Direct vs. Indirect Lightning Strikes

Most people see lightning danger as a bolt of electricity coming from the sky and directly striking a person or object. This type of lightning, called a direct strike, only accounts for 3-5% of all lightning related injuries.

Often overlooked are the dangers of indirect strikes. Two of the most common indirect strike dangers include ground current, or step potential, and side flashes. Ground current/step potential occurs when lightning strikes the ground near a person or object. The current passes from the strike point, through the ground, and into that person or object. A memorable example from 2016 is when more than 300 reindeer in Norway where killed by ground charge from a nearby lightning strike.

When lighting strikes an object directly then jumps the air to strike another object, it is called a side flash. A good example of this would be a tree being struck by lightning with a person standing close it. As the charge travels down the tree, it jumps through the air to strike the person standing. Humid air is often the culprit for this sort of behavior.

Height, shape, and isolation of structures/objects are the dominate factors in determining where lightning will directly strike, though deaths from these strikes are rare. However, direct lightning strikes can have secondary effects that span for miles. It is always better to be safe than sorry; read more on lighting safety do’s and don’ts here. To be safe from both direct and indirect lightning strikes, it is best to do as the National Weather Center advices, “when thunder roars, go indoors.” The safest place during a thunderstorm is always indoors and away from windows.

A direct lightning strike is one in which an object or person is part of the flash channel.

A side flash indirect strike occurs when lightning strikes a taller object and the current jumps from the taller object into a nearby person or object.

Ground current or “step potential” is a type of indirect lightning strike whereby an object or person is struck by the discharge occurring in and along the ground surface from a nearby lightning strike.