Chapter 14. Human protective equipment

FROM ELECTRIC CURRENT

ELECTRIC SHOCK HAZARD

The effect of electric current on the human body. Electric current is currently used in all areas of human activity: production, everyday life, medicine, etc., as an energy source that is convenient to transport and use. With all the benefits of using electricity, the dangers of electricity to humans cannot be ignored.

The effect of electric current on living tissue, unlike other factors, is unique and versatile. Passing through the body, electric current produces thermal, electrolytic, mechanical (dynamic) and biological effects.

Thermal action manifests itself in the heating of tissues up to burns of individual parts of the body, heating to a high temperature of blood vessels, nerves, heart, brain and other organs located in the path of the current, which causes serious functional disorders in them.

Electrolytic action causes decomposition of blood and plasma, which is accompanied by significant disturbances in their physical chemical composition.

Mechanical (dynamic) action current is expressed in stratification, rupture and other similar damage to various tissues of the body: muscle tissue, walls of blood vessels, vessels of pulmonary tissue.

Biological effect is expressed in irritation and excitation of living tissues of the body, which can be accompanied by involuntary convulsive contractions of muscles, including the muscles of the heart and lungs, as well as disruption of internal bioelectric processes that occur in a normally functioning body and are closely related to its vital functions.

These actions are conventionally reduced to two main types of injuries: local electrical injuries and electrical shocks

Local electrical injuries - These are clearly defined local violations of the integrity of body tissues caused by exposure to electric current or electric arc. Characteristic species local electrical injuries - electrical burns, electrical marks and marks, skin metallization, electroophthalmia and mechanical damage.

Electric shock - This is the stimulation of living tissues of the body by an electric current passing through it. It can cause convulsive muscle contractions without loss of consciousness, with loss of consciousness, without or with damage to the heart and respiratory system, as well as clinical death. Clinical, or imaginary, death - a short-term transitional state from life to death, occurring from the moment the activity of the heart and lungs ceases. Signs clinical death the following: cardiac arrest and, as a result, absence of a pulse, lack of breathing, the skin is bluish-pale, the pupils of the eyes are sharply dilated (due to oxygen starvation of the cerebral cortex) and do not react to light, painful stimuli do not cause any reactions in the victim. The duration of clinical death is determined by the time from the moment of cessation of cardiac activity and respiration until the beginning of the death of cells in the cerebral cortex; in most cases it is 4 - 5 minutes.

Factors determining the outcome of electric shock. In general, the degree of electric shock is determined by the amount of electrical energy absorbed in organs, tissues and systems when an electrical circuit occurs through the human body.

The nature of the impact and the severity of the injury to a person depends on many interrelated factors, such as the strength of the current, the duration of exposure to the current, the resistance of the human body, the path of passage, the type (constant, straightened, alternating) and frequency of the current, the “attention factor”, the individual properties of the victim and factors environment.

With increase amperage Three qualitatively different responses of the body are clearly manifested: an unpleasant sensation, convulsive muscle contraction and cardiac fibrillation. Electric currents that cause a corresponding reaction are divided into tangible, non-releasing and fibrillation, and their minimum values ​​are usually called threshold.

As shown experimental studies, the person begins to feel the flow through him alternating current frequency 50 Hz with a force of about 0.6 - 1.5 mA. A noticeable current does not cause disturbances in the body’s functioning, so its long-term flow through the human body under industrial conditions is permissible.

If a person who has come under voltage is able to independently overcome the effect of the convulsion and free himself from contact with the conductors, then such a current is called releasing current. In cases where a person cannot independently free himself from contact, there is a danger of prolonged convulsions. The currents that cause such a reaction in the body are called non-releasing currents. Threshold values ​​of non-releasing alternating currents at a frequency of 50 Hz lie within 10 - 15 mA. At 25–50 mA, the effect of the current extends to the muscles of the chest, which leads to difficulty and even cessation of breathing. When exposed to this current, death can occur within a few minutes due to the cessation of lung function. There is a dependence of threshold non-releasing currents on a person’s weight and age. Thus, with an increase in weight from 50 to 80 kg, the threshold current value increases by 1.4 - 2 times.

