Action El. Current on the human body, types of exposure, types of lesions

Electrical SocopaneSt.b is a system of organizational and technical measures and funds to protect people from harmful and hazardous impact electric current, electric arc and static electricity in order to reduce electrical exchanging to an acceptable risk level and below.

A distinctive feature of the electric current from other industrial hazards and harm (except radiation) is that a person is not able to detect electrical stress remotely with its senses.

In most countries of the world, accident statistics for the reasons for electricity shows that the total number of injuries caused by electric current with disability is small and is approximately 0.5-1% (in power engineering - 3-3.5%) on the total cost of accidents in production. However, with a fatal exodus, such cases in production are 30-40%, and in power engineering up to 60%. According to statistics, 75-80% of death lesions occurs in the installations to 1000 V.

The electric current flows through the human body if there is a potential difference between the two points. The voltage between the two points of the circuit of the current, which simultaneously concerns a person called voltage touch

Electric current action on human body

Passing through the body, the electric current causes thermal, electrolytic and biological effect.

Thermal actionit is expressed in the burns of individual parts of the body, heating blood vessels and nerve fibers.

Electrolytic actionit is expressed in the decomposition of blood and other organic fluids, causing significant violations of their physicochemical compositions.

Biological actionit is manifested in irritation and excitation of living woven organism, which can be accompanied by an involuntary convulsive cutting of muscles, including heart muscles and lungs. As a result, various violations of the body may occur, including violation and even complete cessation of respiratory and blood circulation bodies.

The irritating effect of the current on the fabric can be direct when the current passes directly along these tissues, and reflex, that is, through the central nervous system, when the current path is outside these organs.

The entire variety of electrical current action leads to two types of lesion: electrical injury and electric shocks.

Electrical injuries- These are clearly pronounced local damage to the body tissues caused by the exposure to electric current or electric arc (electric burns, electrical signs, leather metallization, mechanical damage).

Electric strike- This is the excitation of living tissues of the body passing through it by electric shock, accompanied by an involuntary convulsive cutting of the muscles.

Distinguish four degrees of electric blows:

A sitman - a convulsive cut of the muscles without losing consciousness;

Syrtepin - a convulse reduction of muscles with a loss of consciousness, but with the preserved breathing and work of the heart;

III Stensitive - loss of consciousness and violation of cardiac activity or respiration (or both together);

Issue - clinical death, that is, the absence of breathing and blood circulation.

Clinical ("imaginary") death- This is a transitional process from life to death, coming from the moment of termination of the heart and lungs. Duration clinical death It is determined by the time from the moment of cessation of cardiac activity and respiration before the beginning of the death of the cerebral cell cells (4-5 minutes, and with the death of a healthy person from random causes - 7-8 min.). Biological (true) death- This is an irreversible phenomenon, characterized by the cessation of biological processes in the cells and tissues of the body and the decay of protein structures. Biological death It occurs after the period of clinical death.

In this way, death causes from electric currentthere may be cessation of heart work, cessation of breathing and electric shock.

Heart stop or his fibrillation, i.e. chaotic fast and time-based cuts of the fibers (fibrils) of the heart muscle, in which the heart ceases to work as a pump, as a result of which blood circulation ceases in the body, may occur with direct or reflex operation of the electric current.

Termination of breathing as the root cause of death from the electric current is caused by the immediate or reflex effect of the current on the chest muscles involved in the respiratory process (as a result - asphyxia or chopping due to lack of oxygen and excess carbon dioxide in the body).

Types of lesions of electrical injuries:

- electric burns –

Electrometallization of skin

Electrical signs

Electric blows

Electrophthalmia

Mechanical damage

Electric burnand arise with thermal effect of electric current. The most dangerous are burns: resulting from the effects of an electric arc, the temperature may exceed 3000 ° C.

Electrometallization of skin- penetration into the skin under the action of the electric current of the smallest particles of metal. As a result, the skin becomes electrically conductive, i.e., the resistance drops sharply.

Electrical signs- Spots of gray or pale yellow, arising from dense contact with the current-carrying part (the PS of which in the working condition flows the electric current). The nature of electrical signs is not yet sufficiently studied.

Electrophthalmia- defeat the outer shells of the eye due to the impact ultraviolet radiation Electric arc.

Electric strikes - the overall lesion of the human body characterized by convulsive contractionsmuscles, impaired nervous and cardiovascular systems of a person. Often, electrical shocks lead to fatal outcomes.

Mechanical damage(tissue breaks, fractures) occur during a convulsive cutting of muscles, as well as as a result of drops when exposed to electric current.

The nature of electric shock and its consequences depend on the value and kind of current, the path of its passage, the duration of the impact, the individual physiological characteristics of the person and its condition at the time of the defeat.

Electric shock- This is a severe nervous reflex reaction of the body in response to strong electrical irritation, accompanied by hazardous circulatory disorders, breathing, metabolism, etc. This state can continue from a few minutes to day.

Basically, the value of the current determines the nature of the lesion. In electrical installations up to 500, an alternating current of industrial frequency (50 Hz) is more dangerous for a person than permanent. This is due to complex biological processes occurring in human body cells. With increasing current frequency, the danger of damage decreases. At frequency of the order of several hundred kilohertz, electrical strikes are not observed. Current, depending on the value of the human body, are divided into tangible, unknownand fibrillation.Tangible Toki.- Talks causing tangible irritations when passing through the body. A person begins to feel the effect of alternating current (50 Hz) at values \u200b\u200bfrom 0.5 to 1.5 mA and DC - from 5 to 7 mA. Within these values, there is a light shake of fingers, tingling, heating of the skin (at constant current). Such currents are called threshold tangible currents.

