Which electric current loops are the most dangerous. The paths of electric current through the human body. The most dangerous path. What is safety shutdown

In practice, it has been established that the path of current passage through the human body plays a significant role in the outcome of the lesion. So, if vital organs - the heart, lungs, brain - are in the path of the current, then the danger of injury is very high, since the current acts directly on them.

If the current passes through other paths, then its effect can only be reflexive and not direct.

There are many possible current paths through the human body, also called current loops. The most common current loops are given in table. 1 .

Table 1

Characteristics of the most common paths of electric current through the human body*

* The table shows data on a person being injured by electric current, which caused loss of ability to work, i.e. leading to the accident.

The most dangerous are the loops: head - arms and head - legs, when an electrical current can pass through the brain and spinal cord. Fortunately, these loops occur relatively rarely.

Next most dangerous is the way right hand - legs, which ranks second in frequency.

Least dangerous is the way leg - leg, which is called the lower loop and occurs when a person is exposed to the so-called step tension.

3. The effect of electric current on a person

Electric current, passing through the human body, has thermal, chemical, biological and mechanical effects on his body.

Thermal– leads to dangerous heating of tissues and the occurrence of injuries such as burns, electrical marks, metallization of the skin.

Chemical– leads to electrolysis of blood and other solutions contained in the body, changes in their chemical composition, and disruption of their physiological functions.

Biological– is expressed in irritation of living tissues of the body, sharp, involuntary convulsive muscle contractions, reflex excitation of the nervous system and disruption of internal bioelectric processes.

The variety of effects of electric current on the human body often leads to various electrical injuries, which can be reduced to two types: local damage to the body and general electrical injuries - the so-called electric shock, when the entire body is affected due to disruption of the normal functioning of vital organs and systems. It has been established that the most vulnerable organ of the human body when electric current passes through it is the heart (Table 2).

Local electrical injuries include:

two types of electrical burns– current (contact) and arc. There are four degrees of burns: Ι – redness of the skin; ΙΙ – formation of bubbles; ΙΙΙ – necrosis of the entire thickness of the skin; ΙV – charring of tissues. Currents occur at a voltage no higher than 1–2 kV and in most cases are 1st and 2nd degree burns. Arcs between the current-carrying part and the human body (an arc with very high energy and a temperature above 3500 o C) cause severe burns of ΙΙΙ and ΙV degrees;

electrical signs- clearly defined spots of gray or pale yellow color on the surface of human skin exposed to current. Signs can also be in the form of scratches, wounds, cuts or bruises, warts, bleeding into the skin and calluses;

electroophthalmia– eye damage caused by intense radiation from an electric arc, the spectrum of which contains ultraviolet and infrared rays harmful to the eyes;

mechanical damage– arise as a result of sharp involuntary convulsive muscle contractions under the influence of current passing through the human body; As a result, ruptures of the skin, blood vessels and nerve tissues, as well as dislocations of joints and even bone fractures can occur.

Electric shocks (excitation of living tissues of the body by an electric current passing through it, accompanied by involuntary convulsive muscle contractions), depending on the outcome of the impact of the current on the body, come in four degrees:

Ι degree– convulsive muscle contraction without loss of consciousness;

ΙΙ degree- convulsive muscle contraction, loss of consciousness, but preservation of breathing and heart function;

ΙΙΙ degree– loss of consciousness and impaired cardiac activity and/or breathing;

ΙV degree– clinical death, i.e. lack of breathing and blood circulation.

D

table 2

When investigating accidents involving electrical current, the first step is to determine which path the current took. A person can touch live parts (or non-live metal parts that may be energized) with a variety of different parts of the body. Hence the variety of possible current paths.

The following are considered most likely:

“right arm - legs” (20% of cases of lesion);

“left arm - legs” (17%);

“both hands and feet” (12%);

“head - legs” (5%);

“hand - hand” (40%);

“leg - leg” (6%).

All loops, except the last one, are called “large” or “full” loops; the current covers the heart area and they are the most dangerous. In these cases, 8-12 percent of the total current flows through the heart. The leg-to-leg loop is called “small”; only 0.4 percent of the total current flows through the heart. This loop occurs when a person finds himself in the current spreading zone, coming under step voltage.

