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Old 13th November 2012, 08:53 PM   #1
tyrfenrirbane
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Electrical resistance of the Human Body

Okay somebody with a better science background than me. I don't believe in the mystical but things look mystical when you don't understand the science behind them. when i was a stupid kid. i would meditate when when holding one prong of a voltimeter in either hand. when i had it set to measure resistance, it would drop significantly when i would meditate. if it helps i was breathing very deeply. Can somebody explain the science behind this so i can stop thinking about it? It's really bothering me. could it be as simple as my hands getting sweaty?
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Old 13th November 2012, 09:43 PM   #2
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Originally Posted by tyrfenrirbane View Post
Okay somebody with a better science background than me. I don't believe in the mystical but things look mystical when you don't understand the science behind them. when i was a stupid kid. i would meditate when when holding one prong of a voltimeter in either hand. when i had it set to measure resistance, it would drop significantly when i would meditate. if it helps i was breathing very deeply. Can somebody explain the science behind this so i can stop thinking about it? It's really bothering me. could it be as simple as my hands getting sweaty?
Sure it could, the resistance or conductivity (inverse of resistance) of skin is variable. Generally, if I recall correctly, in the mega-ohm range. One of those factors is moisture. When your skin is wet its resistance is reduced to perhaps one 10th the dry value (again if I remember correctly). So as holding on to something occludes evaporation (under even normal temperatures) moister tends to build up reducing resistance.


Oh, also if you're focusing on the reading of a meter and its implications, you may not be meditating properly.

Try some comparative tests, meditating or say watching TV. Skin conductivity is one of the factors measured in lie detectors. The precept being that under stress you sweat more.


http://en.wikipedia.org/wiki/Skin_conductance

ETA:

And welcome to the forum tyrfenrirbane.
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Last edited by The Man; 13th November 2012 at 09:45 PM. Reason: ETA and typo
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Old 13th November 2012, 11:04 PM   #3
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That was helpful, thank you. Though i actually did have a friend watch the reading for me, but we were having light conversation, but if it really was just skin moisture, it doesn't make two licks anyway.

Thanks for the welcome. I'll know where to go if I have questions like this from now on. Facebook is not helpful.

Last edited by tyrfenrirbane; 13th November 2012 at 11:05 PM. Reason: Being polite.
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Old 13th November 2012, 11:30 PM   #4
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Originally Posted by tyrfenrirbane View Post
Okay somebody with a better science background than me. I don't believe in the mystical but things look mystical when you don't understand the science behind them. when i was a stupid kid. i would meditate when when holding one prong of a voltimeter in either hand. when i had it set to measure resistance, it would drop significantly when i would meditate. if it helps i was breathing very deeply. Can somebody explain the science behind this so i can stop thinking about it? It's really bothering me. could it be as simple as my hands getting sweaty?
It is as simple as you say. Note, as well, that the amount of pressure exerted on the electrode will also produce an effect.

However, if you were meditating and the meditation practice had, as would normally be expected, a relaxing effect, I would expect resistance to go up (or, another way of saying it, I would expect conductance to go down) rather than resistance going down (or, another way of saying it, rather than conductance going up). A relaxation response implies a lowering of your sympathetic drive which should result, all other things being equal*, in decreased perspiration. You might possibly be misremembering the effect (either that or staring at the meter actually resulted in increased arousal).

Both an ideomotor effect and a biofeedback effect could also account for this sort of effect. That is, given a certain expectation, you could probably involuntarily train yourself to produce the correct response to match the expectation. This would happen by either by unconsciously altering the grip on the electrode (ideomotor) or by controlling your autonomic responses (biofeedback --this is probably unlikely as it should be much more difficult to do but it is definitely not impossible).

So it is, indeed, not particularly mystical and the effect could be produced a few ways.

*I mean, this obviously won't apply if you step into a sauna.
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Old 13th November 2012, 11:47 PM   #5
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In a classroom you would have been chided severly. The 9v cell in the volt meter or multi-meter could cause the few mili-amps needed to disrupt your heart. Unlikely? Yes. But that would have stopped the tutor barking angrily at you to stop mucking about.


By the way, you just described how toy lie detectors work.
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Old 14th November 2012, 01:34 AM   #6
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Originally Posted by Tomtomkent View Post
In a classroom you would have been chided severly. The 9v cell in the volt meter or multi-meter could cause the few mili-amps needed to disrupt your heart. Unlikely? Yes. But that would have stopped the tutor barking angrily at you to stop mucking about.


