At an early age, many of us were convinced by our own experience or learned from eyewitness accounts that, if you turn on the iron and try to cut the power cord, you will definitely experience painful hit. This is how electric current affects the body. At school, over the sockets they write: "220 V, dangerous, it will kill!" At substations, in transformer boxes and in other high-voltage installations, warning signs are posted: "Dangerous to life, high voltage!" So what exactly is a danger to humans and why? What hits: current or voltage? First, let's understand these concepts.
Content:
- Voltage conditions
- How does the current arise?
- Effects on the body
- Factors affecting the degree of damage
- Conclusion
Voltage conditions
Any substance consists of atoms with a positive nucleus and negatively charged electrons.
If, under the influence of external forces, a certain number of electrons are taken away from the atoms, then the resulting positive field will tend to return new negative particles to their place.
If electrons are not subtracted, but added, then the field will have a negative charge. This creates positive and negative potentials. When interacting between them, an attractive force arises. The greater the potential difference, the stronger the field and higher voltage is generated.
How does the current arise?
If, with the help of a conductor, the potentials of opposite charges are connected, then there will be a directed motion of charged particles, the so-called electricityseeking to eliminate the potential difference.
It is the directional movement of charged particles that makes our electrical appliances perform a useful action: shine, wash, heat, drill, and so on. The greater the potential difference, the higher the current. If the circuit is open, no current will flow, no matter how high the voltage.
Effects on the body
The human body, being a conductor, can complete an electrical circuit. Then a current will flow through the body, the strength of which is determined by the formula:
I = U / R, where:
- U is the magnitude of the voltage applied to a person;
- R - body resistance.
At this moment, the body is damaged.
The table shows which current is considered dangerous for humans:
- 15 mA, non-releasing value, self-release is not possible;
- 50 mA leads to cardiac fibrillation, respiratory arrest, death;
- 200 mA causes severe burns incompatible with life.
The shock occurs at voltages up to 1000 volts. Above this value, the lesion takes the form of burns.
Even without direct contact with high voltage equipment, a person can be fatally injured. So, when staying in dangerous proximity to a high-voltage installation, between the body and the conductive parts there is electric arcaccompanied by:
- a bright flash dangerous for eyes;
- instant heating of air up to 10,000-15,000 degrees Celsius;
- melting and evaporation of metals, the formation of aerosols.
The consequences of an arc discharge cause a burn injury to a person, incompatible with life.
It takes a tiny amount of time to trigger the protective automatics. But, when an arc occurs, a huge amount of energy is released, which kills a person in such a short time.
Factors affecting the degree of damage
DC shock is dangerous. But you can get rid of its influence without the help of outsiders at values from 20 to 25 mA.
More dangerous is the impact on the body of alternating current with a frequency of 50 - 500 Hz. A person can independently free himself from its influence only at very low values, ranging from 9 to 10 mA.
What is the current in a circuit depends on the voltage in this circuit and the resistance of all its elements, including the resistance of the human body. Dry skin has a higher resistance of approximately 100,000 ohms. Wet - only about 1000 ohms. The resistance of the internal organs is in the range of 500-1000 ohms.
If the stress applied to the body increases, the body's resistance decreases disproportionately. The same happens with an increase in the duration of exposure to electricity, as well as with a poor physical and mental state of a person.
It can be seen from the graph that if the voltage increases from 0 to 140 volts, the body resistance drops from 10,000 to 800 ohms. This non-linear relationship is reflected in the first curve. The second curve shows that the current passing through the human body, with increasing voltage, increases.
How severe the electric shock will be depends on the time it is exposed to the body. If the influence lasts for several seconds, the body's resistance decreases, and accordingly the current increases, which leads to serious consequences. If the exposure time is less than a tenth of a second, then the likelihood of cardiac fibrillation decreases, and the likelihood of survival increases.
It follows from the table that, for a favorable outcome, the duration of exposure to 65 mA at a calculated 65 V should not exceed 1 second.
I repeat that in the table of rated currents at different voltages of body resistance, it is taken as 1000 Ohm, in reality, it is impossible to predict the magnitude of the acting current, since the resistance of the body depends on the series factors.
The mechanism of the effect of electricity on the human body is complex. It happened when, in high-voltage installations, a short-term shock of several amperes did not lead to death. Whereas a voltage of 12-36 V and a current of several milliamperes were fatal to humans. The reason is damage caused by touching the conductors of the most vulnerable part of the body: neck, cheek, shoulder, back of the hand.
Conclusion
So what kills: current or voltage?
Since electric current is an ordered movement of charged particles, and voltage is one of characteristics of the electric field, under the influence of which this movement occurs, then we can assume that the voltage primary.
But the electric current kills, because it is he who flows through the human body, but he cannot flow through the body if the voltage is too low.
It turns out a pun - it kills the current, but without voltage, the current will not flow. Be careful not to check the "high voltage" label for correctness. And then you are not afraid of any blow, including an electric one.
We also recommend watching a video where the author clearly illustrates the topic of this article:
Related materials:
- What current is more dangerous for a person: direct or alternating
- First aid rules for electric shock
- What is the difference between phase voltage and linear