A current of 50–80 mA affects the respiratory system and cardiovascular system. At 100 mA, cardiac fibrillation occurs within 2–3 seconds, consisting of random chaotic contraction and relaxation of the cardiac muscle fibers (fibrils). It stops, blood circulation stops. This current is called fibrillation current.

Duration of current flow through the human body affects the resistance of the skin, as a result of which, with increasing time of exposure to current on living tissue, its value increases, and the consequences of the influence of current on the body increase.

Currents permissible for humans are assessed according to three electrical safety criteria. First criterion - a tangible current that does not cause disturbances in the body’s functioning and is allowed to flow for a long time (no more than 10 minutes per day) through the human body in normal (non-emergency) mode of the electrical installation. For alternating current with a frequency of 50 Hz its strength is 0.3 mA, and for direct current - 1 mA. The releasing current is taken as the second criterion. Its effect on a person is permissible for a duration of more than 1 second. The releasing current for alternating current is 6 mA, for direct current - 15 mA. The third criterion is a fibrillation current that does not exceed the threshold fibrillation current and acts for a short time (up to 1 s). The maximum permissible values ​​of alternating currents with a frequency of 50 Hz and touch voltages during emergency operation of industrial electrical installations with voltages up to 1000 V, depending on the duration of exposure, should not exceed the values ​​​​specified in GOST 12.1.038-82 as amended. dated 07/01/88 and shown in table 14.1.

Table 14.1

Maximum permissible values ​​of touch voltage U etc. and currents Ih,

flowing through the human body, in emergency mode

industrial electrical installations with voltage up to 1000 V

Knowledge of the standards for permissible values ​​of touch voltages and currents through the human body is necessary when developing methods and means of protecting people, when assessing electrical safety conditions in existing electrical installations, and when investigating electrical injuries.

Electrical resistance of the human body is variable, depending on touch voltage, skin condition, electrical circuit parameters, physiological factors and environmental conditions.

The total electrical resistance of the human body has active and capacitive components and consists of the resistance of the skin and the resistance of internal tissues.

The top layer of skin, called the epidermis, which consists mainly of dead keratinized cells, has a large resistance that determines the overall resistance of the human body. The resistance of the lower layers (dermis) and internal human tissues is insignificant (300–500 Ohms). With dry, clean and undamaged skin, the resistance of the human body, measured at voltages up to 15–20 V, ranges from (3–100) × 10 3 Ohms. When moistened, as well as when it is damaged (under the contacts), the body resistance turns out to be the smallest - about 500 Ohms, i.e. reaches a value equal to the resistance of the internal tissues of the body. For approximate calculations, the resistance of the human body is considered purely active and equal to 1 kOhm at touch voltages above 50 V, 6 kOhm at touch voltages less than 50 V.

Inclusion of vital human organs within the current coverage area increases the possibility of a serious outcome. The most dangerous are loops when the brain and spinal cord are in the current circuit. Death is possible even at low voltages (12 V) if the current passes through biologically active points of the body on the neck, temples, lower legs, shoulders, back and other places of the human body.

At voltages up to 500 V, alternating current is more dangerous; with a further increase in voltage, the danger of direct current quickly increases.

When the alternating current frequency changes from zero to 100 Hz, the risk of injury at the same voltage increases, reaching a maximum in the range of 50 - 60 Hz, at a frequency of 200 Hz the risk of fibrillation is reduced by 2 times, at a frequency of 400 Hz - more than 3 times.

Currents above 500,000 Hz do not cause electric shock, but they can cause thermal burns.

The physical and psychological state of a person has a certain influence on the outcome of the lesion. Fatigue, depressed mental state, alcohol consumption, and a number of diseases increase the danger of exposure to electric current. Therefore, a list of diseases has been determined, in the presence of which work in existing electrical installations is not allowed. Maintenance of electrical installations is entrusted to workers who have undergone a medical examination and special training. Great importance has an “attention factor” that reduces the danger of current.

People indoors are usually less at risk. However, if this is a production room, then the presence of dampness, conductive dust, many types of electrical equipment, aggressive environment increases the risk of electric shock.

Classification of premises according to the danger of electric shock. In accordance with the Rules for the Construction of Electrical Installations (PUE), all premises with regard to the danger of electric shock to people are divided into three classes: without increased danger, with increased danger, and especially dangerous.