By the way, you just described how toy lie detectors work.
Only if the shunt resistor failed to a short (very "Unlikely"). Heck in my electronics class one guy would grab the the probes of a 300 V (dc) power supply just to wake himself up before class. Don't know what eventually became of him (hopefully not an electronics teacher).
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Old 14th November 2012, 01:49 AM   #7
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Originally Posted by tyrfenrirbane View Post
That was helpful, thank you. Though i actually did have a friend watch the reading for me, but we were having light conversation, but if it really was just skin moisture, it doesn't make two licks anyway.

Thanks for the welcome. I'll know where to go if I have questions like this from now on. Facebook is not helpful.

No problem, ask whatever you want and I'm sure there are people here that can and will help.
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Old 14th November 2012, 02:18 AM   #8
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Originally Posted by Tomtomkent View Post
In a classroom you would have been chided severly. The 9v cell in the volt meter or multi-meter could cause the few mili-amps needed to disrupt your heart. Unlikely? Yes. But that would have stopped the tutor barking angrily at you to stop mucking about.


By the way, you just described how toy lie detectors work.
A nine Volt battery can't force enough current through your body to affect your heart through your skin.
HOWEVER:
If the points of the probes are sharp enough to puncture the skin and poke into a blood vessel and you manage to hit a blood vessel with both probes, then you could have a problem. Do NOT put your fingers on the points of the probe and press down hard.

As for skin resistance, I must be a weirdo. Everybody blathers on about readings in the megaohm range, but I find that my resistance from thumb to thumb to only be in the 20 to 30 thousand ohm range.

Last edited by MortFurd; 14th November 2012 at 02:43 AM.
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Old 14th November 2012, 02:53 AM   #9
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Originally Posted by MortFurd View Post
A nine Volt battery can't force enough current through your body to affect your heart through your skin.
HOWERVER:
If the points of the probes are sharp enough to puncture the skin and poke into a blood vessel and you manage to hit a blood vessel with both probes, then you could have a problem. Do NOT put your fingers on the points of the probe and press down hard.

As for skin resistance, I must be a weirdo. Everybody blathers on about readings in the megaohm range, but I find that my resistance from thumb to thumb to only be in the 20 to 30 thousand ohm range.
Hmm, put you in a liquid nitrogen bath and you might just become the first superconductive human (in human conductivity terms that is)!!! Can we get Stan Lee in on this?

Though seriously, since my days in an electrical laboratory I've always tacitly wondered what the expanse of human skin conductivity is under controlled conditions. I surmise some studies have been done but have never bothered to actually find out. Well, at least back then there wasn't the ease of availability of such studies as there probably is now.



ETA:
In that laboratory we designed and tested connectors and hot line tools used in power distribution and transmission. Transmission being the high tension lines you might see along a highway (over 100 kV) and distribution being those along (or under) your street (30 to 50 kV).

The following is an example of human interaction with what is just about the distribution range (25 kV) . Skin resistance don't matter much in such cases, you don't have to actually touch it, just get close enough.

Not suitable for the squeamish!!!

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
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Last edited by The Man; 14th November 2012 at 03:59 AM. Reason: ETA: and bold
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Old 14th November 2012, 09:22 AM   #10
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Originally Posted by MortFurd View Post
A nine Volt battery can't force enough current through your body to affect your heart through your skin.
HOWEVER:
If the points of the probes are sharp enough to puncture the skin and poke into a blood vessel and you manage to hit a blood vessel with both probes, then you could have a problem. Do NOT put your fingers on the points of the probe and press down hard.
With 9v, even if the probes were applied directly to the heart there shouldn't be a problem.
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Old 14th November 2012, 09:27 AM   #11
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Originally Posted by Modified View Post
With 9v, even if the probes were applied directly to the heart there shouldn't be a problem.
Isn't the (milli) wattage going thru the heart more important anyway that any value of volt without ampere and ampere without volt ?
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Old 14th November 2012, 11:22 AM   #12
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Not true. Cardiac pacemakers apply a stimulus of around 1V (variable depending on measured sensitivities)
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Old 14th November 2012, 11:53 AM   #13
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Buggerations. It the multimeter with a insulation resistance test and considerably more powerful battery I was thinking of. My bad.… far too easy to turn the dial to the wrong setting.


