High-voltage low-amperage current through the human body

[fawk3s]

I=V/R, so the amperage is determined by the voltage and the resistance of the human body, right?
But yet it is possible to have a high voltage but low amperage current go through you, say you grabbing 2 electrodes which have the a high voltage between them. How come the amperage is low and doesn't kill you, but the higher the voltage the more it hurts?

Thanks in advance,
fawk3s

 

[berkeman]

I=V/R, so the amperage is determined by the voltage and the resistance of the human body, right?
But yet it is possible to have a high voltage but low amperage current go through you, say you grabbing 2 electrodes which have the a high voltage between them. How come the amperage is low and doesn't kill you, but the higher the voltage the more it hurts?

Thanks in advance,
fawk3s

The dry epidermis (outer layer of your skin) has relatively high resistance, so that will help to limit the current.

If your hands are sweaty, or if you use electrodes with good coatings (or abrade the epidermis), that gives you lower resistance access to the core of the body, and the core of the body has much lower resistance than the dry epidermis.

 

[schip666!]

Careful when you try this experiment... High-voltage fairly-low current is what is produced by the AED devices used to kick-start arrhythmic hearts...

I think very-low current limiting would be in order, but I don't offhand know what the limit should be. Very low currents may just conduct through your skin and not penetrate the body -- especially if you do not break the skin with the electrodes. Electrical currents probably cause neurons to fire making for pain response, again offhand I'm not sure of the mechanism. They can also create heat leading to burns.

 

[fawk3s]

I can think of a few ways of setting up the circuit where a relatively high voltage would create a low amperage inside your body. But is high voltage necessary for getting killed? Or is there a way a fairly low voltage can cause a high enough amperage to kill you, without your skin being abraded?

 

[berkeman]

Lets be a little careful discussing this, folks. Remember the issue with discussing dangerous activities on the PF...

 

[fawk3s]

Oh no, I aint thinking of trying it out. I am just curious if its possible.

 

[schip666!]

The wiki "Electric Shock" page is illuminating... It says without body penetration 1ma can be felt and 100ma is considered very dangerous. Then this:

If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit though the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case.

and OSHA has a nice summary...who would expect that from a govt agency?

http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html"

 

[RocketSci5KN]

R is a variable, ranging from a very low value (you are mostly a bag of salt water) to a high Megaohm value (dry skin). A high enough voltage can carbonize a path through the skin, leading to an overall low resistance. Enough current through body parts such as the heart or brain can kill you - only a handful of milliamps are enough... There are also current thresholds, the values I don't recall, which make it impossible to 'let go' of a live wire... Obviously, the higher the voltage, the easier it is to get to the dangerous current levels..

 

[fawk3s]

The wiki "Electric Shock" page is illuminating... It says without body penetration 1ma can be felt and 100ma is considered very dangerous. Then this:


and OSHA has a nice summary...who would expect that from a govt agency?

http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html"

Under "Other factors that may affect the severity of the shock" is the voltage of the current.
I still fail to fully comprehend why that is. Amps are what do the damage (as they are under the primary causes of shock on that page aswell) and voltage with resistance are only what determine the amps. So why is "the voltage of the current" brought out separatedly when the only thing it does is determine the amps, which actually do the damage?

Thanks in advance,
fawk3s

 

[schip666!]

So why is "the voltage of the current" brought out separatedly when the only thing it does is determine the amps, which actually do the damage?
fawk3s

I think you've got the idea. Higher voltage means higher current through the same resistance. So one needs to be more careful around higher-voltages. You can grab both terminals of a 12v car battery and probably not feel anything because of the high resistance of your fairly-dry skin.

 

[berkeman]

The wiki "Electric Shock" page is illuminating... It says without body penetration 1ma can be felt and 100ma is considered very dangerous. Then this:


and OSHA has a nice summary...who would expect that from a govt agency?

http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html"

Great info, thanks schip. I'm going to go ahead and close this thread now. The safety warnings in the links above are a good way to end this thread.