Premises without increased danger - These are dry, dust-free rooms with normal air temperature and with insulating (for example, wooden) floors, i.e. in which there are no conditions that create increased or special danger. Such premises include office premises, tool storerooms, laboratories, etc.

Premises with increased danger, characterized by the presence in them of one of the following conditions that create an increased danger: dampness (relative humidity exceeds 75% for a long time) or conductive dust (coal, metal, etc.); conductive floors (metal, earthen, reinforced concrete, brick, etc.); high temperature (air temperature above +35 C); the possibility of simultaneous human touch to metal structures of buildings, technological devices, mechanisms, etc. connected to the ground, on the one hand, and to metal housings of electrical equipment - with another.

Examples of high-risk areas include stairwells in buildings with conductive floors, unheated warehouse spaces, etc.

Particularly dangerous premises, characterized by the presence of one of the following conditions that create a special danger: special dampness (relative air humidity is close to 100%); chemically active or organic environment that destroys insulation and live parts of electrical equipment; two or more high-risk conditions at the same time.

Particularly dangerous premises are most industrial premises, including all equipment repair shops, workshops, etc.

In terms of the danger of electric shock to people, the areas where outdoor electrical installations are located (in the open air or under a canopy) are equated to especially dangerous premises

In everyday life and at work, we come across various electrical appliances and electrical installations. By following electrical safety rules and having knowledge in this area, you can reduce the likelihood of being exposed to dangerous electric current and voltage.

This issue combines engineering and medical knowledge, the use of which in combination will increase the result in reducing the level of electrical injuries at home and at work.

The effect of electric current on the human body

Current, unlike other hazardous media, is colorless, odorless, and invisible.

Electric current has the following types of effects on the human body: thermal, electrolytic, biological. Let's look at each of these impacts in more detail.

The thermal effect consists of burns to areas of the body, heating of blood vessels and nerve endings. This type of action is also called thermal. Because thermal energy obtained from electrical energy creates burns.

Electrolytic exposure leads to the decomposition of blood and other fluids in the body through the process of electrolysis, which causes disturbances in the physico-chemical composition of these fluids. The essence of the damage comes down to molecular level– blood thickening, changes in protein charge, steam and gas formation in the body.

The biological effect of electric current on the body is accompanied by irritation and excitation of organs. This causes spasms and contractions.

In the case of the heart and lungs, this effect can be fatal due to the cessation of respiratory and cardiac function.

Biological effects cause mechanical damage to human organs and joints. Mechanical damage can also be caused by a person falling from a height due to exposure to electric current.

Dangerous, safe and lethal current for humans

Any amount of current cannot be considered safe for humans. There is only a more or less dangerous amount of electric current. Each person has internal resistance, the value of which is influenced by many factors (the thickness of the skin, the humidity of the room and the human body, the path of current flow).

The most dangerous path of current flow is the direction leg-head, arm-head, since in this case the path goes through the heart, brain, and respiratory organs. A large amount of current can cause cardiac arrest and respiratory arrest. These reasons are the most likely causes of death when electric current flows.

It is believed that direct current is safer than alternating current in networks up to 500. Above 500 volts, the danger of direct current increases.

The frequency of the network affects the severity of electrical injury. An industrial frequency of 50 Hz is more dangerous than a frequency of 500 Hz. At high frequencies, the so-called “skin effect” is observed, when the current does not pass through the entire conductor, but only along its surface. This means that internal organs are not directly affected.

Also, the degree of danger of exposure to current on a person is influenced by the duration of the person’s exposure to the current. Here the relationship is linear - the longer, the more destruction and adverse consequences.

Here are the threshold values ​​of alternating and direct current and possible reactions of the body to these effects:

As current passes through the human body, it can create electrical injuries or shocks.

An electric shock involves the current stimulating the tissues of the body, causing them to contract and spasm. There are 4 groups of electric shocks: convulsions, convulsions with loss of consciousness, loss of consciousness with impaired breathing and heart function, clinical death.

During an electrical injury, the current causes direct damage to human tissues and organs. These may include electrical burns, metallization of the skin, electrical marks and mechanical damage.

