<P> The injury related to electric shock depends on the magnitude of the current . Very small currents may be imperceptible or produce a light tingling sensation . A shock caused by low current that would normally be harmless could startle an individual and cause injury due to suddenly jerking away from the source of electricity, resulting in one striking a stationary object, dropping an object being held or falling . Stronger currents may cause some degree of discomfort or pain, while more intense currents may induce involuntary muscle contractions, preventing the victim from breaking free of the source of electricity . Still larger currents usually result in tissue damage and may trigger fibrillation of the heart or cardiac arrest, any of which may ultimately be fatal . If death results from an electric shock the cause of death is generally referred to as electrocution . </P> <P> Heating due to resistance can cause extensive and deep burns . Voltage levels of 500 to 1000 volts tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage divided by resistance) available from the source . Damage due to current is through tissue heating . For most cases of high - energy electrical trauma, the Joule heating in the deeper tissues along the extremity will reach damaging temperatures in a few seconds . </P> <P> A domestic power supply voltage (110 or 230 V), 50 or 60 Hz alternating current (AC) through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 30 mA . With direct current (DC), 300 to 500 mA is required . If the current has a direct pathway to the heart (e.g., via a cardiac catheter or other kind of electrode), a much lower current of less than 1 mA (AC or DC) can cause fibrillation . If not immediately treated by defibrillation, fibrillation is usually lethal because all of the heart muscle fibres move independently instead of in the coordinated pulses needed to pump blood and maintain circulation . Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all, but these conditions prevent fibrillation . </P> <P> Current can cause interference with nervous control, especially over the heart and lungs . Repeated or severe electric shock which does not lead to death has been shown to cause neuropathy . Recent research has found that functional differences in neural activation during spatial working memory and implicit learning oculomotor tasks have been identified in electrical shock victims . </P>

The minimum frequency required to cause a current to flow