Drowning by electrocution

[bthielen]

I'm a little confused. I read the newsletter article from Mike Holt Enterprises this morning about a woman that drowned while swimming in electrically charged water due to an air conditioner malfunction on an ungrounded system of a houseboat. What I don't understand is how does a voltage potential exist across her body, significant enough to kill her, if she is immersed in the current? For example, is it not true that high power line persons work on live power by becoming one with the power line? I've seen Discovery programs where helicopter workers do this.

My first thought was that she was in contact with the boat and the water at the same time which would make sense however the one person that tried to swim toward her claimed he was suffering paralysis while trying to swim toward her, which seems to suggest no contact with the lake bottom.

Anyone have an explanation?

Bob

 

[iwire]

Re: Drowning by electrocution

The water has a high resistance, the potential at one end of your body could be (must have been) different than the potential at the other end.

Remember it is usually skin resistance that keeps us from feeling low voltage but immersed in water that high resistance goes away and very little current is needed to start effecting the body.

I would say it is very lucky that rescuers where not killed.

What about the "No Swimming Electrocution Sign" don't you think repairs to the electrical systems would have been the way to go, not a trip to the sign shop? :roll:

 

[stud696981]

Re: Drowning by electrocution

I saw that sign, what a joke. I'm sure with the picture of that sign any attorney will get a quick out of court settlement!

 

[iwire]

Re: Drowning by electrocution

Originally posted by stud696981:
I saw that sign, what a joke. I'm sure with the picture of that sign any attorney will get a quick out of court settlement!

Yeah that sign screams very loudly

"We are aware of a very dangerous situation and refuse to fix it"

 

[bthielen]

Re: Drowning by electrocution

I agree regarding the sign but what about those signs on mountain highways that warn of falling rock? I mean, chances are if you are in your car moving down the road at x speed and a rock suddenly comes loose overhead, you are not likely to realize it until it hits the road in front of you or the top of your car. Perhaps removing the danger would be more appropriate.

Bob

 

[charlie b]

Re: Drowning by electrocution

In both cases, they are not addressing the danger. They are preparing a defense for a potential future lawsuit. But in the rock slide case, they can't remove the danger. The mountain (or big hill) was put there by someone else, and you can't remove the danger of falling rock without removing the mountain (or big hill). In our local area, there were three people killed last week by a large rock that fell onto their car. It was clearly a tragedy, but I don't know if it was a preventable tragedy.

 

[bthielen]

Re: Drowning by electrocution

Poor analogy I know however if the tax payers are willing to pay the cost, the hillside can be cut back far enough to eliminate the potential danger.

Bob

 

[iwire]

Re: Drowning by electrocution

Originally posted by bthielen:
Poor analogy I know

Bob I did not think so, whenever I pass those signs the thought does come to mind that stopping the rocks from falling would be better.

An act of God as they say is different then human negligence.

 

[charlie b]

Re: Drowning by electrocution

In the recent tragedy that I mentioned above, there were some protective barriers between the hill and the roadway. The problem was that the rock that hit the car was the size of the car it hit.

Here's the news story.

 

[iwire]

Re: Drowning by electrocution

In my luckily limited court experience things like these often come down to words like Prudent and reasonable.

Did the State take reasonable precautions to protect the motorists?

IMO probably yes.


Did this marina take reasonable steps to protect swimmers?

IMO no, not by any stretch of the imagination.

Bob

[ September 15, 2005, 02:47 PM: Message edited by: iwire ]

 

[charlie b]

Re: Drowning by electrocution

Originally posted by bthielen:. . . the one person that tried to swim toward her claimed he was suffering paralysis while trying to swim toward her. . . .

Originally posted by iwire: . . . the potential at one end of your body could be (must have been) different than the potential at the other end.

Lesson learned: If while swimming you feel a shock, your best bet is to tread water, and to do so with minimal kicking and with your hands as close to your sides as you can manage. That reduces the length of your body in the direction of the electrical current flow, and therefore reduces the potential difference between one end your body and the opposite end.

 

[bthielen]

Re: Drowning by electrocution

I must have been misled or misunderstood. I realize that distilled water, being devoid of impurities, is an excellent insulator. I have been taught that non-distilled water, due to other particles and contaminants, is not a very good insulator. This would support my thought that the electrical charge in the water would be generally equal throughout the area. In other words, there would be no measurable potential in say, 5' of distance.

Does lake water actually have that much insulating value to produce a significant difference?

Bob

 

[dillon3c]

Re: Drowning by electrocution

Originally posted by bthielen:
I must have been misled or misunderstood. I realize that distilled water, being devoid of impurities, is an excellent insulator. I have been taught that non-distilled water, due to other particles and contaminants, is not a very good insulator.

Bob

Bob,

They misled me also..I had heard the same..

[ September 15, 2005, 03:47 PM: Message edited by: dillon3c ]

 

[charlie b]

Re: Drowning by electrocution

Yes, salt water will conduct electricity better than fresh water, and perfectly distilled water (which doesn't exit ? nothing is perfect) would conduct less current. But you need to go back to the principle that current takes every available path that leads back to its source. As it moves along any given path, it will encounter some resistance. There will be a voltage drop, however great or however small, between any one point along the path and any other point along the path.

With no person in the water, and with current flowing, look at two points along the current path. Let's say the two points are 5 feet apart. Now consider a 5 foot tall person swimming in that water, with her feet at one of the two points, and her head at the other. Question: How much voltage drop must exist between those two points, for her to receive a painful (even if not fatal) shock?

The resistance of a human body varies widely. It is common to use 300 ohms for discussion purposes. A wet body will have lower resistance. But let's pick a higher value. Let's pick 500 ohms.

A current of 0.025 amps is enough to give a painful shock. Multiply 0.025 amps times 500 ohms, and you get a voltage of 12.5 volts. So that is all you need, within that space of water, to give the swimmer a painful shock.

This process can also lead us to the conclusion that swimming in "electrified fresh water" is more dangerous than swimming in "electrified salt water" I'll leave the reasoning behind this statement to you, as a homework assignment.

 

[iwire]

Re: Drowning by electrocution

Originally posted by bthielen:
This would support my thought that the electrical charge in the water would be generally equal throughout the area. In other words, there would be no measurable potential in say, 5' of distance.

I understand your thought and agree it is surprising that a mere 5' (or less) was this dangerous.

That said it is the only possible answer if these people did not make contact with anything else but the water.

My first though was the victim was touching the boat trying to climb aboard but the rescuers experience disputes that.

 

[charlie b]

Re: Drowning by electrocution

Here is a related article from EC&M magazine from April of last year:

The Case of the Hot Marina.

 

[iwire]

Re: Drowning by electrocution

Thanks for the link Charlie.

Another easily preventable tragedy for all involved.

His handy work killed his daughter and wife.