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The injury and damage to the human body caused by lightning is due to the transfer of large amounts
of electrical charge flowing from cloud to ground. Some portion of this moving electric current can pass
through, over, or around a victim, causing the injury pattern. This large flow of electrical current damages
the human body through the sudden release of electrical, thermal, and mechanical energy, and the
injuries suffered from a particular lightning strike may involve tissue damage from one or all
of these mechanisms.
Remember, almost three quarters of the people who survive a lightning strike
will suffer life-long severe complications and disabilities.
This damage to the body is caused by the sudden flow of a large electrical current from the lightning strike. This current can range from several thousand amps to several hundred thousand amps, making it potentially lethal. High electrical currents damage living tissue by destroying protein molecules and damaging blood vessels. The extent of the damage depends on the actual path followed by the electrical current as it flows to ground. An electrical current will follow the path of least resistance to ground, and the path followed after a victim is struck depends on a number of details.
The typical resistance of human skin can vary from 1,000 ohms on wet or sweaty skin, up to 1 million ohms on dry, calloused skin. When the skin is dry, there will be a tendency for the electrical current to travel deeper into the body, causing damage to muscle, nerves, and blood vessels. Deeper current travel is also more likely if the victim is grounded (such as by wearing metal sports cleats or touching a metal object). If the victim is wet, there is a greater tendency for the electrical flow to occur over the surface of the body, causing an effect known as "flashover". This produces skin burns, clothing explosion, and other injuries on the outer surface of the body.
A large electrical current flowing through the interior of the body may cause much more dangerous and extensive injuries. The central nervous system is very sensitive to lightning injury, with after-effects ranging from short-term loss of consciousness to long-term impairment of brain function. Seizures, paralysis, amnesia, and coma are all possible results of a lightning strike. The duration of the effects can range from minutes to days to longer, and is dependent on the actual location and types of tissues damage.
Typically, over 40% of lightning strike victims experience heart dysfunction in the form of temporary heart stoppage and longer-lasting arhythmias. The age and pre-injury health of the victim are important in gauging the damage caused by the lightning strike. A person with serious heart problems prior to a lightning strike is much more likely to experience serious and life-threatening heart problems from the strike itself.
A lightning stroke may reach a temperature of 20,000 degrees or more, and this rapid release of heat is the source of thermal injuries. Because a lightning stroke is a short duration event (typically less than a tenth of a second), the thermal energy usually remains at the outer skin level and results in burns and other surface injury.
The lightning strike produces a shock wave in the air as it is suddenly heated and cooled. The strength of the shock wave is dependent on the amount of current in the stroke. Larger strokes produce more energy release and therefore stronger shock waves. These types of blunt trauma injuries are the same as for any form of explosion and can range from broken bones to more severe trauma injuries involving the nervous system.
Lightning-caused injuries fall into four main categories which depend on the actual path the electrical current of the lightning stroke takes as it flows through or over the victim on its way to ground:
Direct strike injury occurs when the victim is hit directly by the lightning bolt, or is in direct contact with a metal object which is hit directly. This type of injury occurs most often in people who are standing in the open (such as on a sports field or under a tree) or who are in contact with a metal object that is struck by the lightning stroke. Direct strike injuries are often the most serious, since the victims are receiving the full strength of the current flow from the strike.
Splash occurs when a lightning strike hits an object (such as a light pole) and then jumps (splashes) to nearby people or objects on its way to ground. This is the most common mechanism for lightning injury, and it is the reason that standing near any tall, grounded object (like a tree, light pole, sports bleachers, etc.) represents a greatly increased chance of injury during a thunderstorm.
Ground current occurs when a lightning strike hits the ground and is then transferred to a victim or victims nearby. Injuries from ground current are usually less severe than those from direct strike or splash incidents, since the strength of the lightning current has been weakened by traveling through the ground However, if the ground is wet or covered with standing water, the amount of weakening might be greatly reduced, increasing the danger of this form of injury. The ground current is also dangerous because it can affect everyone standing close enough to the point of impact, making it a dangerous threat to an unlimited number of people in a storm situation.
These are the injuries caused by the explosive expansion and contraction of the air heated by the lightning stroke. This type of injury is closely related to the victim’s actual distance from the lightning point of impact, and the energy dissipates as an inverse proportion to this distance.
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