Unmissative Toki.cause a convulsive cut muscle. The smallest current value in which a person cannot independently tear his hands from the current-carrying parts, is called threshold uncomfortable current. For AC, this value lies in the range from 10 to 15 mA, for DC - T 50 to 80 mA. With a further increase in current begins the defeat of the cardiovascular system. It makes it difficult, and then breathing stops, the work of the heart changes.

fibrillation Toki.cause the heart fibrillation - fluttering or arrhythmic reduction and relaxation of the heart muscle. As a result of fibrillation, blood from the heart does not go into vital important organs And primarily the blood supply to the brain is disturbed. The human brain, devoid of blood supply, lives within 5 - 8 minutes, and then dies, so in this case it is very important to quickly and in a timely manner to give the first assistance to the victim. Fibrillation current values \u200b\u200brange from 80 to 5000 mA

Factors affecting the outcome of the defeat of EL. Tokom

The outcome of the exposure to the electric current on the human body depends on a number of factors, the main of which are: electrical resistance of the human body; the magnitude of the electric current; the duration of its impact on the body; the magnitude of the voltage acting on the body; Rod and current frequency; Path of current flow in the body; the psycho-physiological state of the body, its individual properties; Condition and characteristics ambient (air temperature, humidity, gas supply and dustiness), etc.

Tok PowerI.Current:

0,6 – 1,5 mA.: There is a feeling (change), it does not feel (last)

5 - 7mA.: crampsin the hands of (change), there is a feeling (permanent)

20 -25mA.: the threshold, not released - the hands are paralyzed, it is impossible to cut off from the equipment, slowing the breath (change), a slight muscle contraction (constant)

50 - 80mA.: fibrillation - Arrhythmic reduction or relaxation of heart muscles

	With alternating current 50 Hz	At constant toke
	The emergence of the feeling, easy finger shake	Not felt
	Cramps in the hands	The emergence of the feeling, heating the skin heating enhancement
	Hands are difficult, but you can still tear off the electrodes; strong pain In brushes and forearms	Strengthening heating
	Hands are paralyzed, to tear them off the electrodes is impossible, breathing difficult	Minor muscle contraction
	Stop breathing. Beginning of heart fibrillation	Strong heating; reduction of muscles of the hands; Difficult breathing
	Stop breathing and cardiac activity (with the duration of exposure more than 3 s)	Stop breathing

The duration of the current effect on the human body- One of the main factors. The shorter the time of exposure to the current, the less danger.

If the current is unrequisite, but does not yet break the breath and work of the heart, the rapid shutdown saves the victim, who could not free himself. With prolonged exposure of current, the human body resistance drops and the current increases to the value capable of bringing the respiratory stop or even the heart fibrillation.

Stopping respiration occurs not instantly, but after a few seconds, and the more current through a person, the less time it is. Timely shutdown of the victim makes it possible to prevent the termination of the operation of the respiratory muscles.

Thus, the less the duration of the current action per person, the less the probability of the coincidence of the time during which the current passes with the phase of T.

Current path in the human body. The most dangerous passage of current through the breathing muscles and the heart. So, it was noted that on the way "hand-hand" through the heart passes 3.3% of the total current, " left hand - Legs "- 3.7%," Right hand - legs "- 6.7%," foot - leg "- 0.4%," Head - legs "- 6.8%," Head - Hands "- 7 %. According to statistics, working capacity loss for three days and more was observed at the time of the current "hand - hand" in 83% of cases, "left hand - legs" - in 80%, "Right hand - legs" - 87%, "Leg - leg" - In 15% of cases.

Thus, the current path affects the outcome of the lesion; The current in the human body is not necessarily through the shortest path, which is explained by a large difference in the specific resistance of various tissues (bone, muscular, well, etc.).

The smallest current through the heart passes upon the path of the current at the bottom loop "foot - leg". However, this should not draw conclusions about the low risk of the bottom loop (step by step voltage). Usually, if the current is large enough, it causes the feet cramps, and the person falls, after which the current can already pass through the chest, i.e. through the breathing muscles and the heart. Most dangerous- this is the path passing through the head and spinal cord, heart, lungs

Rod and current frequency. It has been established that the alternating current with a frequency of 50-60 Hz is more dangerous than the permanent one. Since the same effects are caused by large DC values \u200b\u200bthan variable. However, even a small constant current (below the sensation threshold) with a rapid break of the chain gives very sharp blows, sometimes causing arm muscles.

Many researchers argue that alternating current is most dangerous with a frequency of 50-60 Hz. The danger of the current is reduced with increasing frequencyBut current 500 Hz frequency is no less dangerous than 50 Hz.

Resistance to human bodyit is imperceptible and depends on many factors - the status of the skin, the magnitude and density of the contact, the applied voltage and the time of exposure to the current.

Usually, when analyzing the risk of electrical networks and, in the calculations, it is considered to consider the resistance of the human body as active and equal to 1 com.

The nature of the lesion depends on the time of operation of the current. With prolonged exposure to current, the heating of the skin increases, the skin due to the removal is moistened, the resistance is dropped and the current passing through the human body increases sharply.

The nature of the damage is determined by the individual physiological characteristics of a person. If a person is physically healthy, then the electroporation will be less severe. In case of diseases of the cardiovascular system, the skin, nervous system, with alcoholic intoxication, the electrician may be extremely serious even with small acting currents.

An important impact on the outcome of the defeat has psycho-physiological preparedness of the employee to effect. If a person is attentive, concentrated when performing work, prepared for the fact that it can be exposed to electric current, then injury may be less severe.

Environmental parameters: Temperature, humidity, dust availability

Physiological features of the body at the moment of defeat

Applied Voltage Dependency Direction Direction

Current phenomenon in the ground

P beat "Leg - Leg" is the least dangerous. Most often, this path occurs when a person falls under the influence of the so-called step voltage, i.e. between the points of the earth's surface, which are at a distance of the step from each other.

