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Hostel for students :: Talks, lectures
Electric current and its impact on human
Electric current - is orderly movement of electric charges. The current in the part of the chain is directly proportional to the potential difference (ie, the voltage at the ends of the plot) and inversely proportional to the resistance of the circuit.
The nature and depth of the electric current on the human body depend on the strength and type of current, its time of action, path through the human body, physical and mental condition of the latter.
Threshold (tangible) is a current of about 1 mA. At a higher current one starts to feel unpleasant painful muscle contractions, and at a current of 12-15 mA no longer able to manage your muscular system and can not tear yourself from the power source. This current is called let go. Effect of the current in excess of 25 mA on muscle tissue leads to paralysis of the respiratory muscles and respiratory arrest. With a further increase in the current can occur fibrillation (twitching) of the heart. 100mA consider deadly.
Alternating current is more dangerous than standing. What matters is what parts of the body touch the electrical parts. The most dangerous are the ways in which the affected brain or spinal cord (head and arms, head - feet), heart and lungs (hands - feet).
Characteristic case falling under voltage is contact with one pole or phase current source. Stress acting at the same time per person, called contact voltage. Especially dangerous sites located at the temples, back, back of the hands, legs, head and neck.
Effects of electric current on the body is characterized by the main factors affecting:
1) electric shock, stimulating the body's muscles, resulting in convulsions, respiratory arrest and heart;
2) electrical burns resulting from heat generation during the passage of current through the human body. Depending on the parameters of the circuit and of the human condition can be redness, burns to form;
3) blistering or charring of tissue; occurs when the molten metal plating of the skin penetration of the metal pieces to it.
Effect of the current on the body is reduced to:
1) heat;
2) to electrolysis;
3) mechanical stress.
Mechanical action leads to the breakdown of tissues, bundle, shock action of liquid evaporation from the body tissues.
The action takes place in the thermal overheating and a functional disorder of the path of the current.
Electrolytic action of the current is expressed in the electrolysis of water in the tissues of the body, changing the composition of the blood.
In the presence of tissue changes in the electric current is applied dry aseptic bandage the affected part of the body.
To avoid electric shock, it is necessary to work with all electrical equipment and appliances carried out after disconnecting them from the circuit.
Means of protection against static electricity
Constant electrostatic field (ESP) - This field is fixed charges, the interaction between them.
Occurrence of static electricity occurs in the deformation and breakage (spraying) substances relative movement between the two bodies in contact, the layers of liquid and bulk materials, with vigorous stirring, crystallization, and also due to the induction.
Dielectrics in friction on the surface appear excessive charges, dry hands accumulate electrical charges that create the potential to 500 V. The potential difference between the thundercloud and Earth reaches enormous values measured by the hundreds of millions of volts, and in the air, a strong electric field.
Under favorable conditions, breakdown occurs. Charges tend to accumulate to a greater extent on the points or bodies, similar in form island.
Near these are sharper high electric fields. For this reason, lightning fall into the high-standing objects (towers, trees, etc.), and therefore dangerous to be a man in open space during a thunderstorm or near trees, metal objects.
Along with natural static electric fields in terms of the technosphere and household person is exposed to artificial static electric fields.
Artificial static electric fields due to the increasing use for the manufacture of household items:
1) toys;
2) shoes;
3) clothing;
4) for the interior decoration of residential and public buildings;
5) for the production of construction parts manufacturing equipment;
6) equipment;
7) tools;
8) of machine parts of various synthetic polymeric materials;
9) dielectrics.
Permissible levels of tension electrostatic fields set to GOST 12.1.045-84.
Application of the remedies work necessarily in cases where the actual levels of tension electrostatic fields in the workplace exceed 60 kV/m2.
When selecting ESD protection should be considered especially processes, physico-chemical properties of the material, indoor climate and another that defines a differentiated approach in the development of protective measures.
Common means of protection against static electricity are to reduce the generation of electrostatic charges or removal from the electrified material that is achieved by:
1) power metal and conductive elements of the equipment;
2) increasing the surface and bulk conductivity of dielectrics;
3) installation of static converters.
Grounding carried out independently of the use of other methods of protection.
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