It is never safe to swim if you hear thunder or see lightning. The definitive answer to whether you should be in the water when a storm is approaching is a non-negotiable “no.” Lightning presents an immediate and serious threat that can travel through water and across the ground surrounding any body of water, making the environment dangerous long before the storm is directly overhead. Protecting yourself requires immediate action and an understanding of how electricity propagates through the environment during a thunderstorm.
Understanding Lightning’s Path Through Water
When a lightning bolt strikes the ground or water, the electrical current disperses radially outward from the point of contact. Water, especially water containing impurities like a pool or lake, is an effective conductor of electricity, allowing the charge to travel across its surface for significant distances. While pure water is a poor conductor, the minerals and chemicals found in pools, lakes, and oceans make them conductive enough to carry a lethal current.
The danger is not limited to those in the water, as the current can travel through the surrounding wet ground, creating a hazard known as step voltage. Step voltage occurs when a person’s feet are positioned at two different points on the ground that carry a significant difference in electrical potential. This potential difference can cause the current to flow up one leg and down the other, potentially leading to cardiac arrest or severe injury.
Lightning does not need to strike the water directly to be a threat. A strike to the nearby ground, a tree, or an adjacent structure can still channel a fatal current into the water and the surrounding area. Furthermore, the electrical surge can utilize vast conductive networks, such as underground pipes and metal fencing, to travel great distances from the initial strike point.
Critical Safety Rules for Exiting the Water
The primary rule for safely managing a thunderstorm near water is to seek shelter immediately upon hearing thunder. This immediate evacuation is governed by the widely accepted 30/30 Rule, which provides a simple guideline for when to suspend activities.
The first “30” relates to the time between seeing a lightning flash and hearing the resulting thunder. If that time is 30 seconds or less, the lightning is close enough to be a direct threat, usually within a ten-mile radius. You should immediately exit the water and move toward a safe, substantial shelter.
The second “30” dictates the waiting period before it is safe to return to the water or resume outdoor activities. Safety protocols require waiting a full 30 minutes after the last clap of thunder is heard or the last flash of lightning is seen. This extended waiting time is necessary because the threat often lingers after the rain has stopped.
Identifying Safe Shelter Locations
Once you have evacuated the water, the goal is to find a safe, fully enclosed location that will shunt a lightning strike away from your body. The safest shelter is a large, substantial building equipped with plumbing and electrical wiring, which provides a path for the electrical current to safely reach the ground. Structures like shopping centers, private homes, and office buildings offer this level of protection.
If a building is not immediately accessible, a hard-topped, enclosed vehicle, such as a car or van, can serve as a suitable alternative. The metal frame of the vehicle provides a protective cage, known as a Faraday cage, that directs the current around the occupants and into the ground. Avoid contact with any metal components inside the vehicle, such as the radio or door handles, and ensure all windows are completely rolled up.
Unsafe locations include small, open-sided structures like picnic shelters, dugouts, porches, or isolated trees, none of which offer adequate protection. Inside any building, you should also avoid contact with plumbing fixtures and electrical appliances. Lightning can travel through the metallic networks of pipes and wires, presenting a continued risk of electrocution even indoors.