical resistance |
||
Contact with floors, walls, structural elements, soil that are energized due to an emergency ground fault |
||
Defeat through an electric arc |
electric shock factor
When considering the conditions for the emergence of an electrical circuit through the human body, direct contact of a person with current-carrying parts and indirect contact are distinguished. Direct contact occurs, as a rule, as a result of a violation of safety regulations and the operation of electrical installations, and indirect contact occurs when there is a breakdown of insulation on the equipment case.
Short circuit to the body - an accidental electrical connection of the current-carrying part with metal non-current-carrying parts of the electrical installation. Earth fault - an accidental electrical connection of a current-carrying part with the earth or non-current-carrying conductive structures or objects that are not isolated from the earth.
Current passes through the human body when a person touches two points at the same time, between which there is a voltage. The magnitude of the striking current depends on which parts of the electrical installation a person touches, that is, on the conditions of the defeat.
The following lesion conditions may be observed:
bipolar contact with live parts
With a bipolar touch to current-carrying parts, a person simultaneously touches with parts of the body (for example, hands) the current-carrying parts of the equipment.
single-pole contact to live parts
The current circuit through the human body in a network with an isolated neutral closes through the ground and conduction existing between the phases of the network and the ground. In a network with a grounded neutral, the current is closed through a person, earth and neutral ground. Thus, with a unipolar touch, one of the touch points is the point of the ground (earth).
touching grounded non-current-carrying parts that are energized
When touching grounded equipment that is energized, a person is in the current spreading zone, that is, in the zone, each point of which has a certain electric potential due to the flow of ground fault current through the ground electrode.
touch voltage
In all cases of electric shock to a person, voltage is applied to the entire circuit of a person, which includes resistance: body, shoes, floor or ground on which a person stands, etc. That part of the voltage that falls on the human body in this circuit is called the touch voltage.
step voltage impact
If a person is near a grounding conductor from which current flows into the ground or near a place of an accidental short circuit to the ground, then part of this current can branch off and pass through the person’s legs. The potential difference between the feet at a step distance in the current spreading zone is called the step voltage. The step voltage is defined as the voltage between two points of the ground in the current spreading zone, located one from the other at a step distance, on which the feet of a walking person simultaneously rest. The step voltage is greater, the closer a person is to the grounding conductor and the longer the length of his step. From here, measures to prevent damage by step voltage are obvious - eliminating the possibility of people staying in the current spreading zone and removing a person from the zone in which a dangerous potential arose, in small steps.
3. Measures to ensure electrical safetyin production
3.1 Organizational safeguards
briefing
The purpose of the briefing is to provide employees with the knowledge necessary for the correct and safe performance of their professional duties.
There are the following types.
induction training
initial briefing
periodic (repeated).
Safety
Safety is a system of technical means and methods of work that ensure the safety of working conditions. This is one of the most important measures in the field of labor protection.
Proper organization of the workplace
A workplace is a zone of application of labor of a certain employee or group of workers (teams).
Mode of work and rest
The optimal mode of work and rest is such an alternation of periods of work with periods of rest, in which the greatest efficiency of human activity and a good state of health are achieved.
The optimal mode of work and rest is achieved:
pauses in work and breaks;
changing forms of work and environmental conditions;
maintaining a certain pace and rhythm of work;
elimination of monotony and inactivity;
removal of neuropsychic stress by rest in the personnel rest rooms;
using the psychological impact of color, music and technical aesthetics.
Use of personal protective equipment
Personal protective equipment is designed to protect the body, respiratory organs, vision, hearing, head, face and hands from injuries and exposure to adverse production factors.
Electrical protective equipment is divided into basic and additional ..
Main electrical protective equipment for work in electrical installations with voltage above 1 kV: insulating rods, insulating and electrical clamps, voltage indicators.
Additional: dielectric gloves, boots, carpets and caps; individual shielding kits, insulating stands and pads; portable grounding; protective devices; posters and safety signs.
Basic electrical protective equipment for work in electrical installations with voltage up to 1 kV: insulating rods, insulating and electrical pliers, voltage indicators, dielectric gloves, bench and assembly tools with insulating handles.
Additional: dielectric galoshes and carpets, portable grounding, insulating stands and pads, protective devices, posters and safety signs.
Use of warning posters and safety signs
When working in electrical installations, there is a risk of loss of orientation by workers.