If there is a closure on the Earth of any chain - a random electrical connection of the current-carrying part directly from the ground or through the metal structures, the electric current will be raised on the ground, called current closure on the ground.The potential of the Earth as the closure is removed from the site will vary from maximum to zero value,

since the soil has resistance to the current circuit.

Fig.1 Inclusion of a person on the tension of the step

If a person falls into a current spreading zone, there will be a potential difference between its feet, which will cause current flow along the path of "foot - leg". The result of current impact may be the contraction of the muscles of the legs, and the person can fall. The fall will cause education. A more dangerous circuit of passing the current through the heart and lungs.

In fig. 3.1 shows the formation of step voltage and the potential distribution curve is shown on the ground surface. At a distance of 20 m from the location of the closure, the potential can be considered equal to zero. Fig. 3.1. Inclusion of a person on a step voltage

The value of the current passing through the human body depends on the applied voltage and resistance of the body. The greater the voltage, the greater the current passes through the person

(I 2 - the path of passage is more dangerous and more higher than the current)

Touch voltage and step

Stepper voltage - stress on the surface of the earth between points located at a distance of the step from each other.

Touch voltage is the difference in the potentials of two points of electric. The chains of which simultaneously concerns a person.

To reduce the difference φ 2 -φ 1, from the spreading zone you need to go out with small chambers

Classification of premises by the degree of danger of electric shock

Electrical installationscalled the installations in which it is transformed is converted, electrical energy is distributed and consumed. Electrical installations include generators and electric motors, transformers and rectifiers, wired, radio and television equipment, etc.

Safety of work in electrical installations depends on the electrical circuit and parameters of the electrical installation, rated voltage, the environment and operating conditions. From the point of view of security, all electrical installations according to PUE are divided into installations up to 1000 V and the installation above 1000 V. Since the settings above 1000 V are more dangerous, then more stringent requirements are presented to protective measures.

Electrical installations can be located in closed rooms and outside them. Environmental conditions have a significant impact on the state of insulation of the electrical installation,

resistance to human body, and therefore safe? service personnel. Conditions for working according to the degree of electrical safety are divided into three categories: with an increased risk of "lesions of people with electric shock; especially dangerous; without increased danger.

Conditions S. increased dangercharacterized by the presence of one of the following features: - Conductive bases (reinforced concrete, earthy, metal, brick);

Conductive dust, worsening cooling conditions for isolation, but not causing fire hazards;

Dampness (relative humidity exceeding 75%);

Temperature, long exceeding + 35 ° C;

The possibility of simultaneously touching a person to grounded metal structures, on the one hand, and to the metal housings of electrical equipment - on the other.

To reduce the risk of electric shock, under these conditions, a small voltage is recommended (not more than 42 V).

Particularly dangerous conditionscharacterized by the presence of one of the following features:

special dampness (relative humidity close to 100%);

chemically active medium that destructs insulation and current-carrying parts of electrical equipment;

at least two signs with increased danger.

In conditions without increased danger, there are no signs

Electrical injuries: burn, skin metallization, mechanical damage.

The effect of electric current on the human body is peculiar and wearing a versatile character. Electric current, passing through the human body, has a thermal, electrolytic and biological effect on various systems organism. At the same time, there may be violations of the vital human resources: the brain, heart and lungs.

All types of electrical current action on the human body can be combined into two main: electrical injuries and electrical shocks.

Electrical injuries are local body damage: burns, leather metallization, mechanical damage to the body.

Burnit may be caused by the passage of the electric current directly through the human body or an electrical arc on it. Electric arc burns are most dangerous and have severe consequences, since the temperature of the electrical arc exceeds 3500 ° C.

Metalization of the skinit occurs due to penetration into its upper layers of the smallest metal particles, evaporated or melted under the action of an electrical arc. This type of damage is also possible as a result of electrolytic current.

Mechanical damageare a consequence of involuntary contractions of the body's muscles under the action of current. At the same time, it is possible to break the skin, blood vessels and nervous tissue, dislocations of the joints and even bone fractures. This type of injuries also include bruises and fractures associated with a falling person from height, blows about equipment or elements of the building as a result of involuntary motion or loss of consciousness when exposed to current.

A type of electrician is electrophthalmia - eye damage caused by intense radiation of an electric arc, in the spectrum of which are harmful to eyes ultraviolet and infrared rays.

Electric strike It causes the excitation of alive tissues of the body passing through it by electrical current, accompanied by involuntary convulsive cuts of muscles, including the muscles of the heart and lungs. As a result, various violations of the body's vital and even complete cessation of respiratory and blood circulation bodies may occur.

The following classification of electricians in the extent of their gravity are adopted: I - a convulsive muscle contraction without losing consciousness; II-sustain cutting muscles with loss of consciousness, but with the preserved breath and heart work; Iii - loss of consciousness and violation of cardiac activity or respiration, and possibly their joint violation; IV - clinical death characterized by the absence of breathing and blood circulation.

Clinical death is a transitional period from life to death, coming from the moment of termination of the heart and lungs. A person who is in a state of clinical death has no sign of life - does not breathe, the heart does not work, the pupils of the eyes are expanded and do not react to light, pain irritations do not cause any reactions. Meanwhile, during this period, life in the body has not yet completely faded. A person can be in a state of clinical death from 4-5 to 8-10 min, depending on the type and severity of the defeat and individual characteristics of the body.

The nature and consequences of human damage to electric shock depend on a number of factors: electrical resistance The human bodies, the size and duration of flowing through it current, genus and frequency of the current, ways to pass the current in the human body, the individual properties of the human body, etc.

The electrical resistance of human body is inhomogeneously. Skin, bones, fat fabrics have greater resistance than blood, spinal and brain, muscle. The skin has the highest specific resistancedetermining the resistance of the entire body of a person.

