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An electric shock can occur upon contact of a human's body with any source of voltage high enough to cause sufficient current flow through the muscles or hair. The minimum current a human can feel is thought to be about 1 milliampere (mA). The current may cause tissue damage or fibrillation if it is sufficiently high. Death caused by an electric shock is referred to as electrocution.
Additional recommended knowledge
The perception of electric shock can be different depending on the voltage, duration, current, path taken, frequency, etc. Current entering the hand has a threshold of perception of about 5 to 10 mA (milliampere) for DC and about 1 to 10 mA for AC at 60 Hz. Shock perception declines with increasing frequency, ultimately disappearing at frequencies above 15-20 kHz.
Heating due to resistance can cause extensive and deep burns. Voltage levels of (> 500 to 1000 V) shocks tend to cause internal burns due to the large energy (which is proportional to the duration multiplied by the square of the voltage) available from the source. Damage due to current is through tissue heating. In some cases 16 volts might be fatal to a human being when the electricity passes through organs such as the heart.
A low-voltage (110 to 220 V), 50 or 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA. With 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. Fibrillations are usually lethal because all the heart muscle cells move independently. Above 200mA, muscle contractions are so strong that the heart muscles cannot move at all.
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.
When the current path is through the head, it appears that, with sufficient current, loss of consciousness almost always occurs swiftly. (This is borne out by some limited self-experimentation by early designers of the electric chair and by research from the field of animal husbandry, where electric stunning has been extensively studied) .
Approximately 80% of all injuries and fatalities caused by electrical incidents are not caused by electric shock, but by the intense heat, light, and pressure wave (blast) caused by electrical faults. The arc-flash in an electrical fault produces the same type of light radiation from which electric welders protect themselves using face shields with dark glass, heavy leather gloves, and full-coverage clothing. The heat produced may cause severe burns, especially on unprotected flesh. The blast produced by vaporizing metallic components can break bones and irreparably damage internal organs. The degree of hazard present at a particular location can be determined by a detailed analysis of the electrical system, and appropriate protection worn if the electrical work must be performed with the electricity on.
Issues affecting lethality
Other issues affecting lethality are frequency, which is an issue in causing cardiac arrest or muscular spasms, and pathway - if the current passes through the chest or head there is an increased chance of death. From a mains circuit the damage is more likely to be internal, leading to cardiac arrest.
The comparison between the dangers of alternating current and direct current has been a subject of debate ever since the War of Currents in the 1880s. DC tends to cause continuous muscular contractions that make the victim hold on to a live conductor, thereby increasing the risk of deep tissue burns. On the other hand, mains-frequency AC tends to interfere more with the heart's electrical pacemaker, leading to an increased risk of fibrillation. AC at higher frequencies holds a different mixture of hazards, such as RF burns and the possibility of tissue damage with no immediate sensation of pain. Generally, higher frequency AC current tends to run along the skin rather than penetrating and touching vital organs such as the heart. While there will be severe burn damage at higher voltages, it is normally not fatal.
It is sometimes suggested that human lethality is most common with alternating current at 100-250 volts, however death has occurred from supplies as low as 32 volts and supplies at over 250 volts frequently cause fatalities.
Electrical discharge from lightning tends to travel over the surface of the body causing burns and may cause respiratory arrest.
Lethality of a shock
The voltage necessary for electrocution depends on the current flowing through the body and the duration of the current flow. Using Ohm's law, Voltage = Current x Resistance, we see that the current drawn depends on the resistance of the body. The resistance of our skin varies from person to person and fluctuates between different times of day. In general, dry skin isn't a very good conductor having a resistance of around 10,000 Ω, while skin dampened by tap water or sweat has a resistance of around 1,000 Ω.
The capability of a conducting material to carry a current depends on its cross section, which is why males typically have a higher lethal current than females (10 amperes vs 9 amperes) due to a larger amount of tissue. However, death can occur from currents as low as 0.1 to 0.3 amps.
Using Ohm's law, we may derive the voltages lethal to the human body. This is given in the following table: 
Point of entry
Avoiding danger of shock
It is strongly recommended that people should not work on exposed live conductors if at all possible. If this is not possible then insulated gloves and tools should be used. If both hands make contact with surfaces or objects at different voltages, current can flow through the body from one hand to the other. This can lead the current to pass through the heart. Similarly, if the current passes from one hand to the feet, significant current will probably pass through the heart. An alternative to using insulated tools is to isolate the operator from ground, so that there is no conductive path from the live conductor, through the operator's body, to ground. This method is used for working on live high-voltage overhead power lines. 
It is possible to have a voltage potential between neutral wires and ground in the event of an improperly wired (disconnected) neutral, or if it is part of certain obsolete (and now illegal) switch circuits. The electrical appliance or lighting may provide some voltage drop, but not nearly enough to avoid a shock. "Live" neutral wires should be treated with the same respect as live wires. Also, the neutral wire must be insulated to the same degree as the live wire to avoid a short circuit.
Electrical codes in many parts of the world call for installing a residual-current device (RCD or GFCI, earth fault circuit interrupter) on electrical circuits thought to pose a particular hazard to reduce the risk of electrocution. In the USA, for example, a new or remodeled residential dwelling must have them installed in all kitchens, bathrooms, laundry rooms, garages, and any other room with an unfinished concrete floor such as a workshop. These devices work by detecting an imbalance between the live and neutral wires. In other words, if more current is passing through the live wire than is returning though its neutral wire, it assumes something is wrong and breaks the circuit in a fraction of a second. There is some concern that it might not be fast enough for infants and small children in rare instances.