Recruitment
Safety regulations provide for the selection of personnel for the maintenance of existing electrical installations for health reasons.
3.2 Organizational and technical protection measures
Insulation and fencing of live parts of electrical equipment
To exclude the possibility of touching or dangerously approaching uninsulated live parts, the inaccessibility of the latter must be ensured by fencing or locating live parts at an inaccessible height or in an inaccessible place.
Applying locks
Interlocks are used to ensure that bare live parts are inaccessible. They are used in electrical installations in which work is often carried out on protected current-carrying parts (test benches, installations for testing insulation with increased voltage, etc.).
Portable earthing switches
These are temporary grounding switches that are designed to protect against electric shock to personnel working on disconnected current-carrying parts of an electrical installation, in case of accidental voltage on these parts.
Protective isolation
Ш working - electrical insulation of the current-carrying parts of the electrical installation, ensuring its normal operation and protection against electric shock;
Ш additional - electrical insulation provided in addition to the working insulation to protect against electric shock in case of damage to the working insulation;
Ш double - electrical insulation, consisting of working and additional insulation.
Workplace isolation.
Conclusion
Perhaps there is no such professional activity where electric current would not be used. Even a teacher often resorts to electrical appliances (tape recorder, projector, lighting lamps) - what can we say about other professions.
In addition, it should be noted a serious danger to human health, which is an electric current. Its effect on the body, which is a conductor with a resistance of about 1000 ohms, is manifested by contact (often accidental) of any part of his body with live components of the electrical circuit. This effect directly depends on the characteristics of the current (strength and voltage) in the circuit, as well as on the physical and neuropsychic state of a person.
With an electric shock, we can talk about the severity of the damaging current: safe releasing, irritating, non-releasing and deadly currents.
In addition to touching the live parts of the equipment or bare wires, the cause of electric shock can be the so-called step voltage.
The most terrible 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.
List of used literature
1. V.E. Anofrikov, S.A. Bobok, M.N. Dudko, G.D. Elistratov Life Safety: Textbook for High Schools, SUM. Moscow, CJSC “Finstatinform”, 1999. 156p.
2. Ed. B.A. Knyazevsky Occupational safety. Moscow, Higher School, 1972., 67p.
3. V.I.Rusin, G.G.Orlov, N.M.Nedelko et al. Occupational safety in construction. Engineering solutions: Handbook, Kyiv, "Budivelnyk", 1990, 45p.
4. Ed. B.A. Knyazevsky Occupational safety in the energy sector, Moscow, Energoatomizdat, 1985, 200pp.
5. Under the total. ed. I.S. Ivanova Countries of the World: A Handbook, Moscow, Respublika, 1999, 143 pp.
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The nature and consequences of human exposure to electric current depend on the following factors:
The value of the current passing through the human body,
human electrical resistance,
The level of stress applied to a person,
Duration of exposure to electric current,
Current paths through the human body
Type and frequency of electric current,
environmental conditions and other factors.
Electrical resistance of the human body.
The human body is a conductor of electric current, however, inhomogeneous in electrical resistance. 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 skin is made up of two main layers: the outer layer, the epidermis, and the inner layer, the dermis. The outer layer - the epidermis, in turn, has several layers, of which the thickest upper layer is called the stratum corneum. The stratum corneum in a dry, uncontaminated state can be considered as a dielectric: its volume resistivity reaches 10 5 - 10 6 Ohm m, which is thousands of times higher than the resistance of other skin layers, the resistance of the dermis is insignificant: it is many times less than the resistance of the stratum corneum.
The resistance of the human body with dry, clean and intact skin (measured at a voltage of 15-20 V) ranges from 3 to 100 kOhm or more, and the resistance of the inner layers of the body is only 300-500 Ohm.
As a calculated value for alternating current of industrial frequency, the resistance of the human body is used, equal to 1000 ohms.
Under actual conditions, the resistance of the human body is not a constant value. It depends on a number of factors, including the condition of the skin, the state of the environment, the parameters of the electrical circuit, etc.
Damage to the stratum corneum (cuts, scratches, abrasions, etc.) reduces the resistance of the body to 500-700 ohms, which increases the risk of electric shock to a person. Moisturizing the skin with water or sweat has the same effect.
