Kids injured in a pool

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Sahib said:
So for given fault current through pool, which does not change appreciably with change in pool water conductivity, the potential gradient in water depends on its conductivity.
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And the less conductive the pool water is the faster the voltage will change in a short distance.

If you could fill that pool with water that had the same resistance as copper there wouldn't be much potential for electric shock incidents from "stray currents".
 
Sahib, I think that the fundamental problem with your analysis is your assumption that the fault, whatever it might be, can be modeled as a constant current source independent of water conductivity.
In many cases the fault will be a combination of insulation failure and water penetration into a supposedly dry area. The most likely result will be a current which is proportional to the connectivity of the water involved. Over time we can assume that tracks the conductivity of the pool water itself.
Constant current leakage is most commonly associated with capacitive effects or with leakage across failing insulation (such as motor winding varnish) in a dry environment. Or else moisture of relatively constant conductivity such as bathroom steam or domestic or rain water.

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kwired said:
And the less conductive the pool water is the faster the voltage will change in a short distance.

If you could fill that pool with water that had the same resistance as copper there wouldn't be much potential for electric shock incidents from "stray currents".
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Remember it is how much resistance the current path has compared to the path provided by a particular human body is what will determine which one carries more current in any given situation. Water treatment chemicals can change the water resistance enough to matter, but less chemicals means purer water and generally more resistance from the water. Touching a metal object in the water is not the same as being across a voltage gradient that is in water only. That gradient is going to rise or fall rapidly near the metal object if there is a voltage between the water and that object, unless you can get some really superconductive water.
 
The scale of difference in conductivity between fresh and salt water is orders of magnitude greater than the variation of conductivity caused by level of pool chemicals in a fresh water pool.
And a hard short to salt water is more likely to trip a protective device or at least be noticed.
I do agree that salt water swimming issues are far more likely to involve very close proximity to metal than fields in open water.

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A computer simulation program could easily demonstrate effect of pool water conductivity change on potential gradient. But does such a program exist?
 
Fulthrotl said:
i got hit pretty badly with 120 a few years back... tripped a 20 amp lighting circuit
without shorting to ground, arm to arm.

one of the latent problems with electric shock is it will cause a release of
potassium in the blood stream, i was told. someone gets a bad shock,
and a few hours later, has a heart attack 'cause the blood chemistry gets
all screwed up.

dunno about statistics, but if you get shocked badly, go get some blood work
and an ekg and eeg to look for error codes in your control systems.

bad shock... tasting copper afterwards. in my case, it turne the entrance and
exit points deeply discolored, no burning.
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Sorry to hear that and thanks for shaing that unfortunate experience. If I ever take a big hit I'll be sure to visit the ER. I took a hit on Mother's Day painting my house last week. Just touching the wet (plastic) switch on the spray pump motor, but nothing more than a good tingle on one finger.
 
Such programs exist for heat flow. It is a trivial change to reinterpret the equations to current flow. I suspect there are packaged programs, though not necessarily free.

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K8MHZ said:
Sahib's comment has merit.

If you look at data, you will find that almost, if not all, shocks and electrocutions that occur in water occur in fresh water. I have yet to find one that occurred in salt water.
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You're in Michigan where all you have is fresh water.

I've never heard of a freshwater electrocution around here but have heard of many saltwater electrocutions. It's always the dock wiring - lifts, lights, receptacles, etc. Sometimes workers but most commonly kids. Conduit and insulation never hold up in our sun. Bare conductors = very bad. Working in the building dept I started requiring GFCI in the panel before the circuit goes over water - not required by code but I required it anyway. So file a complaint against me for not wanting kids to get killed. Looking back I should have proposed a code amendment. Maybe today someone should.

We've had some other weird electrocutions as happens across the country. Touching a fence in a park and then no forensics can find a voltage on it. Kids playing frisbee in a mall parking lot and touching a light pole. Can't think of others off the top of my head.
 
Fulthrotl said:
i got hit pretty badly with 120 a few years back... tripped a 20 amp lighting circuit
without shorting to ground, arm to arm.
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I find that extremely hard, if not impossible, to believe you tripped a 20 amp circuit with your body.