Electrical burns can be either electric or arc. The effect of an electric burn is associated with the passage of current through the human body. An arc burn occurs between a person and a high voltage electrical conductor due to the occurrence between them. The temperature of the arc can reach thousands of degrees Celsius. Such a burn is much more dangerous and can, in addition, be accompanied by a fire in the victim’s clothing.

Metallization of the skin occurs when metal particles enter the skin under the influence of current, and the conductivity of the skin increases, which increases the risk of injury.

Electrical marks are places through which current enters and exits the human body. Most often found on the legs and arms.

In any case, you should try to avoid touching live parts with conductive objects (fishing under power lines, carrying a stepladder near voltage bars), not using wires and cables with weakened insulation, and following safety rules when staying and working in electrical installations. Take care of the health of yourself and your family.

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Electricity is a powerful and dangerous element. She faithfully serves a person, however, if you are careless or as a result of an accident, you can fall under her attack. Electric shocks occur due to contact with bare wires, switches, lamp sockets and other live household and industrial appliances, and failure to comply with safety precautions. Having received an electric shock, a person receives electrical injury, which may result in disability or even death.

What are the dangers of electric shock?

When exposed to electrical voltage, the victim always receives a shock, but its consequences can be different: from cramps of the fingers and trembling, from unpleasant sensations of heating and burning to respiratory arrest and cardiac fibrillation (unsystematic contraction) and its complete stop. In the latter case, blood stops moving through the vessels, causing the person to die. In addition, electric current is dangerous for humans, since at certain values ​​of its strength it creates the effect of sticking to bare wires due to excessive stimulation of nerve fibers by electricity. One of the causes of death from electric shock can be mechanical injury as a result of involuntary muscle contraction. Loss of vision may occur due to the impact of the resulting electric arc on the retina.

The skin on the face, neck and back of the palms is most affected by the effects of electric current.

Note! Certain (acupuncture) points on a person’s ears and neck are extremely susceptible to electricity - if they are hit, even a weak current can kill the victim.

Passing through the human body electric charge leaves peculiar marks on it - the so-called. "electrical marks", which are dead skin with a yellow coating, similar to calluses.

An electrical burn causes redness of the skin at the point of contact with its source, bubbles with physiological fluid inside are inflated, areas of the body become charred and blackened, sometimes pieces of metal or fabric from clothing are literally “melted” into them. Such burn injuries are treated worse than simple thermal burns; they do not always appear immediately - the consequences can become visible after hours, days or even months (therefore, all victims are under the supervision of doctors for a long time).

Most dangerous current– this is in the areas of the back, hands, temporal and occipital parts of the head.

The extent of health damage from electric shock depends on the direction of current movement inside the human body. As a rule, there are several “routes” for the passage of charge. The fatal path of current for a person is the path from one hand holding a bare wire to the other, because it goes through the lungs, bronchi and heart muscle and causes them to fibrillate. If the victim holds onto a source containing direct current with one hand and stands with his feet on the ground, the route is called “hand-foot”, in which case the electricity disrupts the functioning of almost all internal organs and, of course, the heart muscle. The “road” of electricity through the head to the arms or legs is also fatal: if the victim touches energized elements with his head. Sometimes people experience electrical injury from the so-called. “step voltage”, when they are on the ground that receives electric direct current without grounding, it passes through the body only through the legs, the heart does not suffer.

What current values ​​are deadly?

The depth and extent of electrical damage is influenced by three main factors:

• current frequency – variable in magnitude and direction or constant;
• current strength;
• direction of current as it passes through the human body.

According to the degree of influence on people’s health, the current is divided into:

• tangible - it only causes skin irritation to a person, a safe value is a current strength of up to 0.6 milliamps;
• non-releasing - alternating current, which, due to periodic impulses, causes a person to stick to the current source, this happens with a current strength of 0.025 amperes;
• fibrillation - causes fibrillation of internal organs, primarily the heart, which can lead to its stop; the strength of such a current exceeds 0.1 Ampere.

The body of any person resists electric current (described by Ohm’s law), its value depends on the general health of the victim at the time of the electrical injury, the degree of moisture, mental state and even the quality of shoes. Knowing the values ​​of electrical resistance, the values ​​of current voltage are displayed, which becomes dangerous to humans.

