Being inside a substantial building significantly reduces the risk of a lightning strike compared to swimming outdoors, but the danger is not entirely eliminated. Lightning does not need a direct path to the pool itself to create a hazardous situation for swimmers and staff. Due to the presence of conductive elements within the facility’s infrastructure, most safety organizations recommend evacuating the pool and deck area during active electrical storms.
How Lightning Enters Indoor Structures
Lightning is a powerful electrical discharge that seeks the path of least resistance to the ground. A building’s internal systems can inadvertently provide this route, as a strike does not have to hit the roof directly to pose a threat. Lightning can enter a building through three primary pathways: a direct strike, an indirect strike traveling through utility lines, or a ground current strike radiating through the earth.
Once the electrical charge enters the building, it travels rapidly through conductive materials. These include the extensive network of metal piping used for plumbing, water supply, and drainage, which connects to the pool’s filtration system. Electrical wiring, phone lines, and structural steel supports also act as internal conductors. A lightning strike miles away can induce a surge that travels through these utility systems, energizing areas within the pool facility.
The Role of Water and Electrical Conductivity
The risk to swimmers exists because pool water is a conductor of electricity, despite the common misconception that water alone is a poor conductor. While pure distilled water is an insulator, pool water contains dissolved minerals, salts, and chemicals, such as chlorine compounds, which break down into charged ions.
These charged ions allow the water to effectively conduct an electrical current that has entered the building’s system. When a lightning-induced surge travels through metallic plumbing or electrical components connected to the pool, the entire body of water becomes energized. The current dissipates horizontally through the water, creating a wide danger zone that extends throughout the swimming area.
High-Risk Areas Within the Indoor Pool Environment
The danger within an indoor pool environment extends beyond the water to several specific fixtures and locations. Any area connected directly to the building’s plumbing system presents a significant risk, as metal pipes are prime conduits for lightning-induced surges. Showers and changing facilities, which rely on extensive metal plumbing, should be avoided during a thunderstorm.
Specific metal fixtures immediately surrounding the pool are also hazardous, including ladders, handrails, and diving board supports bonded to the pool structure. The wet concrete deck, which contains steel reinforcement bars, can conduct ground current and should be cleared. Standing near operational equipment, such as filtration pumps and electrical panels, is dangerous due to the potential for a direct electrical surge through the wiring.
Safety Protocols and Recommended Waiting Times
Aquatic facilities adhere to established protocols whenever a thunderstorm is detected. The standard procedure is to immediately clear the pool and deck, moving patrons to a sheltered, non-conductive area away from plumbing and electrical systems. This safe location should be a large, fully enclosed structure away from windows and doors.
The most widely accepted guideline for resuming activities is the “30-minute rule.” This protocol mandates that all aquatic activities remain suspended for 30 minutes following the last observed flash of lightning or sound of thunder. This waiting period is necessary because lightning can strike even after the heaviest part of the storm has passed. Patrons should also avoid contact with all water sources and electrical equipment until the 30-minute period has elapsed.