[David Cooper (OP)]

A puzzling tragedy the other day set me wondering about whether it's safe to jump into a pool to try to rescue a struggling swimmer who may be being electrocuted. You wouldn't know where the switch is for anything that might be causing the problem, so is there anything you can do that would make it safe to enter the water? (You also couldn't trust anyone not to turn it back on while you're attempting the rescue.)

There isn't time to dissolve a ton of salt into it and there won't be enough at hand, but maybe there's some kind of liquid that would make the water conductive enough to replicate the properties of sea water through which the current from a lightning strike flows more easily than it does through a person, which is why it's better to stay in the sea than to run up the beach if you're caught in a sudden thunderstorm while swimming. (Fresh water works the other way round: the current flows more easily through you than through the water.)

[syhprum]

The harsh answer IS DONT ATTEMPT A RESCUE ! , every year numerous people die because they attempt to rescue dogs that are apparently drowning (the dogs often survive !) or people who are unconscious due to gas leaking into wells ,cellars etc.
If you think the person unconscious in the pool is there because of a stray electric current contact the pool maintenance or look for a nearby maintenance room where any supply to pool lights can be switched off, faulty pool lighting system is the only likely source off any electric currents in the pool although a safe system is easy to devise.
It is just possible that a fault in a nearby power cable is the cause of the problem so make tests before entering the water even if lights are saftly switched off . 

[alancalverd]

A public pool will have lifebelts with ropes. Whatever the current source in the pool, the flow along a wet rope will be a lot less than through an immersed body. If you are still concerned, stand on the rope or tie it to a deckchair/tree/anti-Semite rather than hold it.

I was testing the x-ray equipment in a private clinic some years back when the owner mentioned that people reported a tingling sensation if they walked from the flowing exercise pool to the jacuzzi. The most significant hazard of medical x-ray equipment is electrocution, so we always test grounding and insulation before anything else, and I had the kit in the car. Turned out that both pools were grounded but to different incoming mains supplies, with anything up to 50 VAC between them.   

Hopefully the lifeguards' training will include knowing where the mains isolation switch is located.

[syhprum]

Three phase supplies and lack of understanding of how to connect them seems to be the cause of the problem ' I used install and service HELL scanners that came with an Y to Y power transform I often found parts of the installation was connected with the parts of the equipment connected between the three output phases of transformer and the centre connection of the incoming supply .
I tried to explain to the instructors how to teach the trainee installers to do it properly but the reaction was how does this native from a primitive third world country think he knows better than we German experts!   

[David Cooper (OP)]

I'd never thought before about there being a need to ground a pool (or indeed that any electrics would be associated with it), but I'm guessing there's an impervious layer that not only stops the water leaking out, but blocks electricity too, so how is the grounding normally done? Round the edge? If, for example, you have a pump with an outlet in the centre of the pool and the electrics go wrong, I can imagine that you could then get a flow of current from the centre of the pool to the edge, and that would pass through anyone who gets too close to the shortest path. If it's only grounded at one side, I could also imagine a current from a faulty light travelling across the pool from one side to the other.

All that aside though, if you see someone struggling in the water and someone who tries to rescue them gets into difficulty too, that would instantly make me think about electricity. You can't dive in to rescue them without the risk of just adding to the death count, and you can't trust the people who wired the thing up to be sure that the current will stop if you flick any particular switch. Throwing a lifebelt on a rope sounds reasonably safe, but the people in the water might not be in a fit state to hold on to it. I'm now wondering if there should be additional safety equipment available at every pool in the form of some kind of wire mesh "clothing" to serve as a Faraday cage.

[syhprum]

There is no evidence that electricity played any part in the drowning of three people in in the Spanish hotel pool

[David Cooper (OP)]

There is no evidence that electricity played any part in the drowning of three people in in the Spanish hotel pool

Indeed, but there's also very little chance of a pump being powerful enough to suck three people down and drown them, and people who can swim don't generally to drown in such quick succession by chance alone. I can only think of one non-magical mechanism by which this might actually have happened, but if anyone has any alternatives to offer, I'm open to any other possible explanations. I did a search for pool electrocutions as soon as I heard about this incident and it uncovered quite a lot of cases which don't appear to have been given the publicity they deserved, leading to the public being in greater danger. I hope that there hasn't been a cover up in this case with something being quietly fixed and the blame being put on the victims, and that possibility needs to be explored. Why would you open a pool again so soon if you haven't found the fault?

[alancalverd]

Hopefully there will be a proper post-mortem. The difference between drowning and electrocution should be reasonably clear. The idea that three fit people can "get into difficulties" in a hotel pool is absurd - the term usually involves breaking waves, temperatures below 10C, or offshore currents in excess of a couple of knots. Humans are almost neutrally buoyant.

[David Cooper (OP)]

I don't know how clear the signs of electrocution would be: it won't necessarily leave burns, and someone in that situation could still show all the normal signs of drowning too, not least because that might still be the main cause of death rather than the heart being stopped by current. It could be sufficient just to have the operation of one's limbs impaired to lead to drowning.

(That said though, it is possible that the information about them being able to swim is incorrect: the pool was deeper than any such unsupervised pool needs to be, so the view of the local police may be right. My interest in this is not restricted to this particular case: some other cases which I read about as a result of it set me thinking about the risk of electrocution in pools in general, and it's something I'd never considered before. Just being aware that there could be such an issue with a pool will make me look at them more carefully in future.)

[alancalverd]

You wouldn't find much water in the lungs of someone who had been electrocuted.

[Bored chemist]

You wouldn't find much water in the lungs of someone who had been electrocuted.

You don't usually find much water in the lungs of someone who drowns.

[alancalverd]

https://radiopaedia.org/articles/drowning-postmortem-findings  Not a lot, admittedly, but with very specific presentations.