Stepper is called the voltage between two points on the ground, caused by the spreading of current in the ground, while simultaneously touching them with a person’s feet. Moreover, the wider the step, the greater the current flows through the legs.

This current path does not pose a direct danger to life, but under its influence a person may fall and the current path will become life-threatening.

To protect against step voltage, additional protective equipment is used - dielectric boots, dielectric mats. In cases where the use of these means is not possible, you should leave the spreading area so that the distance between your feet standing on the ground is minimal - in short steps. It is also safe to move on dry boards and other dry, non-conductive objects.

1. Electrical safety in existing electrical installations up to 1000 Volts. Manufacturing jobs.

Electrical installations are those installations in which electricity is produced, converted and consumed. Electrical installations include mobile and stationary power sources, electrical networks, switchgear and connected current collectors.

Existing electrical installations installations are considered to be those that are fully or partially energized or to which voltage can be applied at any time by turning on the switching equipment.

According to the degree of danger of electric shock to personnel, electrical installations are divided into electrical installations up to 1000 Volts And above 1000 Volts .

An employee of management personnel with an electrical safety group of at least 4 has the right to give orders to carry out work in existing electrical installations up to 1000 Volts.

Work in electrical installations with regard to safety measures is divided into:

with stress relief;

without relieving voltage on live parts and near them.

TO work with stress relief refers to work performed in an electrical installation (or part of it) in which voltage is removed from live parts.

TO work without relieving voltage on live parts and near them include work performed directly on these parts or near them. In installations with voltages above 1000 Volts, as well as on overhead lines up to 1000 Volts, the same work includes those that are performed at distances from live parts that are less than permissible. Such work must be performed by at least two persons: the person performing the work with group no lower than IV, the rest – lower than III.

Sometimes you have to transmit a signal over a long distance (tens of meters, or even kilometers). The main problem with this is that an electromagnetic wave (interference) can rush through the line and try to induce a current in it. The current will be negligible, but since the inputs are usually high-impedance, hundreds of kilo-ohms, even such minor interference may cause overvoltage at the input. After all, according to Ohm’s law, U = I * R. We can have an input R under GigaOhm, while inducing a current of even 0.001 mA can pump the voltage up to a kilovolt. The entrance will blow away a sweet soul, although the energy there is not great, but how much does the thin-film gate of a transistor need? There is only one solution - to reduce the input impedance.

A good way to solve this problem is to change the signal from voltage to current. Those. For levels we take not the presence of any voltages, but the current values ​​in the circuit. It will be more difficult to induce interference here, because the two wires of the line run in parallel, which means the interference will be induced into them simultaneously and cancel itself, being subtracted at the differential input of the receiver.

We will inject current into the line using a current source, which pleases us with the fact that it doesn’t care what resistance the line has, it will provide the given current as long as there is enough power.

Digital line
Everything is simple here, usually RS232 and similar interfaces with independent channels for reception/transmission are decoupled via a current loop.
The advantage of the current loop is that it is easily decoupled by optics, because the LED, which is the main transmitter of the optocoupler, is powered by current.

The diagram might look like this:


When we apply a unit to the input, it lights up the LED, the optocoupler transistor opens and lets current into the loop. This current lights up the LED in the second optocoupler, its transistor opens and presses the line to ground. In this case, the line turns out to be inverted. But if desired, this can easily be solved with one transistor.

Here you can choose something like SFH610A as an optocoupler

. The main thing is that the maximum voltage that the transistor can withstand is higher than the current source can develop, because it will try to push through the transistor when it is closed. For this optocoupler this is Vceo = 70V. Typically, the source voltage rarely exceeds 24 volts. You should also look at the collector current for the optocoupler so that it is no less than what the current source produces. For this optocoupler it is 50mA.

If we also take an external power source for the line, then the circuit turns out to be completely indestructible. Because The receiver, transmitter and line are not connected to each other at all.

As a current source, I usually plug it in here NSI45020. In general, this is a linear LED driver. The figurine is the size of a 1206 resistor and has a strictly specified current at the output - 20mA.

You can roll in the supply voltage up to 45 volts, you can parallel it so that the current is higher. At a price of 5 rubles, the piece is a very cool thing. I recommend keeping it on the farm.

