For a long time I've been aggravated by being kicked out of pools when there were reports of lightning many dozen miles away. I'm an engineer and spent time as an electronic tech so I'm pretty good on electricity. I went poking around the issue and couldn't come up with a reason why we'd be in more peril in the pool then say, walking out to our cars in the parking lot having been just kicked out of the pool. This was in the '90's so not much info on the web. I tried and tried to reason with lifeguards and pool management, but they were either min. wage lackies or bureaucrats and I got no where.
Around 2005 tho, I went after the issue again. This time info was starting to appear on the web. To include....apparently there has never been a confirmed case of someone getting struck by lighting in an indoor or outdoor pool in the US. Never, at least that was apparently the truth back then. With the bit in my teeth, I contacted one of my physics profs from the mid 80's to get his take on it. I was able to track him down only because he became a sci fi author. He agreed that being in a pool didn't make one especially vulnerable. Armed with those emails and a handful of other printouts, I went to my pool in 2014. They were very cool about it and allowed me to see the text of their insurance on this specific issue. Ultimately they agreed to no longer close the indoor pool unless the storm was "really bad". I couldn't get them to budge on the outdoor pool.
There's a bunch of variables, many very hard to predict, that determine the precise location of a lightning strike. First tho, the cloud's above are charged and therefore attract the opposite charge. That attraction causes invisible "streamers" to go up Earth preferentially up from things that are grounded. A streamer meets a counterpart coming down, and the lightning we see blasts thru that path.
It's invisible, then the strike goes down. I'm pulling this out of distant recall so there's sure to be some errors.
Unlike what we see on TV, water is a crappy conductor. It's the impurities in water that make it a pretty good conductor, salts being a fine way to make water conduct. So pool water is a reasonable insulator. Unlike pool water, you are pretty salty so being immersed in an insulator is not a bad place to be. Grounding the pool doesn't do any good because a) Grounding something attracts lightning. Remember the source of the streamers going up. So grounding the pool would simply attract the water to where you are. 2) The pool water is an insulator. The smart thing to do would be to avoid grounding the pool, use plastic pipes or something, and therefore make the water an even better insulator.
When folks ground a building in order to protect it from lightning, the aren't "preventing" lightning strikes, they are "guiding" the lightning strikes. You put a big piece of steel on top of a building, then connect large electrical conductors over the roof, down the sides of the building, and then into deep stakes into the ground. That gives the lightning energy a nice conductive path on the outside of the building. Sure, it also attracts lighting, but that's unavoidable. So the way to ground a pool is to put a big piece of steel way above it, then connect big conductors from it to the ground, all well away from anywhere people hang out. Of course, this would also attract lightning to the pool.
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