Electrical Injury and Death
Electrical Injury and Death
The human body is a good conductor of electricity because it contains a large amount of water and dissolved salts in the form of blood and other body fluids . This means that an electric current may pass easily through the body, a process known as electrocution, causing various types of tissue damage and even death. Most cases of electrocution occur by accident, but still need a thorough forensic investigation. Homicidal electrocution, which used to occur mainly by putting an electrical appliance in a bath with the victim, is now relatively rare.
The amount of damage done by electrocution depends upon the size of the current and the length of time for which it is in contact with the body. According to Ohm's Law, the voltage of the source is equal to the current passing through the circuit—in this case, the body—and the resistance to the flow of current it offers. If the skin is wet, it offers lower resistance than dry skin and so currents passing through the body are higher and so cause more damage. Most cases of electrocution occur from contact with a live wire from the public power supply that has voltages of around 200 volts, depending on the country. Contact with overhead power cables, which carry thousands of volts, can be far more dangerous. The electricity takes the fastest route through the body which is, typically, from one hand to another or from a hand down to the ground.
If the hand comes into contact with a current of around ten milliamperes, then the person feels pain and usually lets go before any real damage can be done. This is known as an electric shock. Larger currents, up to 30 milliamperes, cause the muscles of the arm to go into spasm and then the person cannot let go of the source of the current. This longer contact could cause serious damage to the body. Fifty milliamperes is enough to cause ventricular fibrillation, a condition in which the heart's upper chambers beat irregularly, which generally leads to cardiac arrest, although it can sometimes be reversed by application of a controlled shock from a defibrillating machine.
Contact with high voltage power supplies does not cause cardiac arrest, but will lead to serious internal burns and organ damage. If the head touches an overhead power cable, a current may pass through the breathing control center in the brain stem, leading to respiratory failure and death.
At autopsy , the points of entry and exit of the current may be marked by a burn or a collapsed blister, the latter with a characteristic brown center and pale rim. The hands should always be examined with care, as this is the most common entry point for electrocution. There may, however, be little sign of either external or internal damage, even if the electrocution has been fatal. The pathologist's interpretation may therefore rely much more on the circumstances of the incident rather than on the autopsy findings.
Being struck by lightning is a special case of electrocution. It is always accidental and can give a wide range of findings. Some people do survive a lightning strike, but they are lucky—for they have been exposed to voltages of up to 200 million volts, albeit for just a fraction of a second. A lightning strike causes a range of electrical and thermal injuries to the body, as the victim is exposed not just to high voltage but also an accompanying thermal compression wave like an explosion. Although some people killed by lightning are completely unmarked, an electrocuted corpse may have a bizarre appearance. Sometimes the victim is stripped of clothing by the strike, which may lead investigators to suspect some kind of sexual or homicidal attack. There can be very severe burns, fractures, and lacerations. Metal objects worn on the body, like jewelry or belt buckles, may be completely melted. There is one telling sign of a lightning strike that does not occur in all cases and therefore, cannot be regarded as diagnostic. Lichtenberg figures consist of a red fern-like pattern on the back, shoulders, buttocks, or legs of the victim of a lightning strike. This pattern fades within 12–48 hours without leaving scars or discoloration. The cause of Lichtenberg figures is unclear and they are quite rare. When they are observed, however, it is clear to the pathologist that the person has indeed been struck by lightning.
see also Death, cause of; Death, mechanism of.