Admittedly the voltages I work on tend to be a wee bit higher for the last ten years or so...
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Old 15th November 2012, 06:30 AM   #14
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Originally Posted by Aepervius View Post
Isn't the (milli) wattage going thru the heart more important anyway that any value of volt without ampere and ampere without volt ?
Yes but power (wattage) is dependent on those other variables. Your two independent variables are applied voltage and resistance (or impedance in a AC consideration).

In most test applications the applied voltage (across the test object) is going to be significantly less than the power source (like a battery) voltage. Generally it is as minimal as possible to get a reliable reading which is generally the voltage across some internal know resistor inside the device. Point being most of the voltage is dropped internally (to get the reading) and minimal applied to the test object to prevent potential damage or heating (changing the test object resistance from current ambient temperate value).


http://en.wikipedia.org/wiki/Bridge_circuit
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Old 16th November 2012, 10:07 PM   #15
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Originally Posted by ChumpusRex View Post
Not true. Cardiac pacemakers apply a stimulus of around 1V (variable depending on measured sensitivities)
I'm not sure. I know it takes about 6 times more DC current than AC current to cause heart fibrillation. 9v DC might only cause a skipped or extra beat when applied and when removed.
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Old 18th November 2012, 05:46 AM   #16
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Measuring electrical signals from the human body is notoriously difficult and just grabbing an steel electrode in your hand is not the most reliable way. That said there are a few known things that affect measured responses:
Skin stretch- changes in the thickness of skin will change it's impedance and there are surprising large changes in skin thickness due to stretch when you move, even a little.
Motion artifacts- I know more about these when it pertains to liquid-junction electrodes, but in short ions tend to build around the unstirred layer of an electrode and when even tiny motions take place this layer is disrupted, creating an artifact.
Perspiration- if you're using bare metal against skin perspiration is going to make a big difference. When you sweat water leaves your body due to the osmotic gradient created by salt moving ion channels, so sweat has a lot of Na/K Cl. Having a salt-metal junction changes the redox potential of the electrode- essentially creating a small battery which will offset any measurement.Small changes in perspiration also have large changes to the conductivity of skin as it provides a "salt bridge" for some of the current.
Noise--
Electrical measurement of skin would be very prone to 60hz "buzz" from the environment. This results from your equipment being improperly grounded, and/or inductance from the electrical wiring the goes through every building which (in the US) oscillates at 60 hz.
Those are just a few possible sources of error. When scientists/health people measure, say, eeg signals they control for some of these effects by using a high quality amplifier/chart recorder and high quality electrodes, (normally a floating Ag/AgCl electrode which makes contact through a conductive "jelly")

Without controlling for more possible sources of error your experiment really does not tell us anything.
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Old 18th November 2012, 07:12 AM   #17
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On my digital meter, I can lick my fingers, grab a probe in each hand, and get about 180 ohms, give or take. That used to cause "interesting" problems when I was developing resistive films with a resistance of 355 ohms per square. One of our newly-minted, wet-behind-the-ears engineers kept telling me the films were too conductive. I had him show me, and sure enough, his readings were low. UNTIL I had him hold on to the surface probe by the insulating block -- NOT the metal probes -- and the magical value of 355 ohms reappeared.

(There's nothing more dangerous than a brand-new engineer after two weeks on a new job: he knows how to turn everything on.)

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Old 18th November 2012, 12:49 PM   #18
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Originally Posted by Modified View Post
I'm not sure. I know it takes about 6 times more DC current than AC current to cause heart fibrillation. 9v DC might only cause a skipped or extra beat when applied and when removed.
The issue is the timing of the stimulus; and, to an extent, that the rate of change of current is also a contributor to the stimulus, not just the current.

If a stimulus is applied while the cardiac muscle is electrically recovering from a beat, there is a risk of triggering catastrophic electrical disturbance: ventricular fibrillation. Cardiac pacemakers contain sophisticated sensing circuits which detect beats and inhibit another stimulus until after electrical recovery to avoid causing sudden death.
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Old 19th November 2012, 02:33 AM   #19
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Originally Posted by Beanbag View Post
On my digital meter, I can lick my fingers, grab a probe in each hand, and get about 180 ohms, give or take. That used to cause "interesting" problems when I was developing resistive films with a resistance of 355 ohms per square. One of our newly-minted, wet-behind-the-ears engineers kept telling me the films were too conductive. I had him show me, and sure enough, his readings were low. UNTIL I had him hold on to the surface probe by the insulating block -- NOT the metal probes -- and the magical value of 355 ohms reappeared.