Contamination of the skin with harmful substances that conduct electric current well (dust, scale, etc.) leads to a decrease in its resistance.
The resistance of the body is also influenced by the area of contacts, as well as the place of contact, since in the same person the resistance of the skin is not the same in different parts of the body. The skin of the face, neck, hands in the area above the palms has the least resistance, and especially on the side facing the torso, armpits, back of the hand, etc. The skin of the palms and soles has a resistance that is many times greater than the resistance of the skin of other parts of the body.
With an increase in the current and the time of its passage, the resistance of the human body decreases, since this increases the local heating of the skin, which leads to the expansion of its vessels, to an increase in the supply of this area with blood and an increase in sweating.
With an increase in the voltage applied to the human body, the skin resistance decreases tenfold, approaching the resistance of internal tissues (300-500 ohms). This is due to an electrical breakdown of the stratum corneum of the skin, an increase in the current passing through the skin.
With an increase in the current frequency, the resistance of the body will decrease, and at 10-20 kHz, the outer layer of the skin practically loses its resistance to electric current.
The magnitude of the current. The main factor that determines the outcome of an electric shock is the strength of the current passing through the human body. The nature of the impact of current on a person, depending on the strength and type of current, is given in Table 7.1
Table 7.1.
The nature of the impact of current on a person (current path arm - leg, voltage 220 V)
AC, 50 Hz |
direct current |
|
The beginning of the sensation, slight trembling of the fingers |
No sensations |
|
The beginning of pain |
No sensations |
|
The beginning of cramps in the hands |
Itching, feeling of warmth |
|
Cramps in the hands, it is difficult, but you can break away from the electrodes |
Increased feeling of warmth |
|
Severe cramps and pain, persistent current, difficulty breathing | ||
Respiratory paralysis |
Hand cramps, difficulty breathing |
|
Respiratory paralysis with prolonged current flow |
||
Same, less time |
Cardiac fibrillation under the action of current for 2-3 s, respiratory paralysis |
Perceptible current is an electric current that causes perceptible irritations when passing through the body. Perceptible irritations are caused by an alternating current of 0.6-1.5 A and a constant current of 5-7 A. The indicated values \u200b\u200bare threshold perceptible currents; the region of perceptible currents begins with them.
Continuous current- an electric current that, when passing through a person, causes irresistible convulsive contractions of the muscles of the hand in which the conductor is clamped. The threshold hold current is 10-15mA AC and 50-60mA DC. With such a current, a person can no longer independently open his hand, in which the current-carrying part is clamped and turns out to be, as it were, chained to it.
fibrillation current- an electric current that causes fibrillation of the heart when passing through the body. The threshold fibrillation current is 100 mA AC and 300 mA DC with an exposure duration of 1-2 s. along the way hand-foot or hand-hand. The fibrillation current can reach 5A. A current greater than 5A does not cause cardiac fibrillation. With such currents, instantaneous cardiac arrest occurs.
Duration of exposure to electric current . The duration of the passage of current through the human body has a significant impact on the outcome of the lesion. The danger of electric shock due to cardiac fibrillation depends on which phase of the cardiac cycle coincides with the time of passage of current through the region of the heart. If the duration of current passage is equal to or exceeds the cardiocycle time (0.75-1s), then the current "meets" with all phases of the heart (including the most vulnerable), which is very dangerous for the body. If the time of current exposure is less than the duration of the cardiocycle by 0.5 s or more, then the probability of the coincidence of the moment of passage of the current with the most vulnerable phase of the heart, and, consequently, the risk of damage is sharply reduced. This circumstance is used in high-speed residual current devices, where the response time is less than 0.2 s.
The path of current through the human body. It plays a significant role in the outcome of the lesion, since the current can pass through vital organs: the heart, lungs, brain, etc. The influence of the current path on the outcome of the lesion is also determined by the resistance of the skin in various parts of the body.
There are a lot of possible current paths in the human body, which are also called current loops. The most common current loops are: arm-arm, arm-leg, leg-leg. The most dangerous are head-arm and head-leg loops.
Type and frequency of electric current . Direct current is about 4-5 times safer than alternating current. This provision is valid only for voltages up to 250-300V. At higher voltages, direct current is more dangerous than alternating current (with a frequency of 50 Hz).
With an increase in the frequency of the alternating current, the impedance of the body decreases, which leads to an increase in the current passing through the person, therefore, the danger of injury increases.
