Not always, but only when handled carelessly. Shock induced muscle tetany is the most important effect of current on the muscles. If a person touches the energized conductor, fore arm muscles contracts forcefully and fingers bend. So the person involuntarily holds the conductor. Therefore the victim will be unable to take the hand from the conductor.
As you know, electricity is the flow of electrons through a conductor from its source to the destination. If the conductor offers less resistance, the flow current will be fast and if the conductor has some resistance, the flow of electrons will be obstructed leading to slow movements which generate heat through friction.
Human skin is a semiconductor for electricity and current passes through the body to the ground just like the flow of current through the electric wire. This flow of current causes burning and shock. If the skin resistance is low, the chance of shock hazard is very high. Some people are more sensitive to current while others are less sensitive. Electrical safety measures are necessary while dealing with high voltage AC available from the power grid. Ignorance can lead to a fatal shock or fire hazards.
Remember, Electricity travels at the speed of light. Its flow is around 299,460 kilo meters per second so you will not get time to react because you can’t move faster than electricity. So the best way is staying out of its way.
The amount of current passing through the body is equal to the voltage applied between two points of the body divided by the resistance between the points. If the resistance is more, less electrons pass between the points. The resistance of the human body is not a fixed value and it varies from person to person and from time to time depending on the physiological states.
Body offers less resistance in high emotional state and high resistance in calm state. Body resistance to electricity also depends on the fat content and the quantity of ions especially that of sodium chloride in the blood. Sweating increases the electrical conductivity since sweat contains salts. Approximately 1 Meg ohm resistance appears across the body between two hands. This may drops to few Kilo ohms in various physiological conditions.
Effect of current on the body
Let us see how current becomes harmful to Human body. Individual body chemistry has significant impact on the effect of current on the body. Some people are more sensitive to current while others are less sensitive. The table below indicates the effect of AC and DC on the human body.
AC DC Effect
0.3-0.4 mA 0.6-1 mA Slight sensation
0.7-1 mA 40-60 mA Pain feeling
10-15 mA 50-70 mA Voluntary contraction. Cannot withdraw hands
15 – 20 mA 60-100 mA Difficulty in breathing. Pain
100 mA 500 mA Heart fibrillation
It is important to note that a low AC current of 15-20 mA across the chest can induce heart fibrillation in some physiological conditions. Ohms law can be used to determine the amount of voltage required to pass 20 mA current through the body. I x R = V.
If the skin resistance of the dry body is 1 M and current is 20 mA then 20 mA x 1 Meg ohms is 20, 000 volts or 20kV.The condition worsens if the body is wet. Skin resistance drops to 20 K or less when the body wet. In this state the voltage required to cause 20 mA current to pass through the body is
20mA x 20K = 400 volts.
If the body has metal objects or in contact with a metal object, the skin resistance drops to 1 K or less. In this condition only 20 volt is sufficient to pass 20 mA current through the chest. A current around 17-20 mA is enough to cause heart fibrillation. In short, the effect of current worsens if the body is wet or in contact with a metal object.
1. Effect on the Skin
Human skin act like a conductor and offers resistance to oppose the flow of electrons. This opposition effect causes dissipation of energy leading to the generation of heat. Electricity has the ability to burn skin and underlying tissues and organs.
2. Effect on the Nervous system
Nervous system is composed on electrically active nerve cells which carry minute current and voltage generated from the cells itself to conduct impulses. If an electric current of sufficient magnitude passes through the nerves, it overrides the small signals of the nerves leading to the involuntary contractions of the muscle.
3. Effect on the Muscle
Shock induced muscle tetany is the most important effect of current on the muscles. If a person touches the energized conductor, forearm muscles contracts forcefully and fingers bend. So the person involuntarily holds the conductor. So that the victim will be unable to take the hand from the conductor. Shock induced tetanus can be removed only if the current flowing through the victim is stopped.
4. Effect on the internal organs
Internal organs such as Diaphragm, Lungs, Heart etc are also can be frozen due to the flow of current. Human heart is most susceptible to such current induced freezing. Heart has conducting fibers called SA node (Sinuatrial Node) and AV (Auriculoventricular) node for initiating heart beats by producing electric signals. These specialized tissues are called Pacemakers. When external current passes through the heart, the normal functioning of the pace makers will be affected leading to heart fibrillation and ineffective pumping of heart. External current can cause sudden contraction of lungs leading to Asphyxiation.