When moisturizing and pollution, as well as skin damage, the resistance of the body is dramatically reduced (Fig. 65). Body resistance decreases also with increasing current and time of its flow.

Fig. 65. The dependence of the resistance of the human body from voltage at a frequency of 50 Hz:

a - dry skin; b - wet skin

When calculating the resistance of the human body is taken equal to 1000 ohms.

The power of the electric current passing through the human body is the main factor determining the outcome of the damage. The more the current strength, the more dangerous its action.

According to the consequences of the physiological impact on the human body, electric current can be divided into a threshold tangible, the threshold is inclusive, threshold fibrillation.

Threshold tangiblethe current having small values \u200b\u200b(from 0.6 to 1.5 mA) causes the first tangible effects, but does not injure. The threshold is unsolvedcurrent current is considered 10-15 mA. Under its impact, almost eliminated the possibility of self-separation of a person from current-carrying plants.

A current of more than 100 mA is considered deadly, which causes paralysis of respiratory organs and heart fibrillation and is called threshold fibrillation.

The longer the person is under the influence of the current, the more serious the consequences of the defeat. In this regard, it is necessary to help the affected freight from contact with the installation under dangerous voltage as possible, since with a long-term passage of 25-50 mA, a deadly outcome is possible. It is explained by the fact that the resistance of the human body with long-term passage of the current decreases as a result of progressive heating and breaking the horn layer of the skin. In addition, the long-term passage of alternating current violates the rhythm of cardiac activity, causing the trembling of the ventricles of the heart due to the damage to the nerves of the heart muscle. For AC, a frequency of 50 Hz is considered a permissible value: with long-term exposure (not limited time), 1 mA, when exposed to 0.1 s - 500 mA and 1.0 s - 65 mA.

The genus and the frequency of the current also affect the severity of the lesion. The variable current is most dangerous with a frequency of 50 Hz.

Permanent current of the same variable variable causes weaker muscle contractions and less unpleasant sensations.

At constant current, threshold values \u200b\u200bincrease: for tangible current up to 6-7 mA and unsubstantive current up to 50-70 mA. Its action is mainly thermal, but burns can be very heavy and even fatal. A smaller risk of DC is limited to a voltage value of 250-300 V. With a greater voltage, the constant current also becomes dangerous. The applicable rules of the device and the operation of electrical installations are the same for both AC and for DC.

The path of passing through the human body also affects the outcome of the lesion, since individual tissues have different resistances. The current passes not by the shortest distance between the electrodes, and mostly along the flow of tissue fluid, blood and lymphatic vessels and shells of nerve trunks with the greatest electrical conductivity. Fabrics internal organs are the worst current conductors. Connecting tissue, dry skin and bone fabric can be attributed even to dielectrics. The greatest danger Presents the passage of current, through vital organs: the heart, spinal cord, respiratory organs, etc. Such a danger arises along the way "Hand - Feet" or "Hand". Heavy lesions are not excluded and when the current is passed on the least dangerous path of the foot - foot (under step voltage).

Individual properties of a person greatly affect the outcome of the defeat. Healthy and physically strong people easier tolerate electric current compared to suffering various diseases. It should be borne in mind that it matters not only the physical, but also the mental state of the victim at the time of the occurrence of the electric shock. Persons suffering from heart diseases, internal secretion organs, nerve diseases, tuberculosis, etc., as well as in a state of overwork, fatigue, alcohol intoxication, are susceptible to greater danger of electric shock.

As a result, the maintenance of electrical installations is entrusted to persons who have passed not only special training, but also a medical examination.

The affecting effect of electric current on the human body is customary to be called electric shock. It is necessary to take into account that this type of production injuries is peculiar big number Exodues with severe and even mortal consequences. Below is a graph showing the percentage of them.

As statistics show, the greatest percentage of electricians (from 60 to 70%) is to operate electrical equipment up to 1000 volts. This indicator is explained as the prevalence of installations of this class and weak preparation of working personnel.

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

Labor protection requires everything to work with electrical equipment, the electrical safety instruction is mandatory. Where it tells about the danger of electrotock, what measures need to be taken with electricians, as well as ways to provide assistance in these cases.

Note that the number of electricians is significantly lower among those serving electrical equipment with a voltage over 1000V, this indicates good preparation Such specialists.

Factors affecting the outcome of electric shock

There are several dominant reasons from which the nature of damage during electrical inspection is depends:

Types of exposure

Electric strengths from 0.5 to 1.5 mA is considered minimal for perception by a person when it takes exceeding this threshold, a feeling of discomfort begins to appear, which is expressed in an involuntary reduction. muscular fabric.

At 15 mA and the control over the muscle system is more completely lost. In this state, without helping, it is not possible to break away from the electrical source, therefore, this threshold value of the power of the electric coo is called non-consumable.

With the power of electric flow, the turning line of 25 mA, the muscle paralysis occurs, responsible for the operation of the respiratory system, which threatens the suffocation. If this threshold is significantly higher, fibrillation occurs (cardiac rhythm failure).

Video: Electric current action on human body

Below is a table where the valid voltage, current and time of their exposure is indicated.

Electricalrams can produce the following types of influences:

• the heat, there are burns of varying degrees that can disrupt the work of both blood vessels and internal organs. We note that the thermal manifestation of the operation of the electric flow is observed with most electricians;
• the effects of electrolytic nature causes changes in physical and chemical composition tissues, due to blood splitting and other body fluids;
• physiological, leads to convulsive cuts of muscle tissues. Note that the biological effect of electrotock also violates other important organs, for example, heart and lungs.