Conditions of the external environment. Dampness, conductive dust, caustic vapors and gases that destroy the insulation of electrical installations, as well as high ambient temperature, lower the electrical resistance of the human body, which further increases the risk of electric shock.
Depending on the presence of the listed conditions that increase the risk of electric shock to a person, all rooms are divided according to the risk of electric shock to a person into the following classes: (Table 7.2.)
Table 7.2.
Classification of premises according to the danger of electric shock
Electric current safety criteria. When designing, calculating and operating control of protective systems, they are guided by the permissible values of the current for a given path of its flow and the duration of exposure in accordance with GOST 12.1.038-82.
With prolonged exposure, the allowable current is assumed to be 1 mA. With exposure duration up to 30 s - 6 mA. When exposed to 1 s or less, the values of the currents are given in Table 7.3. However, they cannot be considered as providing complete safety, and are accepted as practically acceptable with a fairly low probability of damage.
Table 7.3.
Practically admissible current values
These currents are considered acceptable for the most probable paths of their flow in the human body: hand-hand, hand-foot, and foot-foot.
The nature and consequences of the impact of an electric current on a person are determined by the electrical resistance of the human body, the voltage of the current and the duration of the impact of the electric current, depend on the direction of the passage of current through the human body, the type and frequency of the electric current, and also on environmental conditions.
Electrical resistance of the human body. The human body is a conductor of electric current, however, inhomogeneous in electrical resistance. The greatest resistance to electric current is provided by the skin, therefore the total resistance of the human body is determined mainly by the value of the resistance of the skin. The skin consists of two main layers: the outer - the epidermis - and the inner - the dermis.
The outer layer - in turn, has several layers, of which the thickest upper layer is called the horny.
The stratum corneum in a dry, uncontaminated state can be considered as a dielectric. Its specific volume resistance reaches 105-106 Ohm m, thousands of times higher than the resistance of other layers of the skin (dermis) and internal tissues of the body.
The resistance of the human body with dry clean and intact skin (measured at a voltage of 15-20 V) ranges from 3 to 100 kOhm or more, and the resistance of the inner layers of the body is only 300-500 Ohm.
For calculations, the value of the resistance of the human body is taken equal to 1000 ohms.
In reality, the resistance of the human body is not constant. It depends on the condition of the skin, the environment, the parameters of the electrical circuit, etc.
Damage to the stratum corneum (cuts, scratches, abrasions) reduces the resistance of the body to 500 - 700 ohms, which increases the risk of electric shock to a person.
Moisturizing the skin with water or sweat has the same effect. Therefore, working with electrical installations with wet hands and in conditions that cause skin moisture, as well as at elevated temperatures, exacerbates the risk of electric shock to a person.
Contamination of the skin with harmful substances that conduct electric current well (dust, scale) also leads to a decrease in its resistance.
The area 1b of contact and the place of contact are important, since the resistance of the skin is not the same in different parts of the body. The skin of the face, neck, palms and arms has the least resistance, especially on the side facing the torso (armpits, etc.). The skin of the back of the hand and soles has a resistance many times greater than the resistance of the skin of other parts of the body.
Current strength and voltage. The main factor determining the outcome of an electric shock to a person is the strength of the current passing through his body (Table 20.1). With an increase in the current strength, the resistance of the human body decreases, as the local heating of the skin increases, which leads to the expansion of blood vessels, an increase in the supply of blood to this area and an increase in sweating.
The voltage applied to the human gel also affects the outcome of the lesion, since it determines the value of the current passing through the person.
Table 20.1. Threshold values for different types of current
* Instantaneous cardiac arrest occurs at a current strength of 5 A.
times, approaching the resistance of internal tissues (300 - 500 ohms), increase the current strength accordingly.
Type and frequency of electric current. Direct current is about 4 to 5 times safer than alternating current. This follows from a comparison of the threshold values of perceptible and non-releasing direct and alternating currents. But this is true only up to voltages of 250 - 300 V. At higher voltages, direct current becomes more dangerous than alternating current (with a frequency of 50 Hz).
With regard to alternating current, its frequency is important. With an increase in the frequency of alternating current, the impedance of the body decreases and at 10 - 20 kHz the outer layer of the skin practically loses resistance to electric current, which also leads to an increase in the current passing through the person, and therefore, the risk of injury increases.
