Lightning is a powerful natural phenomenon. It manifests as a giant spark of electricity, occurring within clouds, between clouds, or between clouds and the ground. This rapid discharge of electricity temporarily equalizes charged regions in the atmosphere. Approximately 2,000 thunderstorms occur globally at any given moment, resulting in about 40 lightning flashes per second worldwide.
Common Forms of Lightning
Lightning manifests in several forms, categorized by where the electrical discharge takes place. Intra-cloud (IC) lightning, the most common type, occurs entirely within a single thunderstorm cloud, jumping between different charged regions. This often appears as a bright illumination of the cloud, earning it the name “sheet lightning” because the actual bolt is hidden from view. Another type is cloud-to-cloud (CC) lightning, which involves electrical discharges between two separate storm clouds. Both intra-cloud and cloud-to-cloud lightning do not pose a direct threat to people or property on the ground.
Cloud-to-ground (CG) lightning involves an electrical discharge that extends from a cloud down to the Earth’s surface. This type of lightning is characterized by its vivid, branching structure as it descends. While less common than intra-cloud lightning, cloud-to-ground flashes are the most hazardous due to their direct interaction with the ground. CG lightning can be further classified as negative (-CG) or positive (+CG), depending on the charge transferred to the ground.
The Most Perilous Lightning Strikes
Among the various types, positive cloud-to-ground (+CG) lightning is considered most hazardous. Unlike the more common negative CG lightning, which transfers a negative charge to the ground, +CG lightning lowers a positive charge from the cloud to the Earth. These flashes originate from the upper parts of a thunderstorm. Positive CG flashes are less frequent, making up less than 5% of all strikes, but they are significantly more powerful.
Positive cloud-to-ground lightning can carry a peak charge and potential that is ten times greater than negative strikes, sometimes reaching as much as 300,000 amperes and one billion volts. They consist of a single, long-lasting stroke, unlike negative lightning which has multiple strokes. A notable characteristic of +CG lightning is its ability to strike many miles away from the main storm, sometimes in areas where the sky appears clear, a phenomenon referred to as a “bolt from the blue”. This unpredictability and immense power contribute to its heightened danger, often causing substantial damage and forest fires.
Mechanisms of Lightning Injury
Lightning can cause injury through several different mechanisms, not just a direct strike. A direct strike occurs when a person becomes part of the main lightning discharge channel. While potentially the most severe, direct strikes account for a relatively small percentage of injuries, around 3-5%. A more common mechanism is a side flash, where lightning strikes a nearby object like a tree or building, and a portion of the current jumps from that object to a person. This accounts for approximately 30% of lightning injuries.
Ground current is the most frequent cause of lightning-related deaths and injuries, responsible for about 40-55% of cases. This occurs when lightning strikes the ground, and the electrical energy spreads outward across the surface. Anyone standing near the strike point can be affected as the current travels through the ground and up through their body. Contact injury happens when a person is touching an object that is struck by lightning, such as plumbing or wiring, allowing the current to pass through them. Upward leaders or streamers are channels of positive charge reaching up from the ground to meet a descending lightning channel. These can cause injury if a person is part of an uncompleted channel.
Protecting Yourself from Lightning
Taking safety precautions during thunderstorms is important. The most widely recognized safety rule is “When thunder roars, go indoors,” meaning that if you can hear thunder, lightning is close enough to strike. Seek shelter immediately in a fully enclosed building with plumbing or electrical wiring, or inside a hard-topped, all-metal vehicle with the windows rolled up. Open structures like carports, gazebos, or dugouts do not provide adequate protection from lightning.
Once indoors, stay away from windows, doors, and porches. Avoid contact with anything that conducts electricity, including corded phones, electrical equipment, and plumbing fixtures like sinks, showers, or faucets, as lightning can travel through these pathways. If caught outdoors with no immediate safe shelter, avoid tall objects like isolated trees, telephone poles, and open fields. Move away from bodies of water, such as ponds, lakes, and swimming pools, as lightning can travel across water surfaces.