Physiological effect of electric current
For an electric current to occur, it has to be conducted through a material. When the flow of electrons provided by electricity finds a resistance, it results in a dissipation of energy in the form of heat. If we have a certain amount of heat generated, the tissue may be burnt. Physiologically, the difference between a normal burn and a burn caused by electricity is that electricity has the ability to burn tissue beneath the skin, even burning internal organs without evidence of it
There are several effects produced on the human body by electric current such as pain, burns or even death. We must have in mind the safety rules when handling this type of devices since they around us every day.
Electrocution or so called electric shock occurs when current passes through the human body. The real measure of electrocution intensity is directly related to the amount of current (Ohms law),in amperes, that passes through the body, and not to the voltage. Resistance also plays a very important role on the amount of energy that passes through the body. Depending on the body resistance, wet (500Ω)or dry (1000Ω) and point of contacts we have very different effects for the same current.
General effects of electric current
The general effects of electric current differ for man, woman and child. For the same amount of current, women generally have worse symptoms then men. In the case of child or babies normally there is a distinct dark mark, similar to a burn on the lips, once that in the first years of life babies use the mouth to discover the world around them.
|Electric current (contact for 1s)||Effect|
|Below 1 mA||Not perceptible|
|1 mA||Threshold of feeling, tingling|
|5 mA||Slight shock. Not painful. Average individual can let go. Involuntary reaction can lead to indirect injuries|
|6-25 mA (women)||Painful shocks. Loss of muscle control|
|9 to 30 mA (men)||Freezing current, "can't let go". The person may be thrown away from the power source. Individual cannot let go. Strong involuntary reaction can lead to involuntary injuries|
|50 to 150 mA||Extreme pain. Respiratory arrest. Muscles reactions. Possible Death.|
|1 to 4.3 A||Fibrillation of the heart. Muscular contraction and nerve damage occur. Likely death.|
|10 A||Cardiac arrest, severe burns. Death is probable|
Electricity in the Nervous System
One of the most significant physiological effects of electricity regards the nervous system. Electricity can affect all the network of nerve cells and neurons which process and conduct the signals responsible for the regulation of our body functions. The sensory and motor organs of our body such as the brain and the spinal cord work together to allow it to move, answer, think, sense and remember. Nerve cells communicate by creating electrical signals with very small voltages. If electric current of sufficient magnitude passes through the living tissues, its effect will be override the natural impulses of the neurons, overloading the nervous system and blocking the passage of voluntary impulses that activate in the muscles. The muscles will then involuntarily contract (tetany).
Different effects of AC and DC
The effects of AC (alternating current) depends largely on frequency, low frequency tends to be much more dangerous than high frequency. AC with the same amperage and voltage as DC is more dangerous and provoke worse effects on the human body. Low frequency AC provokes muscle contraction (tetany) which can induce the "cannot let go" effect by freezing the muscles of the hand. This happens because the flexors of the hand are more strong than the extensors, so when an external electric estimation is applied the muscles flexors of the hand win. AC has more tendency to induce heart fibrillation while DC makes the heart stand still. That is why defibrillation equipment is DC, which stops the heart and gives a chance to recover.
The human body has is own resistance to electric current, 99% os this resistance is at the skin. As referred anteriorly dry and wet skin have much different values of resistance but are not the only aspect to have in account in electrocution. Cuts and deep abrasions of the skin contribute to a significant decrease on the skin resistance. Skin act as a capacitor and permits more current to flow if a voltage is changing rapidly. Skin breaks down from 500 V onwards which results has a decrease of the body's resistance that can mean a bigger amount of current entering the body, damaging the nerves and muscles. This is one of the reasons why sometimes there isn't significant damage of the skin but a significant deep tissue injury.