The greatest danger is the current with a frequency of 50 to 1000 Hz. With a further increase in frequency, the danger of damage decreases and completely disappears at a frequency of 45 - 50 kHz. These currents are dangerous only from the point of view of burns. The decrease in the risk of electric shock with increasing frequency becomes practically noticeable at 1-2 kHz.
Duration of exposure to electric current. Prolonged exposure to electric current leads to severe and sometimes fatal injuries to a person.
A long-term exposure to a current of 1 mA is considered safe, with a duration of up to 30 s, a current of 6 mA is safe.
Practically acceptable with a fairly low probability of damage, the following values \u200b\u200bof the current strength are accepted:
Duration of exposure, s Current, mA
1,0 50 7 70
0,5 100
0,2 250
The path of current through the human body. This factor also plays a significant role in the outcome of the lesion, since the current can pass through vital organs - the heart, lungs, brain, etc.
There are quite a lot of possible paths for the passage of current through the human body, which are also called current loops. The most common current loops - arm - arm, arm - legs and leg - leg - are presented in Table. 20.2.
The most dangerous are those that can affect the area of \u200b\u200bthe heart, that is, the head - arms and head - legs. But they are relatively rare.
Table 20.2. Characteristics of current passage paths through the human body, %
Individual properties of a person. It has been established that physically healthy and strong people endure electric shocks more easily.
Persons suffering from skin diseases, diseases of the cardiovascular system, organs of internal secretion and lungs, nervous diseases, etc., are distinguished by increased susceptibility to electric current.
The safety rules for the operation of electrical installations provide for the selection of personnel for the maintenance of existing electrical installations, based on the state of health of people. For this purpose, a medical examination of persons is carried out upon their admission to work, which is periodically repeated once every two years, taking into account the list of diseases and disorders that are a contraindication to the maintenance of existing electrical installations.
Conditions of the external environment. The state of the surrounding air, as well as the surrounding environment, can significantly affect the risk of electric shock.
Dampness, conductive dust, the presence of caustic vapors and gases that destroy the insulation of electrical installations, as well as high ambient temperature, reduce the electrical resistance of the human body, which further increases the risk of electric shock.
The impact of current on a person is also exacerbated by conductive floors and metal structures close to the electrical equipment that have a connection with the ground, since when this object and the body of electrical equipment that accidentally become energized are touched at the same time, a gok of great force will pass through the person.
Depending on the listed conditions that increase the risk of electric shock to a person, the "Electrical Installation Rules" divide all premises into four classes according to the danger of electric shock to people. Premises without increased danger. They are characterized by the absence of conditions that create an increased or special danger (clauses 2 and 3). High risk areas. Are characterized by the presence of one of the following conditions:
a) dampness (when the relative humidity of the air exceeds 75% for a long time) or conductive dust;
b) conductive floors (metal, earthen, reinforced concrete, brick, etc.);
c) high temperature (above 35 °C);
d) 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. Particularly dangerous premises. Are characterized by the presence of one of the following conditions:
a) special dampness (at a relative air humidity close to 100%, when the ceiling, walls, floor and objects in the room are covered with moisture);
b) chemically active or organic environment that destroys the insulation and current-carrying parts of electrical equipment;
c) the presence of two or more conditions of increased danger at the same time (clause 2). Territories for placement of outdoor electrical installations. According to the danger of electric shock to people, these territories are equated to especially dangerous premises.
In the chemical industry, many production facilities are particularly dangerous.
In addition, depending on the climatic environment, the premises are divided into: dry (normal) with humidity up to 60%, wet (60 - 75%), damp (more than 75%), especially damp (with humidity close to 100%), hot (at a constant temperature above 35 ° C), dusty, rooms with a chemically active or organic environment.
Electrical equipment should be selected taking into account the state of the environment and the class of the room for the danger of electric shock in order to ensure the necessary degree of safety for people during its maintenance.
Thus, electrical equipment installed in damp, especially damp and dusty rooms, as well as in rooms with a chemically active environment, must be of a closed type, have an appropriate design: drip- or splash-proof, dust-proof, ventilated. In addition, the materials from which electrical equipment is made must be corrosion-resistant, and metal parts must be reliably protected by paint and varnish or galvanized coating.