And for conservatives, the LM317 in current stabilizer mode has not yet been canceled. The truth is much more cumbersome and usually costs more. But you can get it without any problems at any radio stall.

The disadvantage of optical isolation is the speed limitation. Optocouplers, especially consumer-grade ones, have very mediocre frequency characteristics. But for some UART it will be enough. The speed is also affected by the fact that a long line has a large capacity, and it is charged by a current source, i.e. the further you go, the greater the line capacity and the slower the transmission.

Analogue line

What if you need to extract data from some remote analog sensor? Here, too, a current loop will come to the rescue, although the design will be somewhat more complicated.

We will need to make a source that converts voltage into current. With a linear dependence, let’s say we injected 5 volts into the input, and our circuit injected 50mA into the line. This is done using an operational amplifier. Approximately like this:

It works simply. Because An op-amp covered by feedback tends to equalize its inputs, i.e. the voltage between the direct and inverse input is zero, then we can assume that Uin is connected directly to R0. And the current through R0 turns out to be equal to Uin/R0. After all, the resistance of the op-amp inputs is VERY large, so large that we can safely assume that no current flows there. And since R0 is part of the loop, the current in the loop will be equal to the current R0, regardless of the line resistance and load resistance, of course, if the power source can push through these resistances, and the transistor does not go into saturation, remaining in linear mode. As a power source, you can take an independent stabilized source, 12 volts.

On the other side of the loop, it is enough to remove the voltage drop across the load resistor Rн.

Here, for the sake of the lulz, I assembled this design on the Pinboard II layout field. Because The setting resistor R0 turned out to be 10 kOhm (it’s located next to the layout field), then the voltage/current ratio turned out to be 1:10000, i.e. For every 1 volt there is 0.1mA in the loop. It's not a standard, and in general it's too little, but the principle of operation shows well.

And video of the work:

There is a more cumbersome, but also much more accurate way:


Here we install a special measuring resistor Rs and use an op-amp to measure the drop, and then put the result into the second op-amp. Because the design from OP1 is feedback for OP2, and it outputs the difference at its inputs to zero, then we get that:

Uin = R2/R1*Is*Rs
At
R2 = 10k
R1 = 1k
Rs = 10

We get the dependence Is = Uin/100 with good linearity, especially if we take precision amplifiers with Rail-2-Rali output.

If you need maximum accuracy, then it is better to use a ready-made microcircuit. There are also a lot of specialized current loop shapers. For example MAX15500. You turn it on according to the datasheet and rejoice :)

Galvanic isolation of the analog current loop can be done using isolating amplifiers. Like ISO124

Its gain factor is 1. That is 1 volt in - 1 out. No hassles with feedback or anything like that. Two independent power inputs, on one side and the other. One drawback is that it is not cheap. The same ISO124 from 15 bucks apiece.

Another cool thing about a current loop is that you can power a remote device through the same loop. Because the current source compensates for consumption. Of course, within reasonable limits, but for some remote sensors it’s quite a good option.

Standards
There is no single standard for the current loop, current values ​​and connectors, such as with RS232. But the industry has more or less established a standard for an analog current loop of 4...20mA, i.e. the minimum level is 4mA, and the maximum is 20mA. Zero current is considered a line break. For a digital loop, the range 0...20mA is most often used. Also sometimes there is a 0...60mA option, but this is exotic.

The most important condition for electric shock to a person is the path of this current. If vital organs (heart, lungs, brain) are in the way, then the danger of fatal damage is very high. If the current passes through other paths, then its effect on vital organs can only be reflexive. At the same time, although the danger of fatal injury remains, its likelihood is sharply reduced.

Current flows only in a closed circuit. Therefore, there is both an entry point of the human body and an exit point of the electric current. There are an innumerable number of possible current paths in the human body. However, the following can be considered typical:

hand leg; hand-hand; leg-leg; head-hand; leg-head, etc.

The degree of danger of various current loops can be assessed by the relative number of cases of loss of consciousness, as well as by the value of the current passing through the heart region.

The most dangerous are the “head-arm” and “head-leg” loops, when the current can pass not only through the heart, but also through the brain and spinal cord.

Ticket No. 14

In terms of ensuring reliability, which electrical receivers belong to the second category of electrical receivers, permissible interruptions in power supply?

