Does lightning strike indoor swimming pools? Has anyone ever been hurt or killed? Ann, Oberlin, Ohio
Lightning strikes indoor swimming pools. That's why lifeguards yell, "Everybody out of the pool!" when lightning gets within six to eight miles.
Current from a lightning strike can invade an indoor pool, and hurt people. Here's how: Lightning strikes a power pole outside the pool building. A surge of current races along the electrical wires from the power pole to the pump in the building. The pump moves water and, therefore, contains water; water conducts electricity. The current surge flows from pump wires into pump water, which conducts the electric current into pool water and water splashed around the area.
This endangers people in the pool and walking on the wet floors, because the current then flows through people to ground, along any of various paths: A person standing in the pool, one climbing on the ladder, another touching the underwater lights. The huge current could injure or kill all such people.
When lightning is within five miles of an indoor pool, safe practices dictate leaving the pool, and moving to a dry area of the building — well away from any metal (such as, phone lines, electrical wires or buried pipes). Metal can conduct a bolt's current.
If the "Flash-To-Bang" delay (length of time in seconds between a lightning flash and its subsequent thunder) is 30 seconds, the lightning is five miles away.
Current flowing from a lightning strike is fearsome — averaging about 25,000 amps. For comparison: a reading lamp shines with only one amp of current. In the year 2000, lightning killed two boys in an outdoor pool in Florida.
"The enormous power of a lightning bolt does make the kind of precautions you outlined appropriate, although they may seem extreme to the kid who really wants to go swimming," emails physicist Rod Nave, professor at Georgia State University.
"We could find no reports of deaths or injuries in indoor pools related to lightning causes," says Richard Kithil (opens PDF) of the National Lightning Safety Institute and Kevin Johnston, a senior consultant. They suspect such incidents happen, but go unreported. They have observed: a main circulation pump destroyed, injuries to employees touching electrical panels and the concrete footing of a water slide blown apart.
"There are many reports of injuries/deaths in bathtubs from lightning. This is indirect evidence, of course, but it seems reasonable the same danger exists in (larger) swimming pools," emails Kithil.
Kithil and Johnson conclude: suspend all pool activities (including showers) until 30 minutes after the last observed thunder or lightning.
By the way, over the past 30 years, lightning has killed more people in the U.S. than tornadoes or hurricanes, according to John Jensenius of the National Oceanic and Atmospheric Administration and the National Weather Service.
Further Reading
- Lightning and aquatics safety: a cautionary perspective for indoor pools by Richard Kithil and Kevin Johnston, National Lightning Safety Institute
- Lightning injuries and awareness, University of Illinois
- Lightning current by Rod Nave, HyperPhysics
- Lightning safety, National Weather Service
April Holladay lives in Albuquerque, New Mexico. Her column, WonderQuest, appears every second Monday of the month on globetechnology.com. To read April's past columns, please visit her website. If you have a question for April, visit this information page.