Types of electrical workers

The effect of electrotock causes the following characteristic damage:

• electrologies may occur due to the passage of electric flow or be caused by an electric arc. Note that such electricians are most often occurring (about 60%);
• the appearance on the skin of oval spots of gray or yellow in places of passage of electric flow. Dead layer skin cover It cuts out, after a while, such an education called an electric sign, independently comes off;
• penetration of small metal particles (melted from KZ or electric arge) into the skin. This type of injury is called metallization of the skin. For affected areas, a dark metal hue is characterized, touching it causes painful sensations;
• the light effect becomes the cause of electrophthalmia ( inflammatory process Eye shell) due to ultraviolet radiation characteristic of the broadcast. To protect it is enough to use special glasses or a mask;
• mechanical impact (electric shock) occurs due to involuntary reduction in muscle tissue, as a result of this, the gap of the skin or other organs can happen.

Note that the effects of electrical strikes described above the electric shocks described above are the effects of electrical impact, they are separated according to the degree of exposure:

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

Step tension

Given the frequent cases of defeat from step tension, it makes sense to tell more about the mechanism of its impact. Open the power line, or disruption of the integrity of isolation in the cable laid under the ground lead to the formation around the conductor of the hazardous zone, in which the "spreading" current occurs.

If you get into this zone, you can expose the stress of the step, its value depends on the difference in the potentials between the places where the person concerns the Earth. The figure shows a clearly demonstrated as it happens.

Figure marked:

• 1 - electrical wiring;
• 2 - the fall of the cut-off wire;
• 3 - a man who fell into an electric shock zone;
• U 1 and U 2 - potentials at points where the legs come into contact with the ground.

Step voltage (V w) is determined by the following expression: U 1 -U 2 (B).

As can be seen from the formula, the more the distance between the feet, the more significant potential difference and above V w. That is, if the expansion of the electrotock occurs, where the "spreading" is "spreading", it is impossible to make big steps to exit.

How to act, providing assistance in electric worms

First aid with electric shock lies in a certain sequence of actions:

Electromagnetic wave, spreading from the source in an unlimited space at the speed of light, creates an electromagnetic field (EMF) capable of acting on charged particles and currents, resulting in the transformation of the field energy into other types of energy.

The active beginning of the oscillations of the range from units to several thousand Hz are flowing currents of the corresponding frequency through the body as a good conductor.

For a frequency range from several thousand to 30 MHz, a rapid increase in energy absorption is characterized, and therefore absorbed body capacity with increasing oscillation frequency. A feature of the range from 30 MHz to 10 GHz is the "resonant" absorption. A person has such a nature of the absorption in the action of EMF with frequencies from 70 to 100 MHz. For ranges from 10 to 200 GHz and from 200 to 3000 GHz, the maximum energy absorption with surface tissues, mainly skin, is characterized.

With a decrease in wavelength and increasing the frequency of the depth of penetration electromagnetic waves The fabric decreases. This trend is observed until the wavelength in this organism significantly exceeds the size of the cell. At very high frequencies, the permeability of tissues for electromagnetic radiation again begins to increase, for example, for X-ray and gamma radiation.

The difference in the dielectric properties of tissues leads to the uneven heating, the occurrence of macro- and micrometallic effects with a significant temperature difference.

Electromagnetic fields of industrial frequency

Long exposure to electromagnetic fields of industrial frequency (50 Hz) leads to disorders in the brain and central nervous system . As a result, man is observed headache in temporal and occipital regions, lethargy, worsening memory, heart pain, oppressed mood, apathy, peculiar depression with increased sensitivity To bright light and intense sound, sleep disorder, cardiovascular system, digestive, respiration organs, increased irritability, and also there are functional disorders in the central nervous system, changes in blood composition.

According to the sanitary rules and norms of SanPiN 2.2.4.1191-03 "Electromagnetic fields under production conditions" Stay in electromagnetic fields of industrial frequency up to 5 kV / m intensifies during the entire working day.

Electrostatic fields

The electrostatic field (ESP) forms electrostatic charges arising on the surfaces of certain materials both liquid and solid, due to electrification.

Electrification occurs with the friction of two dielectric or dielectric and conductive materials, if the latter is isolated from Earth and. When separating two dielectric materials, electric charges are separated. A material having a large dielectric permeability is charged positively, and less - negative.

In addition to friction, the cause of static charges is an electric induction, as a result of which the electrical charge is acquired from the body in the external electric field.

The impact of ESP per person is associated with the flow of a weak current. In this case, the electrician does not happen. However, due to the reflex reaction to irritation of analyzers on the skin, a person is removed from the charged body, which can lead to mechanical injury From the strike of nearby arrangements of structures, drop from height, fright with a possible loss of consciousness.

The electrostatic field of high tensions (several tens of kilovolt) can change and interrupt cellular development, cause cataract with subsequent closet of lens.

To the effects of the electrostatic field the most sensitive central nervous and cardiovascular system, analyzers. People complain of irritability, headache, sleep impairment, decline of appetite, etc. Long-term residence of a person under conditions when ESP tensions have a value of more than 1 kV / m, causes nervous emotional tension, fatigue, reduction of working capacity, disorded biorhythm, reduction of adaptation Reserves of the body.

Extremely permissible value ESP tensions are installed by SanPine 2.2.4.1191-03, depending on the time of its impact on the employee for a shift, equal to 60 kV / m for 1 hour. With an ESP tension of less than 20 kV / m, the residence time in the field is not regulated.

With the tension of ESPs exceeding 60 kV / m, the work without the use of the means of protection is not allowed.

Electromagnetic fields of radio frequencies

The electromagnetic fields of the radio frequency of large intensity are caused by the thermal effect in the human body, which can be expressed in the heating of the body, or its individual tissues or organs. The impact of the electromagnetic field is especially harmful for organs and tissues, not enough well-supplied blood vessels (eyes, brain, kidneys, stomach, urinary and gallbladder). The most sensitive to the impact of radio waves is a central nervous and cardiovascular system. Human has a headache, increased fatigue, change arterial pressure, neuropsychiatric disorders, and can also be observed hair loss, nail fragility, weight loss.