(There's nothing more dangerous than a brand-new engineer after two weeks on a new job: he knows how to turn everything on.)

Beanbag
Are you sure about that? My dry resistance is about 2 Meg ohms, and wet is about 200K ohm. Maybe you mean 180K? Because at 180ohm you could
hurt yourself with a 9 volt battery. (9v/180ohm = 50mA)
What is strange is that while you die at around 100 - 200 mA,(depending on DC or AC and frequency) higher currents are often survivable, as long as you get immediate resuscitation.

-LF
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Old 19th November 2012, 10:29 AM   #20
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Originally Posted by tyrfenrirbane View Post
That was helpful, thank you. Though i actually did have a friend watch the reading for me, but we were having light conversation, but if it really was just skin moisture, it doesn't make two licks anyway.

Thanks for the welcome. I'll know where to go if I have questions like this from now on. Facebook is not helpful.

This is a very good rule to remember.^^^^^
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Old 19th November 2012, 10:43 AM   #21
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Originally Posted by LongFuzzy View Post
Are you sure about that? My dry resistance is about 2 Meg ohms, and wet is about 200K ohm. Maybe you mean 180K? Because at 180ohm you could
hurt yourself with a 9 volt battery. (9v/180ohm = 50mA)
What is strange is that while you die at around 100 - 200 mA,(depending on DC or AC and frequency) higher currents are often survivable, as long as you get immediate resuscitation.

-LF
I'm not sure if I can hurt myself with 9V battery .. but with wet fingers 9V battery gives me significant shock and it's almost impossible to hold circuit 'closed'.

Skin moisture would not change very rapidly, but blood circulation can change in seconds. For meditation I would expect blood circulation in hands to improve. Some simple biofeedback sensors only measure amount of blood in fingers or ears .. and they are good enough to control object on the screen with your 'thought' .. the feedback is very fast, just a few heartbeats. These sensors do not use conductivity though, but IR light transparency. Still I think it would have major effect on conductivity.

Some people also have rather thick skin, especially people who work hard using their hands .. this again can drastically reduce conductivity.
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Old 19th November 2012, 11:04 AM   #22
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Originally Posted by Modified View Post
With 9v, even if the probes were applied directly to the heart there shouldn't be a problem.
I used to test 9V batteries by licking them. A good battery will give your tongue a nice little jolt. A weak one you can barely feel. It's probably not as good as an actual battery tester, but as a quick and dirty means of ruling in or out the battery as the reason a device isn't working, it's somewhat useful.

LOL at tne idea that a 9V battery has any risk of killing or injuring you.
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Old 19th November 2012, 02:49 PM   #23
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Originally Posted by CORed View Post
LOL at tne idea that a 9V battery has any risk of killing or injuring you.
http://www.darwinawards.com/darwin/darwin1999-50.html

I guess it wasn't just the Insulation Resistance Tester that my tutor could have been worried about.
You live and learn (in most cases).
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Old 20th November 2012, 02:01 PM   #24
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Originally Posted by Tomtomkent View Post
http://www.darwinawards.com/darwin/darwin1999-50.html

I guess it wasn't just the Insulation Resistance Tester that my tutor could have been worried about.
You live and learn (in most cases).
Volts don't kill.
Ohms don't kill.
Amps KILL!!!!
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Old 20th November 2012, 02:15 PM   #25
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Originally Posted by fuelair View Post
Volts don't kill.
Ohms don't kill.
Amps KILL!!!!
About 0.2 of them... (And I'm not entirely sure why you think that point was in contention at all in my post).
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Old 20th November 2012, 04:40 PM   #26
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Originally Posted by CORed View Post
I used to test 9V batteries by licking them. A good battery will give your tongue a nice little jolt. A weak one you can barely feel. It's probably not as good as an actual battery tester, but as a quick and dirty means of ruling in or out the battery as the reason a device isn't working, it's somewhat useful.

LOL at tne idea that a 9V battery has any risk of killing or injuring you.
Sure, but when you lick the battery the circuit path is from one terminal to the other just across your tongue. Were you to have tested batteries by touching them to your exposed heart, the effect may have been more serious.
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Old 20th November 2012, 04:54 PM   #27
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Originally Posted by fuelair View Post
Volts don't kill.
Ohms don't kill.
Amps KILL!!!!


http://youtu.be/wH4x412oz2k?t=1m50s



No volts, no amps

More resistance (Ohms) with the same volts means less amps (even when pushing trains).
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Old 20th November 2012, 05:04 PM   #28
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Totally layperson explanation after learning how touch switches work: we are all capacitors. We have space (capacity) for a current to flow into.

