The effects of an Electric Shock

The effects of electricity on the human body, whilst not always sufficient serious to cause death, can still have a long term adverse effect on a persons health and cause psychological effects. Perception of an electric shock can be different depending on the voltage, duration, current, path taken etc. An electric shock can also cause external burns due to resistance to current. Internal burns are caused by high voltage shocks from the source (>500V to 1000V). Neurological effects can also occur when current causes interference with nervous control, especially over the heart and lungs. Another serious effect of an electric shock is Ventricular Fibrillation. It can be induced when a current as low as 60mA travels through the chest for a fraction of a second. Fibrillations are usually lethal because all the heart muscle cells move independently. Above 200mA, the muscle contractions are so strong that the heart muscles cannot move at all.

Muscle spasms can occur and can cause a person to be unable to release from a current source; if there is sufficiently high current. The ‘let go’ current is the maximum current that can cause the flexor of the arm to contract but still allows a person to release their hand from the current source. The table below refers to adult people in good health at the time of the shock, but if the victim is a child or person in poor health, the effects can be more serious and the need for RCD protection is even greater.

The degree of risk depends not only on current, but also on time - the higher the current or the longer the time of shock, the greater the danger. In considering a 230V 50Hz AC supply, the following effects of current are typically observed.

Current 0 - 0.5mA

0.5 - 5mA 5mA - 10mA 10mA - 40mA Effect Generally this current is below the level of perception, resulting in no reaction.

Although no dangerous physiological effects, this current may produce a startle effect that results in injury due to falling etc.

Same effect as above but in addition muscular reaction may cause inability to let go of equipment. Once current flow ceases letting go is then possible.

Severe pain and shock as current value increases. At currents over 20mA the victim may experience breathing difficulties with asphyxia if current flow is uninterrupted. Reversible disturbance to heart rhythm and even cardiac arrest is possible at higher values of current and time.

40mA - 250mA

Severe shock and possibility of non-reversible disturbance to the normal cardiac cycle, referred to as Ventricular Fibrillation. The possibility of Ventricular Fibrillation increases as current and time increase. It is also possible to experience heavy burns at higher currents in addition to full cardiac arrest.

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