1000 ways to die - electrified basement water

wayneh

Joined Sep 9, 2010
17,496
...I don't think there are any real chemists here ...
I may not be real, but I am a chemist!

Conductivity of a salt solution depends on several factors. Most important is simply how many ions are in the water, since these are what carry the charges from one pole to the other. One mole of NaCl produces 2 ions, Na+ and Cl-. Magnesium or calcium chloride each give 3; 1 of either Mg+2 or Ca+2 divalent metal ions and 2 Cl- anions. So for a given number of moles dissolved in solution, magnesium chloride will be more conductive than sodium chloride. This also applies to freezing point depression, and explains why (in part) that calcium chloride is preferred over sodium for melting ice. (Lower toxicity to plants is another.)

Another factor is ionic mobility. A chloride anion might be more active than a sulfate anion, for instance. So not exactly equal conductors even if they are at the same molarity.

There are other smaller factors as well. Not worth digging into here.
 

wayneh

Joined Sep 9, 2010
17,496
Distilled is free from all impurities (Theoretically), and also will not conduct.
That's not entirely true. Even pure water has a slight amount of dissociated water in it, H+ and OH-, about 0.1µM each. These are good conductors but are at a very low concentration.
 

tindel

Joined Sep 16, 2012
936
Somewhat on topic -

When I was going to Kansas State we had a half-life experiment in chemistry lab. We all took table salt (if I recall correctly) and radiated it in the school's nuclear reactor took it back to the lab and did some chemistry 101 half-life experiments. Not many people get to do this, so I considered myself pretty fortunate to get some practical radiation experience.

Anyway - to the point... somewhat on topic... The nuclear reactor was cooled using ultra-pure water (extremely pure, continuously purified DI water). The tour guide said that she had put a hair drier in the water once to see if it would fail - it didn't fail until the motor seized. Or that was the story anyway...

I too have been curious if the hair dryer would have acted the same in a bath tub. You have to close the circuit and the current will take the path of least resistance (in the audio band anyway). I'm not convinced that the path of least resistance would be tap water - even with salt in it.
 

wayneh

Joined Sep 9, 2010
17,496
I was disappointed. That video only shows that a GFCI can prevent a bathtub electrocution. Good to know, but I didn't doubt that. The MythBusters episode is pretty good.

So far I think the answer is a definitive "maybe". If someone throws an appliance into your bath - an appliance not protected by a GFCI - you're likely to feel it and under special circumstances you might be hurt or even killed. Definitely something to avoid, but not a guaranteed death sentence.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,782
I was disappointed. That video only shows that a GFCI can prevent a bathtub electrocution. Good to know, but I didn't doubt that. The MythBusters episode is pretty good.

So far I think the answer is a definitive "maybe". If someone throws an appliance into your bath - an appliance not protected by a GFCI - you're likely to feel it and under special circumstances you might be hurt or even killed. Definitely something to avoid, but not a guaranteed death sentence.
Well, that is eye opening. Still a lot of unanswered questions in my head though. Would the same current have passed through the "heart" if there weren't large copper paddles embedded in it? And the main question, WHY? Maybe I'm making a bad assumption that the shortest path through water and least resistance path through water coincide. I still don't "get" why a full amp would travel outside the iron, when they added salt. And if there is a full amp flowing between those plates, then how many other amps are flowing in other parts of the tub? Seems that small space Between the plates represents a very small portion of the available current paths, and if there is a full amp there, then there would be several hundred amps in total flowing through all the bath. Why does the breaker not trip?
 

WBahn

Joined Mar 31, 2012
29,979
I don't remember that episode. I still don't understand why you would get shocked. Why does the current have any incentive to travel outside the toaster enclosure once it's dunked? Why would it decide to travel through the bath water to the grounded drain, when it has a closer, lower resistance path to ground right inside the toaster enclosure, where the copper neutral wire is? I'm not saying that "all the current takes the lowest resistance path to ground" but most of it does. I would think that the current from the live wire in the toaster to the drain would be small, and that the water itself is higher resistance than your body, so the voltage drop across your body should be small.