By all means anyone correct me if I'm wrong.

So let's see, "it would drop significantly when i would meditate. if it helps i was breathing very deeply."

Hmm, lots of possible variables, they've been mentioned. I'd like to try it myself to see what I think.
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Old 20th November 2012, 10:35 PM   #29
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Originally Posted by Tomtomkent View Post
http://www.darwinawards.com/darwin/darwin1999-50.html

I guess it wasn't just the Insulation Resistance Tester that my tutor could have been worried about.
You live and learn (in most cases).
I don't believe the story.

The idea that a current of between 10 and 100 mas is enough to kill a human requires that the source be AC. It turns out that a frequency of between 40 and 400 Hertz can kill humans by disrupting the heart. If a DC current is applied serious damage to the heart is required.

This issue goes back to the days of Edison who was pushing his DC system and decried the AC systems because of the potential to kill people. He was right about that but wrong about the possibility of implementing his impractical DC system ideas, so AC won out. There were ghoulish electrocution experiments done on convicts at the behest of Edison associated with all that.

My first guess is a the sailor repeated a story that was made up by the instructor to reinforce his point that electricity can be dangerous. My second guess is that maybe something vaguely like this happened but the story has become so distorted that it isn't possible to sort out what was true here.

Originally Posted by Skeptic Ginger View Post
Totally layperson explanation after learning how touch switches work: we are all capacitors. We have space (capacity) for a current to flow into.

By all means anyone correct me if I'm wrong.

So let's see, "it would drop significantly when i would meditate. if it helps i was breathing very deeply."

Hmm, lots of possible variables, they've been mentioned. I'd like to try it myself to see what I think.
The human body can be modeled as a capacitor but the capacitance is extremely small. The capacitance model for the human body is used for building electrostatic generators that duplicate the effect of an electrostatic discharge from a human body. The size of the capacitor is usually around 150 picofarads I think and the ESD simulator can typically be charged up to voltages as high as 30,000 volts. The discharge from a human body model ESD generator set to 30,000 volts is enough to create a nasty little burn mark in a person and it will usually produce language that would be filtered by the automatic censor here at JREF in the person getting shocked. He will however be absolutely alive after the event unless he was dead before hand.
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Old 20th November 2012, 10:57 PM   #30
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Originally Posted by Tomtomkent View Post
About 0.2 of them... (And I'm not entirely sure why you think that point was in contention at all in my post).
I did not in any way think that, it was quite clear - just put it in very short form...a summary of electrics and which is the stranger-danger one!!
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Old 21st November 2012, 01:36 AM   #31
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Originally Posted by davefoc View Post
I don't believe the story.
Your belief or lack thereof is not relevant.

Originally Posted by davefoc View Post
The idea that a current of between 10 and 100 mas is enough to kill a human requires that the source be AC. It turns out that a frequency of between 40 and 400 Hertz can kill humans by disrupting the heart. If a DC current is applied serious damage to the heart is required.
As ChumpusRex noted before...

Originally Posted by ChumpusRex View Post
The issue is the timing of the stimulus; and, to an extent, that the rate of change of current is also a contributor to the stimulus, not just the current.
DC or AC, hit the heart at the right time with a change in electrical potential and you've got a change in well, life potential. One way or the other. While AC potentials are specifically changing over time. With DC changes are more limited (almost excluded)

Originally Posted by davefoc View Post

This issue goes back to the days of Edison who was pushing his DC system and decried the AC systems because of the potential to kill people. He was right about that but wrong about the possibility of implementing his impractical DC system ideas, so AC won out. There were ghoulish electrocution experiments done on convicts at the behest of Edison associated with all that.
Indeed there were, however it don't matter. One way or both enough current across the heart to sufficiently disrupt it's function and you're done (heart ways that is)

Originally Posted by davefoc View Post

My first guess is a the sailor repeated a story that was made up by the instructor to reinforce his point that electricity can be dangerous. My second guess is that maybe something vaguely like this happened but the story has become so distorted that it isn't possible to sort out what was true here.
A salt solution, like blood, is a good conductor. It's like having wires plugged directly into ones heart.