According to the canons of electrical safety technology, the following voltage values ​​are considered dangerous to human life and health:

• 65 volts - for residential premises and public buildings with heating and internal humidity not exceeding 60 percent;
• 36 volts – for rooms with increased level humidity up to 75 percent (for example, basements, kitchens in canteens and restaurants, metro station lobbies);
• 12 volts – for very humid (up to 100 percent) spaces (swimming pools, baths, laundries, rooms with boilers).

Additional Information. As for the frequency of the current, its value in the range of 50-60 hertz poses a danger to life.

If the current exceeds 50 milliamps, great harm is caused to health, and at values ​​above 100 milliamps, exposure to electricity even for a few seconds can kill a person.

Which current is more dangerous: alternating or direct?

Everyone knows that current can be alternating or constant, but not everyone understands which one is more harmful to life and health. Experts answer that the most dangerous is the variable type.

Why is alternating current more dangerous than direct current? The reason is that direct current must be three times more powerful than alternating current to be mortally dangerous to a person, since alternating current has a much stronger and faster effect on nerve endings and muscle tissue (primarily the heart). The DC power in many cases (with a power of up to 50 milliamps) is covered by electrical resistance human body, whereas for alternating electric current this limit is only ten milliamps. However, when electricity reaches a voltage of 500 volts, the harm from both types of current is the same, and when it is exceeded, direct current becomes more dangerous.

Our body is a conductor of electrical current, which, passing through it, has a detrimental effect on human health and can be fatal. The danger is posed not only by the strength, type and power of the current, but also by the duration of exposure and the route through the body. Current resistance depends on many conditions, so different countries have different standards that determine the safe voltage of electric current.

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Before you start independent work When dealing with electricity in your apartment or private home, you need to know that this work is very dangerous.

For a person, the voltage, which is already dangerous for his life, starts from 25 V.

As you know, electric current is invisible, inaudible and odorless. However, despite its invisibility, electricity makes electrical appliances work that light and heat homes. But this energy can easily go from creative to destructive and even deadly.

What is the danger of electric contact with a person? There are two main reasons:

• the first is mechanical damage to human tissue;
• the second is the effect of electricity on nervous system.

As is known, in humans the mechanism of transmission of nerve signals is based on an electrochemical nature. Simply put, man has his own electricity. With the help of nerve signals, muscles move, including the heart, and all internal organs are coordinated and controlled. In the event of contact with a live conductor, the human body reacts to this as a signal from its own nervous system, but much more powerful. The muscles contract convulsively, coming into a state of constant tension, and they cannot be relaxed, since the signal coming from outside far exceeds the commands of the body itself.

Everybody knows Golden Rule electricians - touch the exposed conductors with the back of your hand so that the muscles of the hand, having received an electric shock, clench the hand into a fist, thereby pushing the hand away from the contact.

Voltage from 25 V is considered dangerous for humans. In this situation, it is necessary to clearly distinguish between voltage and current. It is power that kills. For example: blue sparks of static discharges have a voltage of 7000 V, but have negligible strength, while the voltage in the outlet is 220 V but with a current of 10-16 A can cause death. Moreover, the passage of a current with a force of 30-50 mA through the heart muscle can already cause fibrillation (fluttering) of the heart muscle and reflex cardiac arrest.

How this will end is quite clear. If the current does not touch the heart (and the paths of electricity in human body are quite bizarre), then its effect can cause paralysis of the respiratory muscles, which also does not bode well. Absolutely amazing incidents happened when electric current, without leaving visible damage, literally fried internal organs, bringing them to a boil.

Mechanical damage to body tissues is divided into physical and chemical effects.

Physical impact

This is primarily thermal damage. The heat generated when electric current passes through a conductor (in this case, the human body) depends on the resistance of this conductor. This value for dry human skin is approximately 1000 Ohms, which is quite enough to cause burns of varying severity (this, of course, depends on the current strength and does not mean that contact of electricity with wet skin is preferable).

The resistance drops sharply, and the electrical discharge penetrates further into the human body, having a stronger effect on the internal organs.

Physical effects also include eye damage from electric arc flashes or short circuits. Harsh ultraviolet light can seriously burn the retina of the eye, causing short-term or permanent blindness, inversion of color vision, etc.

