5 March 2021 by Prof Ryan Blumenthal
There is a common misconception that most lightning victims are struck directly by a “bolt” of lightning from the sky. But according to Professor Ryan Blumenthal, a senior specialist forensic pathologist at the University of Pretoria, less than 5% of victims are struck by the lightning flash itself – most lighting-related deaths and injuries occur as a result of other lightning attachment mechanisms.
“A direct lightning strike is probably one of the quickest deaths anyone could have,” Prof Blumenthal says. “The victim is injected with millions of amps and billions of volts. The victim will not see it, hear it or even feel it.”
However, in a recent review article in the Journal of Clinical Pathology, Prof Blumenthal placed focus on how the attachment mechanisms of lightning function to hazardous effect. These mechanisms are behind most deaths or injuries, and include an indirect lightning strike (touch potential), side flash, step voltages (ground potential or Earth Potential Rise – EPR), upward streamers, and blast waves (barotrauma), which surround lightning’s luminous channel.
Lightning can cause a wide range of injuries to both humans and animals. This field of research is known as keraunomedicine or keraunopathology.
Lightning is measured by ground flash density. “This is the amount of lightning that strikes an imaginary piece of ground (one square kilometre) a year,” explains Prof Blumenthal. “Giant’s Castle in the Drakensberg mountain range registers a lightning strike rate of 26 flashes per square kilometre each year. This means that one square kilometre of land in the Giant’s Castle region will be struck, on average, 26 times a year.”
Touch potential accounts for approximately 15 to 25% of casualties. This occurs when lightning travels through a metallic object into a person and they are struck indirectly by touching the metal object. This object could be a corded telephone or a television set that is connected to the grid.
Side flashes are another source of danger, where high voltage passes through a tall object such as a tree or pole, then discharges into a person standing close by. This mechanism accounts for about 20 to 30% of casualties.
“An animal standing near a struck object or close to a flash of lightning to the ground could be injured by step voltages produced by a lightning current flowing through the resistance of the soil (EPR),” explains Dr Blumenthal. “This earth current can then flow along another pathway – up one limb and down another, which could result in injury or even death as, in some animals, the heart is located between the limbs.” EPR is the chief reason large groupings of animals are killed by lightning. It is uncertain what effect this mechanism has on humans.
Another significant cause of death or injury by lightning is upward streamers – which accounts for about 10 to 15% of lightning-related injuries and deaths – where electric fields travel both down from the sky and up from the ground. In such cases, currents can rise up through a person’s body towards the sky, travelling through their heart and brainstem, before the charge collapses back to earth. This could cause arrhythmia and death.
There are also cases where shock waves (barotrauma) emanate from lightning’s luminous channel. Barotrauma can occur when a person is very close to the point of the strike. Thunder can be heard from as far away as 25km; this means there is a significant blast wave surrounding lightning’s luminous channel. This blast wave can tear and tatter a victim’s clothes, rupture eardrums, cause secondary missile formation (shrapnel) as well as conditions such as pneumomediastinum (the abnormal presence of air or gas in the thorax).