Do you remember when they did the experiment? I'd like to look it up in netflix.
I don't know the ultimate answer, but throw the following out for consideration:

1) The total current in question is high -- say 10A for argument's sake.

2) The lethal current across the heart is small -- say 50mA for argument's sake.

So MOST of the current can go through the neutral or the water, we only need 0.5% of it to go through the person.

3) The higher the resistivity of the water, the more voltage will be generated as the current passes through it and, thus, the more voltage will appear across the person's body.

4) A person can be electrocuted with a 9V battery if you get through the skin resistance (say with a pair of needles). When wet, much of the skin resistance is lost.

So it would seem to me that if you are in water with very, very high resistivity that you might be safe because there's not enough voltage to push enough current through the water to be lethal even if it all goes through you, and if you are in water with very, very low resistivity that you might be safe because even if all the current is flowing in the water if can't develop enough voltage across you to get a lethal current to go through you. But there is probably a pretty wide range of resistivities (and it would also depend on the amount and distribution of the water about you as well as the location of the electrical entry and exit points) in which you can do both.
 

wayneh

Joined Sep 9, 2010
17,496
WHY? Maybe I'm making a bad assumption that the shortest path through water and least resistance path through water coincide. I still don't "get" why a full amp would travel outside the iron, when they added salt.
Maybe it would help to think of it as field lines. A compass needle can be deflected by a strong magnet over quite a distance. Those magnetic field lines could choose a much shorter return path through the air directly around the poles of the magnet, but they don't. Well, most do, but as WBahn has noted, it only takes a fraction in the wrong place to be a problem.

I've searched around and found evidence that a bathtub event can truly be fatal - most bathtub electrocutions employ a hair dryer and are suicides. But the negative evidence - that it isn't fatal - rarely makes it to the databases. There was a notable case though, where the killer through all the appliances he could find into the tub and, when all that failed, resorted to simply pushing his girlfriend's head underwater to drown her.

So a toaster in the bathtub is an unreliable murder weapon but I'll continue to avoid it. ;)
 

WBahn

Joined Mar 31, 2012
29,979
There was a notable case though, where the killer through all the appliances he could find into the tub and, when all that failed, resorted to simply pushing his girlfriend's head underwater to drown her.
What would have been poetic justice would have been for him to grab the faucet to steady himself, put his hand on her head, push her underwater, get electrocuted himself, and for her to survive.

Of course, I would have settled for a neighbor whacking him in the head with a baseball bat from behind, too.
 

Metalmann

Joined Dec 8, 2012
703
"So a toaster in the bathtub is an unreliable murder weapon but I'll continue to avoid it."





I grew up with the old toasters, they were a lot heavier and would most likely kill a guy, if he had it pounded into his skull enough times.

Enough times, being my point.:D
 

killivolt

Joined Jan 10, 2010
835
I don't know the ultimate answer, but throw the following out for consideration:

1) The total current in question is high -- say 10A for argument's sake.

2) The lethal current across the heart is small -- say 50mA for argument's sake.

So MOST of the current can go through the neutral or the water, we only need 0.5% of it to go through the person.

3) The higher the resistivity of the water, the more voltage will be generated as the current passes through it and, thus, the more voltage will appear across the person's body.

4) A person can be electrocuted with a 9V battery if you get through the skin resistance (say with a pair of needles). When wet, much of the skin resistance is lost.

So it would seem to me that if you are in water with very, very high resistivity that you might be safe because there's not enough voltage to push enough current through the water to be lethal even if it all goes through you, and if you are in water with very, very low resistivity that you might be safe because even if all the current is flowing in the water if can't develop enough voltage across you to get a lethal current to go through you. But there is probably a pretty wide range of resistivities (and it would also depend on the amount and distribution of the water about you as well as the location of the electrical entry and exit points) in which you can do both.
I may die, if my wife want's the insurance money. I like taking a bath and our water is pretty heavy.

Edit: Now that I think about it, I might survive. She won't think about bridging the circuit breaker:)
 
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