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close this bookHow to Act after Accidents caused by Electrical Current - Course: Basic skills and knowledge of electrical engineering. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 20 p.)
View the document(introduction...)
View the documentIntroduction
View the document1. Effects of Electric Current on Human Organism
View the document2. Rescue of Injured People out of Electric Plants below 1 kV
Open this folder and view contents3. Immediate Measures after an Accident Caused by Electric Current
Open this folder and view contents4. Giving Artificial Respiration to Injured People
View the document5. Measures Taken in the Case of Circulatory Arrest
View the document6. Hints for the Transportation of Injured People

1. Effects of Electric Current on Human Organism

Irritating effect

- If an electric current flows through the human body, the entire sensitive muscular system becomes cramped.

- For the degree of injury caused by electric current two factors are decisive:

· The intensity of current
· The duration of current flow through the body.

- From the equation I = U/R is to be seen that the current intensity depends on the following values:

· Intensity of the voltage affecting a person;
· Resistance of the parts of the human body through which the current flows.

Influence of the current intensity on the sensations with alternating current with 50 Hz supposing a current path hand-body-feet.

Current intensity
I in mA

Sensations

3.5

Current just perceptible on the palms (absolute threshold).

5

Prickling sensation in the whole hand as if it went to sleep.

8

Pressure in the forearm.

10

First sensations at the soles of the feet.

11.5

Slight cramping of the wrist, moving of the hand is difficult, pressure on the heels.

12.5

Prickling in the upper arm, severe cramping of the entire arm,


especially of the wrist.

14.5

Strong prickling along the arm to the armpit, forearm almost numb up to the elbow, letting loose "still" possible.

15.8

Pressure in ankles and heels, thumb of the hand completely cramped.

18

Letting loose only possible "with greatest effort".

20

Shooting pain in the wrist-joint and elbow.


"Letting loose no more possible!"


"Danger of life!"

more than 40

"Absolute danger of life! Death may occur."

- For the protection of man, the highest permissible contact voltage is:

· for alternating current voltage 50 V,
· for direct current voltage 120 V.

- The body resistance is varying and different with each person.

- The resistance of the body is, to a far exent, determined by the resistance of the skin.

· Dry skin offers a resistance of some kiloohms.
· Sweaty skin has a resistance of a few ohms only.

Approximate figures of the body resistance

Current path

Resistance

Hand-body-hand

approx. 1300 ohms

Hand-body-feet

approx. 1000 ohms

Hands-body-feet

approx. 650 ohms

Foot-foot

approx. 1300 ohms

What is the intensity of a current flowing through a person, if the current path is hand-feet and the applied voltage 220 V?
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What conclusions have to be drawn from this current intensity?
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- The most dangerous irritating effect of the three-phase current is the "ventricular fibrillation". This can occur if the current flows during the T-spike of the electrocardiogram.

The frequency of the three-phase current disturbs the heart rhythm so that it comes to the ventricular fibrillation. This means that the heart works at 400 to 1000 contractions per minute and no blood is pumped through the body.

Why is each minute of first aid decisive in the case of an accident caused by electric current?
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Thermal effect

- By the electric arc, i.e. the thermal effect of the electric current, clothes may catch fire and the skin be burned.

Fire with burning people must only be smothered with the help of insulating material, such as ' blankets or clothes. Do never extinguish the fire by water!