The rationing of the EMF radio frequency range under production conditions is carried out by SanPine 2.2.4.1191-03, according to which the impact of EMF radio frequencies on people is carried out on the intensity of radiation and the energy exposure.

The maximum permissible levels (remote control) of the electric and magnetic fields (EPDA, NAPU) of the frequency range from 10 to 30 kHz under exposure throughout the work shift are 500 V / m and 50 cars, respectively. The flow of electric and magnetic fields with duration of exposure to 2 hours per shift is 1,000 V / m and 100 cars, respectively.

Ways to protect against the harmful effects of electromagnetic fields

Protection of a person from the dangerous effects of electromagnetic irradiation is carried out in the following ways: reducing radiation from the source; shielding of the source of radiation and workplace; establishing a sanitary protection zone; absorption or decrease in the formation of static electricity charges; elimination of static electricity charges; Application of personal protective equipment.

Reducing the radiation power from the source is implemented by the use of electromagnetic energy absorbers; Blocking radiation.

Absorption electromagnetic radiation It is carried out by the absorption material by turning the energy of the electromagnetic field into thermal. The rubber, foam rubber, polystyolster, ferromagnetic powder with a binding dielectric are used as such material.

Screening of the source of radiation and workplaceperformed by special screens. At the same time distinguish reflecting and absorbing screens. The first are made of low electrical material - metals and their alloys (copper, brass, aluminum, steel, zinc). They can be solid and mesh. Screens must be grounded to secure charges to the ground for them.

The absorbing screens are performed from radio absorbing materials: elastic or rigid foams, rubber rugs, foam rubber sheets or fibrous wood treated with special composition, as well as from ferromagnetic plates.

To eliminate the charges of static electricity, grounding of equipment parts, air moisturizing is used.

Electricity

The danger of lesions of people by electric current in production and in everyday life appears in non-compliance with security measures, as well as when refusing or malfunction of electrical equipment and household appliances. Compared to other types of industrial injuries, electric evils is a small percentage, but by the number of injuries with severe and especially father outcome It takes one of the first places. In production, due to non-compliance with the rules of electrical safety, 75% of electroporation occurs.

The effect of electric current on the living tissue is versatile and peculiar. Passing through the human body, electrotes produces thermal, electrolytic, mechanical, biological, light effect.

Thermal effect of current characterized by heating of the skin and tissues to high temperatures Up to burns.

Electrolytic impactlies in the decomposition of organic fluid, including blood and violation of its physicochemical composition.

Mechanical action The current leads to a bundle, rupture of the body tissues as a result of an electrodynamic effect, as well as instantaneous explosion-like formation of steam from tissue fluid and blood. Mechanical action is associated with a strong reduction in muscles up to their rupture.

Biological action It is manifested in the irritation and excitation of living fabrics and is accompanied by convulsive cuts of muscles.

Light action leads to the defeat of the mucous membranes of the eyes.

Types of human body electric shock

Electrocama - These are injuries obtained from the effects of electric current on the body, which are conventionally divided into common (electrical strike), local and mixed.

Electric strike

An electric blow is the excitation of live tissues of the body passing through it by electrical current, accompanied by sharp convulsive cuts of muscles, including the muscles of the heart, which can lead to a heart stop.

Under local electricians are understood as damage to the skin and muscle tissue, and sometimes ligaments and bones. These include electric burns, electrical signs, leather metallization, mechanical damage.

Electric burns

Electric burns are the most common electric shock, arises as a result of local exposure to the tissue. Burns are two species - contact and arc.

Contact burn It is a consequence of the transformation of electrical energy into thermal and occurs mainly in electrical installations by voltage to 1,000 V.

Electric burn- It's like an emergency system, the protection of the body, since charred tissues due to greater resistance than ordinary skin, do not allow electricity to penetrate deep into, to vital systems and organs. In other words, thanks to the burn, the current goes to a dead end.

When the body and the voltage source matted loosely, burns are formed in the fields of input and current output. If the current passes through the body several times different ways, multiple burns occur.

Multiple burns most often occur at a voltage of up to 380 in due to the fact that such a voltage "multiplies" a person is required to disconnect. High voltage current does not possess such a "lipacitation". On the contrary, he discards a person, but also such a short contact is enough for serious deep burns. At a voltage of more than 1,000, electric crawls happen with extensive deep burns, since in this case the temperature rises throughout the current route.

At voltage over 1 000 B as a result of random short circuits, arc burns may occur.

Electrical signs and electric marks

Electrical signs or electrical labels are clearly defined spots of gray or pale yellow on the surface of a person's skin, subjected to current action. Typically, electrical signs have a round or oval shape with an in-depth in the center size from 1 to 5 mm.

Metalization of the skin

Metalization of the skin is loss of the smallest particles of molten metal on open skin surfaces. Typically, such a phenomenon occurs with short circuits, the production of electric welding works. On the affected area there is pain from the burn and the presence of foreign bodies.

Mechanical damage

Mechanical damage - a consequence of convulsive cuts of muscles under the action of a current passing through a person leading to a tearing of skin, muscles, tendons. This happens at a voltage below 380 V, when a person does not lose consciousness and is trying to free themselves from the current source.

Factors determining the outcome of the exposure of electric current per person

According to GOST 12.1.019 "SSBT. Electrical safety. General requirements "degree of dangerous and harmful effects The electric current depends on the strength, voltage, the generation, the frequency of the electric current and the path of passing through the human body, the duration of exposure and the conditions of the external environment.

Tok Power - The main factor on which the outcome of the lesion is depends: the greater the power of the current, the more dangerous consequences. The strength of the current (in amperes) depends on the applied voltage (in volts) and the electrical resistance of the body (in Omah).

According to the degree of impact on a person, three threshold values \u200b\u200bof the current are distinguished: tangible, uncomfortable and fibrillation.

