h a l f b a k e r yCaution!
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This one day, I was at a community pool with no life guard. I was underwater and managed to gently hit one of the pool lights, and I noticed that the cover was very loose and there was water behind the lens. I was quite concerned since I knew the lights were on an automatic timer that came on within
half an hour, and there was no accessable fuse box to turn it off with (it was in a locked shed with no one on-site to open it). This basically meant that if the lights came on and one of them was shorted out, anyone near the light is in big trouble. No one would be able to jump in and rescue them, because they'd get shocked themselves, and there wouldn't be any way to turn off the power. By the time an ambulance got there, it'd most likely be too late because the people in the pool would have been continuously shocked by 110v for 3 minutes. ****** I used to think it would shock everyone in the pool. But now that I know a little more about the matter it seems that only someone within the vicinity of the source would be at any real risk. But you'd still get shocked if you tried to push/pull them away-hence my idea for a switch. *******
If there had been some kind of publicly accessible switch or button that cuts off the pool lights or something, I could have just hit that and gotten back in the pool with no worries. Another situation I can think of where you'd want to be able to shut off the power quickly is if someone had been sucked up against a drain or something like that and unable to get out. With an emergency shutoff switch by the pool, a bystander or lifeguard could stop the pump in seconds without needing access to any pump room or anything like that. The shut off switch should also trip off any outdoor outlets within the vicinity of the pool area if an extension cord of a common length could touch the pool or come near it.
The shutoff switch should be something designed such that it cannot be triggered accidentally (so, not a big red button but something similar to a fire alarm switch, or a button behind a cover) and so that just one activation will shut off all pool filter pumps, pool lights and any outdoor light fixtures or outlets where any metal parts of it can be touched by an average adult or by a child (i.e. a metal light pole, in case it shorted out or got wet). The switch should be resettable without a key or screwdriver, but if it is not reset within 10 seconds, an automatic phone dialing system should contact the pool owner. There should be a buzzer that goes off within this 10 second grace period, so that a parent whose little kid set it off would know, and be able to go over there and push it back up, and also to discourage people from pulling it out of curiosity or as a prank.
I am aware that things like light poles and such are grounded, but occasionally ground connections can come undone or break, leaving no protection in case of an electrical short, but the light on the pole would still work, meaning that it wouldn't be fixed until the repair person came for an actual repair and (hopefully) noticed the broken wire. A shutoff switch would enable any bystander to cut off the power to save someone being zapped by touching a faulty light pole or stuck to a suction drain in the pool.
These should be installed at any community pool or in a hotel pool if no lifeguard or other person with keys to the equipment room is present at all times that the pool is open.
Pool lighting
http://www.poolcent...age_pool_lights.htm
Should include GFCI [csea, Nov 10 2011]
[link]
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I'd have thought that lights in a swimming pool would be on some kind of RCCB, so that they'd shut off automatically if any significant amount of current got diverted into the water. |
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Also, the light fitting itself is presumably grounded, so even if water does penetrate as far as the hot bits, the juice will flow to ground via the light fitting, rather than via the rest of the pool. |
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At any rate I'm not sure this would have been as much of a disaster as you make out. It's current that kills, not voltage; swimmers in a pool connected to a high voltage aren't necessarily in any more danger than a bird sitting on a power line. |
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//managed to gently hit one of the pool lights, and I noticed that the cover was very loose and there was water behind the lens// You mean, you broke it? |
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No, it was loose already. I didn't hit it nearly hard enough to break it. It wasn't cracked or damaged, but there was only one screw left holding it in, and it was loose. I don't know what happened to the other screws (there was definitely more than one screw hole) because I never found them in the pool. If you actually touch the lens, you can feel that it's pretty solid and you'd probably have to strike it with a hard metal object to actually break the lens itself. |
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Also, the pool light leaking may not be as dangerous as I thought originally, but I still think there should be a switch that cuts off the pool pump in case someone gets sucked up against it. |
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Many pool lights run on low voltage (12V) and these days, and any new construction would include a ground fault circuit interrupter (GFCI) [link] which would shut off the power should any (electrical) leakage be detected. |
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I wish someone would make a measure of how much
electricity it takes to electrocute people in water
because this is bound to happened at some point. |
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//how much electricity it takes to electrocute people// |
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I'm no expert on electrocution, but it is generally accepted that it takes ~50 joules (watt-seconds) delivered in a short pulse to stop the heart and kill a person. |
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I'm curious to know how many joules {Volts/Amps/Seconds} are delivered in the paddles to restart a heart? (can't be bothered to look it up just now.) |
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The only figure I can find is 3 volts per centimeter at the heart for defibrillators (which are not used to restart a heart, only to treat certain abnormal heartbeats). That makes sense, as action potentials are triggered by a voltage gradient, rather than by any particular total quantity of energy. |
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Going by that figure, or your 50 joules (assuming that they would have to be delivered within a few seconds), I can state, quite non-rigorously, that a person in a large body of water, more than a metre or so from an exposed 240V or 120V source, is at very little risk. |
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Mythbusters showed that a 120V appliance can be lethal to a person in a bathtub, but not by a huge margin. As the body of water and the distance from the source get larger, the PD experienced by the person would get rapidly smaller. |
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Good point - so my comment should read "little risk of heart attack". |
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//I'm curious to know how many joules {Volts/Amps/Seconds} are delivered in the paddles to restart a heart?// |
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Depends on whether it is monophasic or biphasic. I seem to remember numbers for AEDs running as somewhere around 100 and some joules for the first shock, 300 and some joules for the third shock and something or other for the second. |
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I was once knee deep in Pipe Creek Falls when a bolt of lightning struck near enough that I could feel the juice. I only felt the sensation where the surface/air plane of the water touched my legs. |
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^ that would seem to suggest that the meniscus is a better conductor of electricity |
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This idea is mostly baked. Only difference is that the ones I've seen don't have any auto-dial system. |
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It really should be installed at more pools though. |
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The local pool I used to go to has a red button inside a plastic box with a sign next to it "Emergency pool and electric shutoff". When the box is opened, an alarm sounds. |
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