Chemical exposure

When a discharge passes through human tissue, the current changes the electrolytic properties of tissue fluid, blood, lymph, etc. This is fraught with serious consequences, since the composition of the blood is unchanged and should remain so. A shift in acidity levels, the properties of red blood cells and the chemical composition can cause severe damage to the body.

As can be seen from all of the above, almost any contact with electricity is, if not fatal, then very unpleasant. The degree of damage depends on the strength of the current and the time of exposure to the human body. The passage of a discharge through the human body does not always cause such serious consequences. According to statistics, for every 120-140 thousand cases of contact with electricity, only one ends in death.

Much more often there are situations where contact leads to injuries of varying severity. However, this is not a reason to treat electricity carelessly. Especially where people often come into contact with it: during electrical installation work or repairs. To minimize the risk of electric shock, it is necessary to thoroughly understand the basic safety rules and use protective equipment.

How dangerous is electric current?

Electric current is dangerous because it cannot be seen - this is an old joke, they like to ask it in exams and lessons.

Current passes through the human body in case of contact and this can be fatal. Be careful!

Electric current is dangerous because it is invisible, colorless and odorless. You should know that an AC voltage above 42 volts is considered dangerous, and a current of 0.1 A is already a fatal current. So, when repairing wiring, check that there is no voltage.

Electric current is dangerous for all living things, it leaves behind burns, and different ones depend on what voltage the current passes through you; if it is too high, then the person may not survive, since the current will affect the heart and brain cells, in this case, instant death, if the current not under high voltage, it can burn the internal tissues of a person.

Its main danger lies in the fact that it is not visible, and its fatal meanings for a person strike immediately

and on the spot. It takes a lot of endurance and observation to notice and ignore a protruding wire in time, and making sure others see it is a responsibility.

Electric current is dangerous for humans primarily because it affects the central nervous system, causing involuntary muscle spasms. Depending on the location of the shock and its direction in the body, the heart, lungs and other parts of the body may be affected.

The second danger is soft tissue burns.

And yet, despite the danger, many people have suffered one (or more) electric shocks from a household outlet in their lives, escaping with a slight fright and a slight burn :)

Electric current is dangerous because it can harm a person. When flowing through the human body, it burns internal organs and can be fatal. You need to be careful and attentive when working with electrical appliances.

There are two reasons for the danger of electric shock. The first is damage to the human nervous system, the second reason is mechanical damage to human soft tissues. When an electric shock occurs in the human nervous system, involuntary contraction of the muscles occurs and this continues as long as current flows through the human body. It is not for nothing that electricians check for voltage with the back of the right hand. Firstly, when the hand touches live parts, the hand contracts under the influence of electric current. the fist thereby pushes the hand away from live parts, secondly, with the right hand, and so that when an electric shock hits the human body, it does not hit the heart.

In case of mechanical damage to human soft tissues by electric current, it primarily affects the heart and other internal organs of a person, causing burns varying degrees, affect the eyes during a short circuit, the electrolytic properties of blood, tissue fluid, and lymph nodes change.

Electric current can be fatal to humans. If there is an electric shock even less than what is present in a regular household outlet, a person cannot independently tear himself away from the electrical wire.

You should also consider the path of current in the human body. The most dangerous path is considered to be the one that goes through the human heart. The result is heart rhythm disturbance.

When a person is exposed to current, it affects the central nervous system, disrupts cardiac activity and breathing, not to mention the fact that the person receives an electrical burn.

When a person is struck by an electric current of up to 1000 V, a spasm of the respiratory muscles, convulsions and cardiac arrest occurs.

Electric current is dangerous because it is invisible. Do not approach a broken wire lying on the ground closer than 10 meters. Otherwise, a step voltage zone will occur. The safe current value is 0.001 A, dangerous 0.01 A, lethal voltage 0.1 A. Electric shock does not pass without leaving a trace, it is life-threatening.

A real electrician must answer in the exam - With the fact that he is not visible.

It remains to add that the current is not visible under certain conditions.

After all, it happens that you can see it - electric welding, thunderstorms, other cases, including sparks from the eyes 😉

Electric current is dangerous for a person because when struck, the current runs throughout the body and leaves burns, it can also affect the heart, if there is a very high voltage then either instant death will occur or severe burns will remain, like my brother, he miraculously survived, more than 50% of his skin was burned .