Tangible

Tangible is called electric current, which, when passing through the body, causes tangible irritation. The minimum value begins to feel a person with a variable current with a frequency of 50 Hz is 0.6-1.5 mA.

Uncomfortable

An irrepresentant consider the current in which the insurmountable convulsive cuts of the muscles of the arms, legs or other parts of the body do not allow the victim to sieve independently from the current-carrying parts (10.0-15.0 mA).

Fibrillation current

The fibrillation - current causing when passing through the body of the heart fibrillation - fast chaotic and divergent reductions of the fibers of the heart muscle, leading to its stop (90.0-100.0 mA). After a few seconds, breathing stops. Most often, deadly outcomes occur from voltage 220 V and below. It is the low voltage that causes the heart fibers randomly and leads to an instant failure in the work of the heart of the heart.

Safe current

This should be considered a current at which a person can free themselves from the electrical circuit. Its value depends on the speed of the current through the human body: with the duration of action more than 10 C - 2 mA, and at 120 s and less - 6 mA.

36 V (for lamps of local stationary lighting, portable lamps, etc.) and 12 V (for portable luminaires during operation inside the metal tanks, boilers) are considered safe voltage. But with certain situations, such stresses may be dangerous.

Safe voltage levels are obtained from the lighting network using lower transformers for this. Disseminate the use of safe voltage to all electrical devices is not possible.

IN production processes Two clauses are used - Permanent and variable. They have different impact on the body at stresses up to 500 V. Danger of damage to constant current less than variable. The greatest danger represents the current with a frequency of 50 Hz, which is standard for domestic electrical networks.

The path in which the electric current passes through the human body largely determines the degree of damage to the body. The following variants of the current movement of the current of the human body are possible:

• man with both hands is adopted to the current-carrying wires (parts of the equipment), in this case there is a direction of flow of current from one hand to another, i.e., "hand-hand", this loop is most often occurring;
• when touched one hand to the source, the current path closes through both legs to the Earth "Hand-Feet";
• when testing the insulation of the current-carrying parts of the equipment on the case under voltage, there are hands working, at the same time flowing the current from the equipment body to the ground leads to the fact that the legs turn out to be energized, but with another potential, so the path of the "hands-leg" current occurs;
• when flowing the current on the ground from the faulty equipment, the land of nearby receives the changing potential of the voltage, and the person who comes with both legs on such an earth is under the difference in potentials, i.e., each of these legs receives a different voltage potential, as a result, step tension occurs and electrical circuit "Foot leg", which happens less often and is considered the least dangerous;
• the touch of the head to the current-generating parts can cause the path of the current on the hands or on the legs of the work performed, the head-hand, "head-leg".

All options vary in the degree of danger. The most dangerous are the options "head-hands", "head-leg", "hands-legs" (hinge full). This is explained by the fact that vital systems of the body fall into the lesion zone - the brain, heart.

Duration of current exposure affects the final outcome of the lesion. The longer the electric current on the body is impact, the harder the consequences.

Conditions of the external environment, surrounding man In the course of industrial activity, they can increase the risk of electric shock. Increase the danger of lesion to the current increased temperature and humidity, metal or other conductive floor.

By degree of danger Man defeats all rooms are divided into three classes: without increased danger, with increased danger, especially dangerous.

Electric Current Protection

To ensure electrical safety, it is necessary to accurately comply with the rules for the technical operation of electrical installations and carrying out measures to protect against electrical exchanging.

GOST 12.1.038-82 Sets the maximum allowable stresses and currents flowing through the human body at normal (non-accidental) mode of operation of electrical installations of industrial and domestic purposes of direct and alternating current with a frequency of 50 and 400 Hz. For AC 50 Hz, the allowable value of the tension voltage is 2 V, and the current forces is 0.3 mA, for the current with a frequency of 400 Hz - 2 V and 0.4 mA, respectively; For DC - 8B and 1.0 mA (these data are shown for duration of exposure not more than 10 minutes per day).

Measures and electrical safety methods are:

• use of safe voltage;
• control of insulation of electrical wires;
• elimination of random touch to the current-generating parts;
• device of protective grounding and reassembling;
• use of personal protective equipment;
• compliance with the organizational measures to ensure electrical safety.

One of the aspects can be the use of safe voltage - 12 and 36 V. To obtain it uses downward transformers, which include in a standard network with a voltage of 220 or 380 V.

To protect against accidental touch of a person, fences in the form of portable shields, walls, screens are used to the current-generating parts of electrical installations.

Protective grounding - This is a deliberate electrical connection with the land or its equivalent (metal structures, etc.) of metal inadvertent parts, which may be energized. The purpose of the protective ground is to eliminate the danger of human damage to electric current in the case of contacting it to the metal body of electrical equipment, which, as a result of the insulation, was substituted.

Stage - a deliberate electrical connection with a zero protective conductor of metal inadvertent parts, which may be under voltage. The zero protective conductor is a conductor connecting the bottom-down parts with a deaf-free neutral point of winding of the current source or its equivalent.

Protective shutdown - This is a security system that provides safety by quickly automatically shutting down the electrical installation in it occurs in it the danger of damage to the current. The response duration of the protective shutdown is 0.1-0.2 s. This method Protection is used as the only protection or in combination with protective grounding and rewarding.

Application of small stresses. Small refer to 42V voltage, it is used when working with portable power tools, using portable lamps.

Isolation control. Wiring isolation over time loses its dielectric properties. Therefore, it is necessary to periodically monitor the resistance of the insulation of the wires in order to ensure their electrical safety.

Individual protection means - divided into insulating, auxiliary, enclosing. Insulating protective facilities provide electrical insulation from the circulating parts and earth. They are divided into main and extra. The main insulating means in electrical installations up to 1000 V are the dielectric gloves, the tool with insulated handles. Additional means - dielectric galoshes, mats, dielectric stands.

