Physiological effects of electricity

Current (I) or Voltage (U): what is more dangerous?

These are the two definitions:

  • I: electrical current (A; ampere) : the amount of electrical charge transferred per unit time. It represents the flow of electrons through a conductive material. The SI unit of electrical current is the ampere, defined as 1 coulomb/second.
  • V: voltage ( V; volt) : potential difference between two different points. If a unit of electrical charge were placed in a location, the voltage indicates the potential energy of it at that point. In other words, it is a measurement of the energy contained within an electric field, or an electric circuit, at a given point. The SI unit of voltage is the volt, such that 1 volt = 1 joule/coulomb.

It is not really true that larger voltages are more dangerous than smaller ones. The danger to living things comes not from the potential difference, but rather the current flowing between two points.

Electric shock

Electric shocks caused by electrical equipment occur without warning and are often serious. The average worker is frequently involved in a dangerous electrical situation through not realising that voltages are as low as 32 V AC and 114 V dc can be just a lethal as much higher voltages.

Three factors determine the severity of the physiological effect of current on the human body.

  • The amount and kind of electrical current (DC, AC, Wave shape, Frequency and Direction of current flow)
  • The path the current follows in your body (hand to hand, hand to foot etc) - resistance of body
  • The duration of the electrical shock.

The following table represents the effects of an electrical current passing through an average human body.

The electric shock is even called electrocution. It occurs when current passes through the human body. The real measure of electrocution intensity is directly relay to the amount of current according to the Ohm's Law:

  • I= U/R

Resistance R 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. 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. Greater is the resistance of a body, smaller will be the current passes through it.

Probably you have experienced some form of electric “shock,” where electricity caused your body to experience pain or trauma. The fact you are reading this article means you were fortunate, the extent of that experience was probably limited to tingles or jolts of pain from static electricity buildup discharging through your body. If the electric shock persisted, the consequences was more serious. Why? We know that when a electric current is conducted through a material, any opposition to that flow of electrons (resistance) results in a dissipation of energy, usually in the form of heat. If the amount of heat generated is sufficient, the tissue may be burnt. The physiological effect is similar to the damage caused by an open flame or other high-temperature source of heat. Similar, but worse. Compared to a source of heat, these are the following further effects the electricity can cause:

  • it has the ability to burn tissue well beneath the skin of a victim, even burning internal organs.
  • it can effect our nervous system:
    • the body called “nerve cells” or “neurones” which process and conduct the multitude of signals responsible for regulation of many body functions.
    • the brain, spinal cord, and sensory/motor organs in the body function together to allow it to sense, move, respond, think, and remember.

Short and long term effects

If electric current of sufficient magnitude is conducted through a living creature, its effect will be to override the tiny electrical impulses normally generated by the neurons, overloading the nervous system and preventing both reflex and volition all signals from being able to actuate muscles. Muscles triggered by an external current will involuntarily contract. The point of contact can make a difference between death and life. What happens if the victim contacts an energized conductor with his or her hands? The forearm muscles responsible for bending fingers tend to be better developed than those muscles responsible for extending fingers, and so if both sets of muscles try to contract because of an electric current conducted through the person's arm, the fingers will clench into a fist. If the conductor delivering current to the victim faces the palm of his or her hand, this clenching action will force the hand to grasp the wire firmly, thus worsening the situation by securing excellent contact with the wire. The victim will be completely unable to let go of the wire.

This medical condition of involuntary muscle contraction is called tetanus. Electricians familiar with this effect of electric shock often refer to an immobilised victim of electric shock as being “froze on the circuit.” Shock-induced tetanus can only be interrupted by stopping the current through the victim.

What is the victim condition after the current is stopped? The victim may not regain voluntary control over their muscles for a while, as the neurotransmitter chemistry has been thrown into disarray. This principle has been applied in devices such as Tasers, which on the principle of momentarily shocking a victim with a high-voltage pulse delivered between two electrodes. A well-placed shock has the effect of temporarily immobilising the victim.


Electric current is able to affect more than just skeletal muscles in a shock victim, however. The diaphragm muscle controlling the lungs and the heart itself can also be “frozen” in a state of tetanus by electric current. Even currents too low to induce tetanus are could send the heart into a condition known as fibrillation. A fibrillating heart flutters rather than beats, and is ineffective at pumping blood to vital organs in the body. In any case, death from asphyxiation and/or cardiac arrest will surely result from a strong enough electric current through the body. Ironically, medical personnel use a strong jolt of electric current applied across the chest of a victim to “jump start” a fibrillating heart into a normal beating pattern.


How AC affects the body depends largely on frequency. Low-frequency (50- to 60-Hz) AC is used in US (60 Hz) and European (50 Hz) households; it can be more dangerous than high-frequency AC and is 3 to 5 times more dangerous than DC of the same voltage and amperage. Low-frequency AC produces extended muscle contraction (tetany), which may freeze the hand to the current's source, prolonging exposure. DC is most likely to cause a single convulsive contraction, which often forces the victim away from the current's source. AC's alternating nature has a greater tendency to throw the heart's pacemaker neurones into a condition of fibrillation, whereas DC tends to just make the heart stand still. Once the shock current is halted, a “frozen” heart has a better chance of regaining a normal beat pattern than a fibrillating heart. This is why “defibrillating” equipment used by emergency medics works: the jolt of current supplied by the defibrillator unit is DC, which halts fibrillation and gives the heart a chance to recover.

Effect of electrical current on human body

Below 1 mA Not perceptible
1 mA Threshold of feeling, tingling
5 mASlight 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 mAExtreme pain. Respiratory arrest. Muscles reactions. Possible Death.
1 to 4.3 AFibrillation of the heart. Muscular contraction and nerve damage occur. Likely death.
10 A Cardiac arrest, severe burst. Death is probable


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