PUE (clause 1.2.18-1.2.21)

Category II power receivers are power receivers whose power supply interruption leads to massive under-supply of products, massive downtime of workers, machinery and industrial transport, disruption of the normal activities of a significant number of urban and rural residents;

For category II electrical receivers, in the event of a power failure from one of the power sources, interruptions in power supply are allowed for the time required to turn on the backup power by the actions of the duty personnel or the mobile operational team.

What are workers who repair electrical installations personally responsible for?

PTEEP clause 1.2.9

For disruptions in the operation of electrical installations, the following persons bear personal responsibility: workers carrying out equipment repairs - for disruptions in operation caused by poor quality of repairs.

Frequency of testing knowledge of administrative and technical personnel.

PTEEP clause 1.4.20-1.4.21

1.4.20. The next inspection should be carried out within the following periods:

• for electrical personnel directly organizing and carrying out work on servicing existing electrical installations or performing adjustment, electrical installation, repair work or preventive tests in them, as well as for personnel who have the right to issue orders, orders, and conduct operational negotiations - once a year;
• for administrative and technical personnel not belonging to the previous group, as well as for labor protection specialists authorized to inspect electrical installations - once every 3 years.

1.4.21. The time of the next test is set in accordance with the date of the last knowledge test.

4. What is meant by order? Its validity period, registration procedure.

POTEE (clause 7.1-7.7)

An order is a written assignment for the performance of work, defining its content, place, time, safety measures (if required) and the workers entrusted with its implementation, specifying the electrical safety group.

The order is of a one-time nature, its validity period is determined by the length of the working day or shift of executors.

If it is necessary to continue work, if working conditions or the composition of the team changes, the order must be given again.

In case of breaks in work within one day, re-admission is carried out by the work manufacturer.

7.2. The order is given to the contractor and the permitter. In electrical installations that do not have local operating personnel, in cases where permission to work at the workplace is not required, the order is given directly to the employee performing the work.

7.4. An order may be issued for work in turn on several electrical installations (connections).

7.5. Admission to work under orders must be documented in the work log for work orders and orders.

Electrical injury. Cold injury.

Indicate what types of damage are observed when the body is exposed to electric current?

1. $Mechanical

2. Electrochemical

3. $Thermal

4. $Radiation

5. $General biological

%Answer: 1,2,3,5

#2. For the first degree of electric shock it is typical:

4. $Clinical death

#3. Stage II electric shock is characterized by:

1. Convulsive muscle contraction without loss of consciousness

2. Convulsive muscle contraction with loss of consciousness, but with preserved breathing and cardiac function

3. Loss of consciousness and disturbances in cardiac activity or breathing (or both)

4. $Clinical death

#4. III degree of electric shock is characterized by:

1. Convulsive muscle contraction without loss of consciousness

2. Convulsive muscle contraction with loss of consciousness, but with preserved breathing and cardiac function

3. Loss of consciousness and disturbances in cardiac activity or breathing (or both)

4. $Clinical death

#5. IV degree of electric shock is characterized by:

1. Convulsive muscle contraction without loss of consciousness

2. Convulsive muscle contraction with loss of consciousness, but with preserved breathing and cardiac function

3. Loss of consciousness and disturbances in cardiac activity or breathing (or both)

4. $Clinical death

#6. A feature of electrical injury is:

1. $Tissue damage along the entire path of electricity

2. Depression of the central nervous system, respiratory and cardiovascular systems

3. Local injuries predominate (muscle ruptures, tendons, bone fractures)

%Answer: 1.2

#7. The severity of electric shock depends on:

1. $Amperage

2. Mainly due to voltage

3. Type of current, duration of action

4. Current paths

%Answer: 1,3,4

#8. What type of electric current is the most dangerous:

1. $DC

2. $Alternating current

3. $Danger is proportional only to the magnitude of the current

#9. The peculiarity of the biological effect of electric current is:

1. $Skeletal and smooth muscle paralysis

2. $Stimulation of skeletal and smooth muscles

3. $Tonic convulsions

4. $Clonic seizures

%Answer: 2.3

#10. When providing first aid during an electric shock, you must:

1. Applying aseptic dressings to wound surfaces

2. $Break the electrical circuit

3. $Artificial ventilation and chest compressions

4. $Introduce respiratory analeptics

5. $Cardiac defibrillation

%Answer: 2,3,5

#eleven. Specify the features of electrical burns:

1. Electrical burns are always I-IIIa degrees

2. Electrical burns are always IIIb-IV degrees

3. Electrical burns are painless

4. $Severe pain syndrome is noted in the area of ​​the electrical burn.