Originally Posted by davefoc View Post

The human body can be modeled as a capacitor but the capacitance is extremely small. The capacitance model for the human body is used for building electrostatic generators that duplicate the effect of an electrostatic discharge from a human body. The size of the capacitor is usually around 150 picofarads I think and the ESD simulator can typically be charged up to voltages as high as 30,000 volts. The discharge from a human body model ESD generator set to 30,000 volts is enough to create a nasty little burn mark in a person and it will usually produce language that would be filtered by the automatic censor here at JREF in the person getting shocked. He will however be absolutely alive after the event unless he was dead before hand.

The human body can be modeled like many things. "as a capacitor" just means that it can hold a charge (to some degree or other). Electrostatic discharges are a result of such. It's electro-dynamics, how and where those and other charges flow (and if through ones heart or related tissues). Statics become dynamics when in transition but it is the transition period that it becomes relevant. Sure a "30,000 volt" static potential might seem like a lot but when dissipated in a fraction of a second, like when you touch a door knob after rubbing your socked feet on a carpet, it is simply a momentary, well, shock.


As I said before, hot line tools (for distribution and transmission) were one of the things we were designing and testing. If you can get to the same potential as a hot line it can't shock or kill you. Though there can be other problems....(particularly in helicopter assisted or other transmission hot line work). In the video below you can see the static charge as the deposited workers reach the potential of the line and then the discharge of the helicopter as it leaves in this case.

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.
I AGREE
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Old 21st November 2012, 03:22 AM   #32
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Originally Posted by The Man View Post
Your belief or lack thereof is not relevant.



...
OK, that is your right to decide that. Your post seems to suggest that you believe the incident actually happened. Could you provide some more evidence in support of that belief?

My skepticism is based on descriptions of the original attempts at electrocution where vastly more energy than is possible here did not kill the victims, the survival of people with vastly more current through their hearts from lightning strikes, the lack of specifics in the claim put forth, the lack of a credible source for the story, and my general understanding of what it takes to kill somebody from electrical shock. All of this could be leading me to an incorrect conclusion which I will quite happily reconsider in the face of contradictory evidence.

As to the capacitance issue: I didn't understand your point. My point was that the energy required to charge the capacitance of the human body to nine volts was vastly insufficient to be an issue with regard to electrocution. The human body is routinely charged to and discharged from static electricity without serious damage. In very dry environments the human body can reach a potential approaching 30,000 volts and to my knowledge no individual has suffered more than painful annoyance during a discharge event.
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Old 21st November 2012, 04:26 AM   #33
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Originally Posted by davefoc View Post
OK, that is your right to decide that. Your post seems to suggest that you believe the incident actually happened. Could you provide some more evidence in support of that belief?
I don't care if the incident actually happened. Making your inquisition to my belief of that incident as irrelevant as your assertion of disbelief to that incident.

Originally Posted by davefoc View Post
My skepticism is based on descriptions of the original attempts at electrocution where vastly more energy than is possible here did not kill the victims, the survival of people with vastly more current through their hearts from lightning strikes, the lack of specifics in the claim put forth, the lack of a credible source for the story, and my general understanding of what it takes to kill somebody from electrical shock. All of this could be leading me to an incorrect conclusion which I will quite happily reconsider in the face of contradictory evidence.
Ah, your skepticism, a different matter indeed. Of the event itself or just the physical and physiological parameters involved? I certainly do understand your stated basis of skepticism for just the potential of such an event. As you assert the energy involved. Voltage is a representation of the energy it takes to move a charge. More specifically it is the work that has to be done to move a charge in a static electrical field. However, it's not so much the work as where the work is done. Across your heart such electrical work can cause more problems then across your finger. A man I worked with got the tip of his finger burned off (and his arse knocked of a ladder) at just 240 volts. Fortunately that circuit to ground did not include his heart. All it takes, as noted before, is enough amperage to disrupt the heart at the right time, and with sufficient amperage across the heart (or anywhere), timing ain't gon'na help you.


Originally Posted by davefoc View Post

As to the capacitance issue: I didn't understand your point. My point was that the energy required to charge the capacitance of the human body to nine volts was vastly insufficient to be an issue with regard to electrocution. The human body is routinely charged to and discharged from static electricity without serious damage. In very dry environments the human body can reach a potential approaching 30,000 volts and to my knowledge no individual as suffered more than painful annoyance during a discharge event.
If you look at the video I posted most recently. The two workers are charged to a transmission potential (over 100 kV) and the helicopter then discharged as it leaves. So the ability of the human body to obtain some (well at least electrical) potential is not in dispute.
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Old 22nd November 2012, 01:27 AM   #34
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Originally Posted by The Man View Post
...