The plumbing system in a home or other building has traditionally used metal pipes and thus been connected to ground through the pipes. This is no longer always true because of the extensive use of plastic PVC piping in recent years, but a plastic system cannot be relied upon for safety purposes. Contrary to popular belief, pure water is not a good conductor of electricity. However, most water is not pure and contains enough dissolved particles (salts) to greatly enhance its conductivity. When the human skin becomes wet, it allows much more current to flow than the dry human body would. Thus, being in the bath or shower will not only ground oneself to return path of the power mains, but lower the body's resistance as well. Under these circumstances, touching any metal switch or appliance that is connected to the power mains could result in electrocution. While such an appliance is not supposed to be live on its outer metal switch or frame, it may have become so if a defective live bare wire is accidentally touching it (either directly or indirectly via internal metal parts). It is for this reason that mains electrical sockets are prohibited in bathrooms in the UK. However, widespread use of plastic cases for everyday appliances (which won't conduct electricity), grounding of these appliances, and mandatory installation of Residual Current Devices (R.C.D.s) have greatly reduced this type of electrocution over the past few decades.
A properly earthed appliance eliminates the electric shock potential by causing a short circuit if any portion of the metal frame (chassis) is accidentally touching the live wire. This will cause the circuit breaker to turn off or the fuse to blow resulting in a power outage in that area of the home or building. Often there will be a large "bang" and possibly smoke which could easily scare anyone nearby. However, this is still much safer than risking electric shock, as the chance of an out-of-control fire is remote. Many people in this situation have nevertheless called the fire department as a precaution.
Where live circuits must be frequently worked on (e.g. television repair), an isolation transformer is used. Unlike ordinary transformers which raise or lower voltage, the coil windings of an isolation transformer are at a 1:1 ratio which keeps the voltage unchanged. The purpose is to isolate the neutral wire so that it has no connection to ground. Thus, if a technician accidentally touched the live chassis and earth at the same time, nothing would happen.
Neither earth fault circuit interrupters (RCD/GFCI) nor isolation transformers can prevent electrocution between the live and neutral wires. This is the same path used by functional electrical appliances, so protection is not possible. However, most accidental electrocutions, especially those not involving electrical work and repair, are via earth -- not the neutral wire.
There were 550 electrocutions in the US in 1993, which translates to 2.1 deaths per million inhabitants. At that time, the incidence of electrocutions was decreasing.  Electrocutions in the workplace make up the majority of these fatalities. From 1980-1992, an average of 411 workers were killed each year by electrocution. 
Electric shock is also used as a medical therapy, under carefully controlled conditions:
Electric shocks have been used as a method of torture, since the received voltage and amperage can be controlled with precision and used to cause pain while avoiding obvious evidence on the victim's body. Such torture usually uses electrodes attached to parts of the victim's body. Another method of electrical torture is stunning with an electroshock gun such as a cattle prod or a taser (provided a sufficiently high voltage and non-lethal current is used in the former case).
The Nazis are known to have used electrical torture during World War II. An extensive fictional depiction of such torture is included in the 1966 book The Secret of Santa Vittoria by Robert Crichton. During the Vietnam War, electric shock torture is said to have been used by both sides. A scene of electrical torture in the American Deep South is included in the 1980 Robert Redford film Brubaker. Amnesty International published an official statement that Russian military forces in Chechnya tortured local women with electric shocks by connecting electric wires to their bra straps . An example in popular modern culture is the electric torture of Riggs in Lethal Weapon.
Advocates for the mentally ill and some psychiatrists such as Thomas Szasz have asserted that electroconvulsive therapy is torture when used without bona fide medical benefit against recalcitrant or non-responsive patients. See above for ECT as medical therapy. These same arguments and oppositions apply to the use of extremely painful shocks as punishment for behavior modification, a practice that is openly used only at the Judge Rotenberg Institute.
Electric shock delivered by an electric chair is sometimes used as a means of capital punishment, although its use has become rare in recent times. Although the chair was at one time considered a more humane and modern execution method than hanging, shooting, or decapitation, it is now being replaced for the same reasons by lethal injection. Modern reportage has revealed that it sometimes takes several shocks to be effective, and that the condemned person may actually catch fire before the process is complete. Source: http://query.nytimes.com/gst/fullpage.html?res=9806E0DA1E3CF930A25757C0A961958260
Throughout the world, execution via electric shock has widely been regarded as inhumane. Other than the United States, only the Philippines used this method for a few years. It remains a legal means of execution in some states of the USA. It is reportedly one of the most grisly forms of modern execution to witness, with smoke or actual flame visible, coming from the prisoner's garments or cap.
Games and pranks
Electric shock is sometimes used as a punishment in novelty games such as Lightning Reaction, Shocking Roulette, Shocking Liar, Laser Shock Guns, and Shocking Tanks. In addition to these games, there are some prank toys such as fake pens, chocolate candy, card holders or cigarette lighter which give out a mild shock.
maltreatment (Physical abuse, Sexual abuse, Psychological abuse)Hypersensitivity (Allergy, Arthus reaction)
|Certain early complications of trauma
|embolism (Air, Fat) - Crush syndrome/Rhabdomyolysis - Compartment syndrome/Volkmann's contracture
|Complications of surgical and medical care
|Serum sickness - Malignant hyperthermia