What is an electrical shock?
An electrical shock is an injury that occurs when the body comes into contact with a source of electrical energy. The severity of the electrical shock is dependent on several factors such as the :
- the voltage of the electrical source,
- the type of current – direct or alternating current, and
- the type of power source.
Electrical shock injuries in children are more likely to be seen in the home environment while adult injuries are usually in the work environment, particularly in factories and when handling heavy machinery. Apart from the factors relating to the power source, a person’s overall state of health can also determine the outcome of an electrical shock. Effects of the injury can range from electrical burns to death. Prompt medical attention following the incident can prevent a fatal outcome in certain instances.
Electrical Shock Power Source
Severe injury and death is more likely with high voltage and high current. It is possible, however, for fatalities to occur with voltages as low as 110V (household electricity supply) due to the higher current. Similarly low current can be dangerous if the voltage is very high or the resistance low. Voltage alone is not the only factor for the extent of the injury. Current, resistance and duration of exposure are other factors that need to be taken into consideration.
Electrical shock injury can be broadly classified by the power source as :
- Lightning injury – often greater than 10 million volts.
- High-voltage injury – greater than 1,000 volts.
- Low-voltage injury – less than 1,000 volts.
While lightning is extremely high voltage, it only lasts for a fraction of a second and may therefore not always cause fatal injuries.
Alternating current (AC) is significantly more dangerous than direct current (DC). Current plays a major role in determining the extent of injury particularly with low voltage electrical shock.
- 1 to 4 mA (milliamps) = tingling or ‘electricity perception’.
- 3 to 4 mA = pain and loss of muscle control in children.
- 5 mA = disturbing but not painful sensation in adults but a person has enough muscle control to move away from the power source.
- 6 to 7 mA = pain and loss of muscle control in women.
- 8 to 9 mA = pain loss of muscle control in men.
- 16 to 20 mA = intense pain and involuntary muscle contractions.
- 20 to 50 mA = severe muscle contractions and excruciating pain with paralysis of the breathing muscles (respiratory arrest).
- 50 mA to 2,000 mA = ventricular fibrillation, muscle contractions where a person cannot let go, nerve damage and death is likely.
- greater than 2,000 mA = heart muscle stops (cardiac arrest), severe electrical burns and multi-organ damage where is death is very likely.
However, current as with voltage is also influenced by other factors such as resistance and time.
Skin, particularly when dried an callused (thickened), has greater resistance than the internal environment of the body. However, in the presence of wet skin or open wounds the resistance gradually decreases. This can increase the current significantly which can then be very harmful or even fatal. For example, with very dry skin a 120V power source is barely perceived as the current can be as low a 1mA. Wet skin on the other hand has much less resistance and the same 120V power source can deliver current as high as 120mA which can be fatal.
The longer the time period one is contact with the power source the more severe the injury and likelihood of death. Even a difference of a few seconds can make the difference. Long exposure to a lower current has the same effect as short exposure to a higher current. This effect is seen with lightning which only lasts for a few milliseconds and a person can still survive the strike despite the high voltage. The danger, however, is that once involuntary muscle contractions occur then a person may not be able to move themselves away from contact with the power source.
Why is an electric shock dangerous?
There are three ways in which an electric shock can cause injury. Depending on the severity of the injury, it can be fatal.
- Direct tissue damage caused by electricity.
- Burns when the electrical energy is converted to thermal energy (heat).
- Indirect injury with severe muscle contractions and falls.
The more severe injuries are associated with an electrical shock to the chest or head. Here the electrical energy can cause death by :
- Paralyzing the muscles for breathing thereby leading to respiratory arrest.
- Damaging the heart muscle resulting in fatal arrhythmias and cardiac arrest.
- Injuring the brain and nerves that control the breathing muscles.
A person who survives a severe electrical shock may suffer with seizures, paralysis and cardiac problems that can drastically compromise the quality of life and even ultimately reduce the lifespan.
Electrical burns occur with direct contact as the electrical current heats the tissue (electrothermal burns). It is more correctly known as contact burns. Other types of electrical burns may be related to :
- Heat from sparks that form between the power source and another metallic object – electrical arcs.
- Clothes catch alight through electrothermal energy or electrical arcs – flame.
- Heat from the electrical arc burns the skin without the current making contact with the patient – flash burn.
Electric Shock First Aid
Electrical shock injuries need to be treated by medical professionals and depend on the extent of any tissue damage. However, there are a few simple measures that are useful until emergency medical attention can be acquired.
- Turn off the electricity supply.
- Try to separate the patient from the electricity supply. However, neither the energy source nor the victim should be touch with bar hands.
- Cardiopulmonary resuscitation (CPR) should be commenced if there is no pulse or signs of breathing.
- Ideally a person who has sustained an electrical shock injury should not be moved from the spot unless they are at risk of further injury.
- To prevent shock (reduced blood flow through the body), the legs should be elevated while the head should be slightly lowered compared to the trunk.
- Electrical Injuries in Emergency Medicine. Medscape Reference