If you look at the video I posted most recently. The two workers are charged to a transmission potential (over 100 kV) and the helicopter then discharged as it leaves. So the ability of the human body to obtain some (well at least electrical) potential is not in dispute.
The issue here is the capacitance of the human body and whether it can be charged or discharged quickly enough to cause substantial damage or death. The video you posted demonstrates the idea that something can be charged up to a large voltage and if everything else is at the same potential there won't be a problem.

I don't quite know what in my posts you have taken offense to other than that I expressed skepticism of the story about the sailor that died as a result of electrocution from a nine volt battery. I don't know why you would take offense at that. If I am wrong you can post evidence of my wrongness or you can just enjoy the inner glow of knowing that you are right. Either way it doesn't seem that I have insulted you and if I have or you believe I have I can tell you unequivocally that this was not my intent.
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Old 22nd November 2012, 11:19 AM   #35
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Originally Posted by davefoc View Post
The issue here is the capacitance of the human body and whether it can be charged or discharged quickly enough to cause substantial damage or death. The video you posted demonstrates the idea that something can be charged up to a large voltage and if everything else is at the same potential there won't be a problem.
Once again the ability of the human body to reach some potential is not in dispute so that is specifically not issue here. That was the point of the video to show that it is simply not a issue. As what you claim is "The issue here" simply and specify is not, do you have any other issues of concern?

Originally Posted by davefoc View Post
I don't quite know what in my posts you have taken offense to other than that I expressed skepticism of the story about the sailor that died as a result of electrocution from a nine volt battery. I don't know why you would take offense at that. If I am wrong you can post evidence of my wrongness or you can just enjoy the inner glow of knowing that you are right. Either way it doesn't seem that I have insulted you and if I have or you believe I have I can tell you unequivocally that this was not my intent.
I have taken no offense and I'm sorry that I can not help what you might try to read into what I have written. Again your fixation on whether that particular story happened or not is irrelevant. If you have some questions or problems with the physical and physiological parameters involved we can discuss them if you can try to specifically articulate them.

Let me try to clarify, the ability, or lack thereof, of the human body to reach some potential does not in and of itself place a significant potential difference across ones heart. In fact being at an equal potential is the result thus minimizing potential differences. It is when there is a potential difference across the heart that a disruptive current can flow. That's the key aspect of the story (not whether it actually happened or not) that the blood as an electrolyte can apply that full potential difference directly across the heart and not a matter of charging or discharging the human body.

Once again I'm sorry if anything I have written gave you the impression of offense or that you perhaps think I might have some interest in you being wrong. I'm just trying to lead you to the relevant aspects and it's not if the story actually happened or the capacitance of the human body. I'm more than happy to discuss any relevant issues you may want to discuss but there is simply nothing for us to discuss on matters of no relevance other than for me to try to show again the lack of relevance. Naturally if you do have some questions about the capacitance of the human body that is something we can discuss as long as you do understand that it has no relevance to a voltage being applied directly across the heart (as in the case of the story related).
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Old 26th November 2012, 06:19 PM   #36
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I do apologize again if my remarks seemed offensive, but misinformation about the human body and it's interaction with electrical fields gets people hurt or killed. So I'll lay it out again, the two independent variables are applied voltage and resistance thus determining current (or charges moved per unit time). The other element (as mentioned before) is circuit pathways. A circuit has two "poles" attach to just one or the other and you've got no problem. You will be charged to that potential. When you make a path between both and when that path includes your heart that's when you've got problems. Heck with the guy I worked with it still wasn't a path through his heart (fortunately) just through the tip of his finger that he lost, at least he has the chance to remember that.
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Old 26th November 2012, 08:27 PM   #37
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to add for capacitance

In the last video I posted you will note that they extend a wand to the line that you see an arc jumping. Air (our atmosphere) is a dielectric or insulator that can be polarized (a critical element in a capacitor) the arcing is the breakdown of that dielectric. Again you will see the breakdown of that air dielectric as the helicopter leaves and is discharged. The two points being that it is a controlled charge and discharge (by the wand) and that it is a breakdown of the air (as the dielectric in a capacitor) that is controlled to accomplish the job without injury to the workers or damage to the helicopter.
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