Electrical equipment and electrical networks located in rooms with a chemically active environment, as well as the places for their laying, should be selected taking into account the design and coating that ensures their protection from the effects of an aggressive environment.
In explosive areas "of all classes with chemically active environments, wires and cables with PVC insulation are used, as well as wires with rubber and cables with rubber and paper insulation in a lead or PVC sheath. The use of wires and cables with polyethylene insulation in any sheaths and coatings is prohibited.
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.
These are pronounced local (local) damage to body tissues caused by exposure to electric current or an electric arc. Local damage most often affects the surface of human skin, but in some cases, muscle tissue, as well as ligaments and bones, are also affected. Usually, local electrical injuries are cured and a person's working capacity is fully or partially restored. However, in some cases, local electrical injuries lead to the death of a person. Local electrical injuries include:
electric burns,
electrical signs (current tags),
skin electroplating,
· mechanical damage,
· electrophthalmia.
An electric shock is the effect of an electric current on a human or animal body, as a result of which a convulsive contraction of the muscles of the body begins. Depending on the magnitude of the current strength and the exposure time, the biological object may or may not be conscious, but with the independent functioning of the respiratory organs and the cardiovascular system. In the most severe conditions, after an electric shock, not only loss of consciousness is observed, but also problems in the functioning of the cardiovascular system, and even death.
23. The sequence and content of first aid measures. Ways to free the victim from the effects of electric current, personal safety measures. Features of defeat by atmospheric electricity (lightning) during lightning discharges, first aid.
First aid in case of electric shock consists in immediately turning off the electrical installation or interrupting the circuit of exposure to electric current on a person in absolutely any way possible, then, depending on the degree of damage, will begin to perform a closed heart massage and organize artificial respiration if the victim has a cardiac arrest, as well as processing and bandaging the affected parts of the body.
In case of electric shock, it is necessary to free the victim from its effects as soon as possible, since the severity of the electrical injury depends on the duration of this action.
If the victim holds the wire with his hands, his fingers are strongly compressed and it is impossible to release the wire, then the first action of the person providing assistance is to turn off the electrical installation that the victim touches. Disconnection is carried out using switches, a knife switch or other disconnecting device, as well as by removing or unscrewing the fuses (plugs), the plug connector.
With the shutdown of the electrical installation, artificial lighting can go out at the same time, so you need to take care of this by turning on emergency lighting, etc.
In this case, it is necessary to take into account the explosion and fire hazard of the room. When assisting the victim, one should not touch him without taking precautions, as this is life-threatening; care must be taken not to be in contact with the current-carrying part and under step voltage.
To separate the victim from current-carrying parts or wires with voltage up to 1,000 V, it is necessary to use a rope, stick, board or other dry object that does not conduct electric current.
If the clothes are dry and lag behind the body, then you can pull the victim away from live parts, avoiding contact (touching) with parts of the body, by the floors of a coat or jacket, jacket, by the collar.
To isolate hands, the assisting person must wear dielectric gloves or wrap a hand with a scarf, put a cloth cap on his hand, or pull the sleeve of a jacket or coat over his hand. You can isolate yourself by using a rubber mat, a dry board, or other improvised items that do not conduct electricity (bedding, a bundle of clothes).
If an electric current passes into the ground through the victim, and he convulsively squeezes the wire in his hand, then you can separate the person from the ground by slipping a dry board under him or pulling him by his clothes. You can also cut the wire with an ax with a dry wooden handle or other tools with insulated handles (pliers, etc.).
After the release of the victim from the action of electric current, it is necessary to assess his condition.
If the victim has no consciousness, breathing, pulse, the skin is cyanotic, and the pupils are wide (0.5 cm in diameter), then he is in a state of clinical death and you should immediately begin to revive the body using artificial respiration using the mouth-to-mouth method. or "mouth to nose" and external heart massage.
Having begun to revive the victim, it is necessary to take care of calling for medical help.
The same pathological changes are noted in the body of victims of atmospheric electricity damage as in case of electric shock. The victim loses consciousness, falls, convulsions may occur, breathing and heartbeat often stop. On the body, you can usually find "current marks", the points of entry and exit of electricity. In the event of a fatal outcome, the cause of the cessation of basic vital functions is a sudden cessation of breathing and heartbeat, from the direct action of lightning on the respiratory and vasomotor centers of the medulla oblongata. The victim of a lightning strike needs hospitalization, as he is at risk of disorders of the electrical activity of the heart.