You may think you did but it had to be something else. The instantaneous trip on a 20 amp breaker is 70 to 100 amps if I remember correctly.
 
mgookin said:
You're in Michigan where all you have is fresh water. I've never heard of a freshwater electrocution around here but have heard of many saltwater electrocutions. It's always the dock wiring - lifts, lights, receptacles, etc. Sometimes workers but most commonly kids. Conduit and insulation never hold up in our sun. Bare conductors = very bad. Working in the building dept I started requiring GFCI in the panel before the circuit goes over water - not required by code but I required it anyway. So file a complaint against me for not wanting kids to get killed. Looking back I should have proposed a code amendment. Maybe today someone should. We've had some other weird electrocutions as happens across the country. Touching a fence in a park and then no forensics can find a voltage on it. Kids playing frisbee in a mall parking lot and touching a light pole. Can't think of others off the top of my head.
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I can only go by what is written, which does not agree with your statement. The part about saltwater, not the part about me being in Michigan. :p

"ESD remains a freshwater phenomenon. Fresh water is highly resistant to electrical flow, so a person swimming in fresh water becomes the path of least resistance. Seawater?s salt content makes it more than 500 times more conductive than fresh water. This, along with a person?s natural skin/fat resistance, causes almost all the electricity to flow around a swimmer in seawater. Fresh water focuses almost all the electrical flow through the person ? and it doesn?t take much electrical flow to kill."
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http://www.boatingmag.com/how-to/electric-shock-drowning-prevention

"During a recent PE class, I saw a Mike Holt DVD where he and the panel discussed the Electrocution Potential of fresh Water versus Salt Water. Mike stated that Fresh Water had more potential and and could create a deadlier situation than a likewise scenario with Saltwater."
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http://forums.mikeholt.com/showthread.php?t=77828
 
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If a person is directly touching energized metal, the lack of high potential over distance will not save him.
Similarly if a high current (amps) is flowing through the salt water, even 1/1000 if that amount (milliamps) flowing through the swimmer can still be fatal.

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iwire said:
I find that extremely hard, if not impossible, to believe you tripped a 20 amp circuit with your body.

You may think you did but it had to be something else. The instantaneous trip on a 20 amp breaker is 70 to 100 amps if I remember correctly.
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Even if it was only 20 amps, that would mean a body resistance of 6 ohms. I don't think that is likely. Body resistance from hand to hand is more like 600 - 1200 ohms. There are hot dog cookers that use 120 VAC stuck in the ends of the hot dogs to cook them and they don't come close to blowing even a 15 amp breaker.
 
K8MHZ said:
Even if it was only 20 amps, that would mean a body resistance of 6 ohms. I don't think that is likely. Body resistance from hand to hand is more like 600 - 1200 ohms. There are hot dog cookers that use 120 VAC stuck in the ends of the hot dogs to cook them and they don't come close to blowing even a 15 amp breaker.
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Funny I was thinking of my trade school hot dog cooking experiments. :)

On a more serious vain I was thinking that we are about 60% water and two 120 volt leads placed in water 18" apart will not come close to tripping a 20 amp breaker in either the instantaneous or long time modes.
 
iwire said:
Funny I was thinking of my trade school hot dog cooking experiments. :)

On a more serious vain I was thinking that we are about 60% water and two 120 volt leads placed in water 18" apart will not come close to tripping a 20 amp breaker in either the instantaneous or long time modes.
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It's not the water in our body that conducts electricity, it's the stuff dissolved in it that does. Hot dogs must have a lot of it.
 
I just remembered, those things were called 'Hot Doggers'

th
 
K8MHZ said:
It's not the water in our body that conducts electricity, it's the stuff dissolved in it that does.
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I understand that, however if you take the water away I bet beyond being very dead we would be very poor conductors.

Everyone loves to point out pure water is non conductive but pure water is pretty rare.
 
K8MHZ said:
It's not the water in our body that conducts electricity, it's the stuff dissolved in it that does. Hot dogs must have a lot of it.
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:thumbsup:
Lots of salt, including sodium nitrates and nitrites to harm your body when you ingest them.

Actually, if you want to be picky, it is the water with the stuff dissolved in it, not either the water or the stuff by themselves.
 
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