Electrocution possible in water even with "low voltage"

[ericsarratt]

In HVAC school I was taught that 24VAC was "safe"; it was low voltage.

And, I have been reading ELECTRIC SHOCK DROWNINGS by Shafer and Rifkin from Mike's we website.

It seems that when you add water into the equation there really isn't a safe voltage. Correct?

Shafer and Rifkin's document reported electrocutions as low as: 4-6 VAC and 17VAC.

 

[Dennis Alwon]

Electrocution usually refers to death. I am not sure how many people die from 4-6 vac but you will get a nasty shock

 

[kwired]

I remember one time on new house the builders (back when many still did many different things that now are contracted to specialists) were cleaning the brick they installed, water and muriatic acid. He asked me about the doorbell wire that was poking through the brick, I said it was energized but is only 16 volts and shouldn't be a problem. Which usually you feel nothing at all if you get across those conductors. He kept working and got a pretty good jolt from it when he was working closer to it. Water alone maybe wouldn't been as bad but I'd guess the acid increased the conductivity.

Electrocution isn't so much about how many volts but rather how much current can find a path through a critical area of the body. At same time higher the voltage is the easier it may be for said current to flow. Calloused hands likely have more resistance than some tender spot elsewhere on the body. Immersion of the body or portions of it in water does increase contact area and water generally is conductive enough because of dissolved minerals and such to carry enough current to be harmful.

 

[HEYDOG]

If you are swimming a much lower voltage could cause enough current to flow to cause your muscles to contract and you wouldn’t be able to swim causing you to drown!

 

[ericsarratt]

Here is a link to the original document on Mike Holt's website:
http://www.mikeholt.com/files/PDF/Electric_Shock_Drownings_Update.pdf

Here are the two incidents which I referenced. There are many, many more, but they are of the higher voltage variety.

Boats are one of my passions so anything related to them (water and electricity) catches my attention.

Until reading this document I had no idea there were so many deaths connected to electricity, marinas and docks. Scary.

34. Mar 18, 2006 Summerset Lake near Desoto, St. Louis, MO. In the early evening a teenage boy
became paralyzed by electric shock, and drowned, while attempting to swim toward a metal ladder attached to a private dock. Two friends were rendered unconscious but were resuscitated and required hospitalization. During several investigations, initially and over the next months, it was determined that the dock wiring was properly installed, the metal dock frame and ladder were bonded, and no loads were operating at the time of the accident. However, clamping the dock supply cable with an AC ammeter disclosed 10 amps flowing (likely in the ground wire) and 4-6 VAC was measured approximately 2 ft. away from the ladder on several separate occasions. The subsequent legal action resulted in a jury finding the local utility at fault. It seems that a near-by underground power distribution cable had a defective (or missing) neutral which caused the neutral current to seek a path back to the substation through the earth and into the lake. This earth leakage current concentrated at the bonded swim ladder resulting in a lethal gradient of more than 2 V/Ft near the ladder. These earth leakage currents are fairly common but this is the first serious incident we have recorded due to this phenomenon.

53. July, 1999 Lake Mohave, AZ. Young man swimming toward stern of a house boat became disabled and drowned, fresh water. Boat had a neutral-ground bond. Home made shore cord “Y” became partly disconnected causing hull to become energized. 17vac measured behind stern-drive.

 

[ericsarratt]

Electrocution isn't so much about how many volts but rather how much current can find a path through a critical area of the body.

Thanks!

 

[Joethemechanic]

Voltage measured across a gradient in the water, isn't the same as source voltage

 

[ActionDave]

If you are swimming a much lower voltage could cause enough current to flow to cause your muscles to contract and you wouldn’t be able to swim causing you to drown!

Exactly.

 

[kwired]

Voltage measured across a gradient in the water, isn't the same as source voltage

Yes but no.

depending on impedance of the path it certainly could sustain a load and voltage at whatever is measured between those points. Most the time it probably won't sustain very much load, but it doesn't take much to be a shock/electrocution hazard.