In case of a lightning strike, the same assistance is provided as in case of electric shock.
A person struck by lightning is immediately given artificial respiration, in case of cardiac arrest - his closed massage and warm the body. Inside give caffeine, analgin. If possible, anti-shock agents are administered subcutaneously: promedol, caffeine, ephedrine. After restoring breathing, the victim should be given hot tea to drink, burns should be treated and transported to the hospital.
24. Flame burns, the sequence and content of first aid measures. Frostbite, first aid measures (by stages).
Burn – tissue damage caused by exposure to high temperature, chemicals, electric current, ionizing radiation. Depending on the cause of occurrence, thermal, chemical, electrical, radiation burns are distinguished. Sunburns are possible. Thermal burns are the most common.
Thermal burns. During fires, several damaging factors act on the human body. The most dangerous of them is the high temperature in the combustion zone, leading to heat stroke, burns to the skin and upper respiratory tract. Flame burns are much more severe than boiling liquid burns.. Among thermal burns of various localization, the most dangerous are burns of the face, they are accompanied by burns of the upper respiratory tract hot air.
The severity of the victim's condition depends on the degree of burn, its area and localization. The degree of burn is determined by the depth of damage to the skin and underlying tissues. Allocate IV degree burns.
1st degree burn manifested by redness of the skin, swelling, pain.
Second degree burn characterized by the formation of blisters filled with a clear yellowish liquid, a sharp reddening of the skin, burning pain.
Third degree burn accompanied by necrosis of all layers of the skin. The surface of the burn is covered with a scab - a dense gray-brown crust. In connection with the defeat of the nerve endings, the pain is insignificant or absent. Dead tissue suppurates and is torn away. Healing is slow. A scar forms at the site of the burn.
IV degree burn characterized by charring of the skin, subcutaneous fat, muscles and even bones. Pain sensitivity is lost. Skin grafting is needed to heal deep burns.
Determining the area of the burn
The area of the burn is determined by the "rule of nines". The surface of the head and neck is 9% of the body surface of an adult, one upper limb - 9%, one lower limb - 18% (thigh - 9%, lower leg and foot - 9%). The back surface of the human torso is 18% of the body surface, the front surface (chest, abdomen) - 18%, the perineum and external genitalia - 1%.
The area of the burn can also be determined by the “rule of the palm”. The area of the palm of the victim is 1% of the surface of his body. The palm is projected over the affected area, without touching the burned area of the body.
Burns over 15% of the body surface in adults are accompanied by burn shock. In children, burn shock develops when the burn area is 5–10% or more. There are 2 phases of burn shock: the first is the excitation phase, the second is inhibition. The first phase is short. The victims are excited, restless due to the continuous flow of pain impulses from burn wounds. The second phase is characterized by a pronounced inhibition of the activity of the nervous system, heart, lungs, kidneys and other organs. The indifferent look of the victims is noteworthy. Danger to life arises even with second-degree burns, occupying ⅓ of the body surface.
With extensive burns, toxic substances are formed in the affected areas. Penetrating into the blood, they are carried throughout the body and cause intoxication. Microorganisms get on the burned areas of the skin, burn wounds begin to suppurate. Burn disease develops. The deeper the damage to the skin and underlying tissues and the larger the area of the burn, the more severe the condition of the victim and the worse the prognosis.
Frostbite is damage to body tissues caused by cold. Frostbite is more susceptible to fingers and toes, nose, ears and face. The severity of frostbite depends on the duration of exposure to cold, as well as on the state of the body.
With alcohol intoxication, the thermoregulation of the body is disturbed, and the likelihood of frostbite increases! Sign: a sharp blanching of the skin and loss of its sensitivity. The main task of first aid is to stop exposure to cold and restore the normal temperature of the cooled tissues as quickly as possible. For this you need:
immerse frostbitten parts of the body in water with a temperature of 37 ° C to 40 ° C, but not higher due to the risk of burns;
make a light rubbing of frostbitten skin.
It is forbidden to rub frostbitten areas with snow or immerse them in cold water, as this causes further hypothermia!
Sterile dressings are applied to frostbitten skin to prevent infection. If pain, swelling of tissues, blisters appear, you should seek medical help.