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How does electric current affect a person?

Electrical injuries

Electric current is striking a person suddenly. Current passage through the human body causes electrical injuries various character: Electric blow, burns, electrical label signs.

An electric blow is a lesion of a current in which shock occurs, that is, a peculiar severe response of the organism on a strong stimulus is an electric current.

The outcome of the shock is distinguished. In severe case, shock is accompanied by circulatory disorder and respiratory. Heart fibrillation is possible, that is, instead of the simultaneous rhythmic (approximately 1 time per second), the reduction of the cardiac muscle occurs a chaotic twitching of its individual fibers - fibrils. It stops normal work Hearts, blood flow stops, and death may come.

Man's defeat with a current at a voltage of up to 1000 V in most cases is accompanied by an electrical impact.

Burns arise when exposed to a considerable value (about 1 BUT or more) or from an electric arc. So, when approaching the current-generating parts, the voltage above 1000 V is unacceptably a small distance between the current-carrying part and the body of the person appears a spark discharge, and then an electric arc that causes a heavy burn. In case of random contact with the current-carrying part of the voltage up to 1000, the current passing through the body heats the tissue to 60-70 ° C. This causes the coagulation of the protein. Electric shock burns are difficult. They capture the large surface of the body and penetrate deeply.

Electrical signs (tags) are a leather coloring in the form of a yellow corn with a gray border at the entrance and current output. If the defeat penetrated deeply, then the body tissues gradually die.

The nature of the effect of an alternating electric current depending on its value is given in Table. one

From table. 1 It follows that it is dangerous for a person is the current of more than 15 mA, in which a person cannot free himself. The current of 50 mA causes severe defeat. The current of 100 mA, which is impaired more than 1-2 s is fatally dangerous.

Factors affecting the outcome of damage

The magnitude of the electric current passing through the human body, and therefore, the outcome of the damage depend on many circumstances.

The most dangerous is the variable current with a frequency of 50-500 Hz. Most people retain the ability to independently free themselves from the currents of such a frequency with very small values \u200b\u200b(9-10 mA). Permanent current is also dangerous, but independently free from it possible with several large quantities (20-25 mA).

The value of the current depends on the electrical installation voltage and on the resistances of all the chain elements on which the current flows, including the resistance of the human body. Body resistance is composed of active and capacitive resistances of the skin and internal organs . Dry, intact leather has a resistance of about 100,000 ohms, wet - about 1000 ohms, and the resistance of the inner tissues (with a lit-off layer shot) is approximately 500-1000 ohms. The smallest resistance is the skin of the face and axillary depression.

The human body resistance is non-linear. It is sharply, disproportionately decreases with an increase in the applied to the body of the voltage, increasing the time of exposure to the current, with unsatisfactory physical and mental state, with a large and dense contact with the current-carrying part, etc. from fig. 1 It follows that with an increase in the voltage attached to the body from 0 to 140, the body resistance is nonlinearly falling from tens of thousands to 800 ohm (curve 1). Accordingly, the current passing through the body increases (curve 2).

The resistance of the human body (OM) is approximately determined by the formula

Z people \u003d u pr / i person

where U PR- the drop in the voltage on the resistance of the body of a person - V.

In its electrical safety calculations (also approximately), they are taken equal to:

Z. person \u003d 1000 ohm

The path is most dangerous through the heart, the brain, lungs. Characteristic paths: palm - feet, palm - palm, feet - feet. However, the deadly defeat is possible when the current passes on the path, which would seem to do not affect vital organs, for example, through the shin to the foot. This phenomenon is explained by the fact that the current in the body proceeds along the path of least resistance (nerves, blood), and not in a straight line - through fabrics with greater resistance (muscles, fat).

It has been established that the outcome of the lesion of the current depends on the physical and mental state man . If it is hungry, tired, inxicane or not healthy, then the probability of severe lesion increases. Women, teenagers, men with weak health are able to withstand significantly smaller currents (within b ma) than healthy men (12-15 mA).

The duration of exposure is one of the main factors affecting the outcome of the damage. The head cycle is approximately 1 s. The cycle has a phase T, Equal 0.1 s, when the heart muscle is relaxed and it is most vulnerable to current: fibrillation may occur. Than less than time The effects of current (less than 0.1 s), the less likelihood of fibrillation. Prolonged (a few seconds) The effect of the current leads to a severe outcome: the resistance of the body decreases, and the lesion current increases.

The mechanism of exposure to the electric current per person is complicated. On the one hand, in high-voltage installations there were cases when short-term (hundredths of a second) The effect of current into several amps did not lead to death. On the other hand, it was found that the deadly outcome is possible at a voltage of 12-36 V, when the current of several milliampers is affected. This occurs as a result of touching the current part the most vulnerable part of the body - the back of the palm, cheek, neck, shin, shoulder.

Considering the danger of electrical installations with voltage both to 1000, and above 1000 V, each working must remember that it is impossible to touch the current parts regardless of what voltage they are, it is impossible to close to the current parts in high-voltage installations, it is impossible to touch To metal designs of distribution devices, power lines supports, to the equipment enclosures that can be under voltage during circuit of the current-carrying parts.

Grinding to Earth in electrical installations is usually disconnected by the main relay protection for the split second. Therefore, electrical safety devices (grounding, etc.) is allowed to calculate, based on large values \u200b\u200bof the allowable current. In this case, the current is considered to be a current that does not cause fibrillation in 99.5% of experimental animals, the mass of the body and the heart of which is close to human. The permissible values \u200b\u200bof the current and voltages of the touch, obtained during laboratory studies, are shown in Table. 2.

From table. 3-2 It follows that currents of more than 65 mA and voltage of more than 65 V are allowed less than 1 s.