 

[Joethemechanic]

Yes but no.

depending on impedance of the path it certainly could sustain a load and voltage at whatever is measured between those points. Most the time it probably won't sustain very much load, but it doesn't take much to be a shock/electrocution hazard.

My point is, that dealing with low voltage electrical sources, you are not going to get a lethal gradient across a distance of water. If your source is only 28 volts to begin with, you are not going to electrocute anyone when a wire falls in the water

 

[don_resqcapt19]

My point is, that dealing with low voltage electrical sources, you are not going to get a lethal gradient across a distance of water. If your source is only 28 volts to begin with, you are not going to electrocute anyone when a wire falls in the water

The issue in water is not electrocution, it is electric shock drowning. Only a few volts across your body in the water can disrupt the muscle function to the point that you cannot keep yourself afloat and you drown.

 

[Joethemechanic]

The issue in water is not electrocution, it is electric shock drowning. Only a few volts across your body in the water can disrupt the muscle function to the point that you cannot keep yourself afloat and you drown.

Ok so with a source voltage of 24 , can you give me a real life scenario where you could create a hazardous voltage across a human body in water?

 

[don_resqcapt19]

Ok so with a source voltage of 24 , can you give me a real life scenario where you could create a hazardous voltage across a human body in water?

If you have a 3 volt gradient across your body, that is enough.

 

[Joethemechanic]

If you have a 3 volt gradient across your body, that is enough.

But starting at a maximum voltage of 24, and flowing through some distance of water, how are you going to get to that 3 volt potential across the body?

3 volts is a 2 cell flashlight. Are they dangerous in the water?

 

[don_resqcapt19]

But starting at a maximum voltage of 24, and flowing through some distance of water, how are you going to get to that 3 volt potential across the body?

3 volts is a 2 cell flashlight. Are they dangerous in the water?

If you can get that amount of gradient they could be, but very unlikely you could do that. With the 24 volts it would only be possible if the distance in the water is such that you could have 3-4 volts drop across the length of your body.
Many deaths in water that has electrical equipment have been reported as simple drownings as there is no easy way to determine electric shock drowning without investigating the area where the incident occurred, but the conditions in the after the fact investigation may not be the same as when the incident occurred.

 

[drcampbell]

...It seems that when you add water into the equation there really isn't a safe voltage. Correct? ...

I'm sure there is a safe voltage. After all, your body generates its own voltages, and you're (apparently) not at risk when you're swimming with them, nor do they (apparently) pose a hazard to the other people you're swimming with.

But your body's action potential is in the neighborhood of 0.07 volts. (70 millivolts) For an externally-applied voltage gradient to be safe, it needs to be low enough that it does not interfere with your nervous system's own inherent electrical signals. I would be very skeptical of anything more than a 0.7-volt* (700 millivolts) whole-body exposure.

Action potential - Wikipedia

en.wikipedia.org

* 0.7 volts is a GUESS. NOT a spec, NOT a recommendation, NOT even an expert opinion.

 

[roger]

But starting at a maximum voltage of 24, and flowing through some distance of water, how are you going to get to that 3 volt potential across the body?

Well we don't know the disatnce and salt or fresh. There is no "matter of fact" here

 

[drcampbell]

Well we don't know the distance and salt or fresh. There is no "matter of fact" here

Ocean water is saltier and more conductive than a person. Electric-shock drowning does not appear to occur in ocean water.

 

[don_resqcapt19]

Ocean water is saltier and more conductive than a person. Electric-shock drowning does not appear to occur in ocean water.

The salt water is more conductive than fresh water and less current flows across the person. In fresh water the wet skin is more conductive than the water and more current flows across the person.

 

[ActionDave]

But starting at a maximum voltage of 24, and flowing through some distance of water, how are you going to get to that 3 volt potential across the body?

3 volts is a 2 cell flashlight. Are they dangerous in the water?

You are misreading the or taking the OP too literally. 24V is not the source voltage. Nobody drowns because they fall into the water holding a battery, but it only takes a voltage gradient of around 10V from a faulty wire or stray voltage around a fresh water dock or swimming pool to paralyze someone and they curl up and sink in the water and don't come up.