5. $Progression of necrosis due to vascular thrombosis is noted

6. Tissue necrosis is always superficial

7. $Lack of demarcation for a long time

8. $There is a clear boundary between the healthy and the affected part

%Answer: 2,3,5,8

#12. Surgical treatment of electrical burns is characterized by:

1. Waiting and waiting

2. $Early necrotomy, necrectomy

3. $No different from methods of treating thermal burns

4. Possible preventive ligation of adjacent vessels

5. Early closure of skin defects

%Answer: 2,4,5

What is a "current loop"?

1. Variant of current propagation in the body

2. Current input location

3. Current output location

4. Electrochemical reactions in the body

#14. The most dangerous “current loops” passing through:

1. $Upper limbs

2. $Heart

3. Lower limbs

4. Central nervous system

%Answer: 2.4

#15. Acute cold injury includes:

2. $chill

3. Cold neurovasculitis

4. $Frostbite

%Answer: 1.4

#16. Chronic cold injury includes:

1. Freezing (general cooling)

2. $chill

3. Cold neurovasculitis

4. $Frostbite

%Answer: 2.3

#17. Indicate the degree of frostbite according to the depth of the lesion:

2. $Ia, Ib, II, III, IV

3. $I, II, III, IV

4. $I, II, IIIa, IIIb, IV

#18. Indicate the degree of frostbite classified as superficial:

1. $I degree

2. $II degree

3. $III degree

4. $IV degree

%Answer: 1.2

#19. Indicate what degree of frostbite is considered deep:

1. $I degree

2. $II degree

3. $III degree

4. $IV degree

%Answer: 3.4

#20. Frostbite of the first degree is characterized by:

5. $Death of the entire thickness of the skin

#21. Frostbite of the second degree is characterized by:

1. $Bubbles with transparent content

2. Necrosis of the entire thickness of the skin and underlying tissues (subcutaneous tissue, muscles, tendons, bones)

3. Bubbles with hemorrhagic contents

4. Necrosis of the horny, granular, and partially papillary layers of the epithelium

5. $Death of the entire thickness of the skin

6. Circulatory disorder without necrotic tissue changes (hyperemia and edema)

%Answer: 1.4

#22. III degree frostbite is characterized by:

1. $Bubbles with transparent content

2. Necrosis of the entire thickness of the skin and underlying tissues (subcutaneous tissue, muscles, tendons, bones)

3. Bubbles with hemorrhagic contents

4. Necrosis of the horny, granular, and partially papillary layers of the epithelium

5. $Death of the entire thickness of the skin

6. Circulatory disorder without necrotic tissue changes (hyperemia and edema)

%Answer: 3.5

#23. IV degree frostbite is characterized by:

1. $Bubbles with transparent content

2. Necrosis of the entire thickness of the skin and underlying tissues (subcutaneous tissue, muscles, tendons, bones)

3. Bubbles with hemorrhagic contents

4. Necrosis of the horny, granular, and partially papillary layers of the epithelium

5. $Death of the entire thickness of the skin

6. Circulatory disorder without necrotic tissue changes (hyperemia and edema)

#24. The main causes of frostbite include:

1. Low ambient temperature

2. High humidity and wind speed

3. $Alcohol intoxication

4. Vascular diseases of the extremities

5. Previously suffered frostbite

%Answer: 1.2

#25. Common factors contributing to frostbite include:

1. $Overwork and exhaustion

2. High humidity, high wind speed

3. $Alcohol intoxication

4. $Hypo- and adynamia

5. Previously suffered frostbite

6. $Loss of consciousness

%Answer: 1,3,4,6

#26. Local factors contributing to frostbite include:

1. $Vascular diseases of the extremities

2. Previously suffered frostbite

3. Limb injuries

4. $Tight shoes

5. $Loss of consciousness

6. $Hypo- and adynamia

%Answer: 1,2,3,4

#27. Specify periods of frostbite:

1. $Pre-reactive

2. $Reactive

3. $Erectile