Being in a swimming pool or near any body of water during a thunderstorm poses a significant danger because water conducts electrical energy. Lightning does not need to strike the water directly to cause harm; the current can travel through the ground or metal components connected to the pool. Understanding the mechanics of this threat is paramount for ensuring personal safety during storm season. Safety protocols provide a clear guide for when to exit the water and where to find refuge, focusing on a specific, measurable distance and time frame.
How Lightning Current Spreads Through Water
Pool water is an efficient conductor of electricity, unlike pure water. The conductivity is enhanced by dissolved minerals, salts, and chemicals, particularly chlorine, which provide mobile ions that allow electrical current to travel quickly.
When lightning strikes the water surface, the enormous electrical charge spreads rapidly across the surface rather than penetrating deeply. This horizontal dispersal creates a hazardous zone that can extend from 20 to 100 meters from the point of impact within seconds.
The danger is not limited to a direct strike on the pool. An indirect strike that hits the ground, a nearby tree, a fence, or a metal structure can still channel current into the pool water through wet concrete, plumbing, or bonding wires. Because the human body is a better conductor than water, a person in the pool becomes the path of least resistance for the electrical current, leading to severe injury or fatality.
The Specific Distance Applying the 30/30 Rule
The question of how close lightning can be before exiting the pool is answered by the “30/30 Rule.” This rule dictates that if the time between seeing the lightning flash and hearing the corresponding thunder is 30 seconds or less, the storm is close enough to be dangerous, and you must seek immediate shelter. This 30-second interval corresponds to a storm approximately six miles away, which is the threshold for immediate evacuation.
To use the “flash-to-bang” method, begin counting immediately after seeing a flash and stop when you hear thunder. Since sound travels about one mile every five seconds, a 30-second count indicates the storm is six miles distant. This is the maximum separation recommended before all outdoor activities should cease.
Lightning is known to strike up to 10 miles away from the center of a thunderstorm, sometimes called a “bolt from the blue.” If you hear thunder at all, lightning is within striking distance. The 30-second count serves as a minimum safety guideline; if thunder occurs before that count, the risk of a strike is unacceptably high, necessitating a quick exit from the water.
Where to Seek Shelter and When to Return
Once the 30-second threshold is met, or the moment you hear thunder, seek safe shelter immediately. A safe structure is a fully enclosed building that features wiring and plumbing, as these systems help ground the structure against a lightning strike.
Unsafe structures offer no protection from electrical current. These include:
- Pergolas
- Gazebos
- Pool houses
- Sheds
- Covered patios
- Open garages
If an enclosed building is unavailable, the next best option is a hard-topped, all-metal vehicle, which acts as a Faraday cage to direct current around the occupants. While inside, avoid contact with plumbing fixtures, electrical equipment, and corded phones, as current can travel through these conductive pathways. Seeking shelter under a tall, isolated tree is highly discouraged, as trees are frequent targets for lightning strikes.
The second “30” in the rule addresses when it is safe to return to the pool. You must wait a minimum of 30 minutes after the last observed flash of lightning or clap of thunder before resuming outdoor activities. This waiting period ensures the entire storm has passed and the lightning threat has moved out of striking range. The danger can persist even after the main rain has stopped or the storm appears to be moving away.