Running outdoors during a thunderstorm is unequivocally dangerous. Lightning represents an immediate threat to life, as this atmospheric discharge can strike up to 10 miles away from the rain area. If you can hear thunder, you are within striking distance. Lightning is often the first hazard to arrive and the last one to leave the area. The severe weather associated with a storm makes any outdoor activity, especially one that takes you far from shelter, an unnecessary risk.
The Physics of Danger: Understanding Lightning Strikes
A direct strike is relatively rare and is not the only way a person can be injured by lightning. The greatest danger to a person on the ground comes from ground current, also known as step potential. When a lightning bolt hits the ground or an object connected to it, the massive electrical charge dissipates radially outward along the surface. This flow of current generates a voltage gradient across the ground.
The voltage difference created between two points of contact with the ground can be extremely high, even over a short distance of just a few feet. This difference is called step potential, named for the voltage that can develop across a person’s feet during a single step. If a person is standing with their feet apart, the current can enter one leg and exit the other, passing through the lower body. Ground current is responsible for a large percentage of lightning-related injuries and fatalities.
Another risk is a side flash, which occurs when current jumps from a struck object, like a tree, to a nearby person. Standing near a struck object is risky because the current can easily arc across a gap of several feet. Lying flat on the ground is also dangerous because it increases the distance between contact points. This allows a wider path for the ground current to follow through the body.
Why Running Increases Vulnerability
Runners inherently increase their vulnerability during a thunderstorm because they are often in exposed environments far from safe buildings. Routes frequently take people into open fields, along trails, or onto elevated areas like hills or ridges. These environments provide no natural protection and put the person at a higher risk of being the tallest object in the immediate vicinity.
Many runners mistakenly believe that the rubber soles of their running shoes offer protection from a lightning strike. This is a misconception, as the current and voltage in a lightning strike are far too great for the thin layer of rubber to provide insulation. The primary danger is the ground current that travels along the surface, not the direct strike from above. Being highly mobile and distanced from immediate, substantial shelter is the factor that most significantly increases a runner’s risk.
The act of seeking shelter under an isolated tall object, such as a large tree, is particularly hazardous. Trees are often struck, and the current can jump from the tree to anyone standing nearby through a side flash. The activity of running often places the individual in an isolated, exposed position where the risk from ground current is maximized.
Immediate Safety Protocols and Shelter Guidelines
The most important guideline for lightning safety is the “30/30 Rule.” The first part of the rule states that if the time between seeing a lightning flash and hearing the corresponding thunder is 30 seconds or less, the storm is close enough to be dangerous, and you must seek shelter immediately. The second part mandates that you wait a minimum of 30 minutes after the last sound of thunder before resuming any outdoor activity. This waiting period is necessary because lightning can strike even as the storm appears to be moving away.
The safest place during a thunderstorm is inside a large, fully enclosed building that has plumbing and electrical wiring. These structures are designed to conduct the electrical discharge safely into the ground. If a building is unavailable, a hard-topped, fully enclosed vehicle, like a car or van, is the next best option. The metal shell of the vehicle diverts the current around the occupants and into the ground, not the rubber tires.
Unsafe shelters include small sheds, picnic pavilions, covered porches, and, critically, standing under isolated tall trees. If you are caught far from safe shelter and a strike is imminent, you should adopt a last-resort position. This involves crouching low to the ground with your feet together, minimizing contact with the surface. This position helps to reduce the path ground current can take through the body by keeping the feet close together and avoiding lying down. Metal objects, such as watches or backpack frames, should be removed and placed a short distance away.