Now I get it 
my dry skin safe me
But sweat just a little and you’re toast…
Electricity tends to kill you in two different ways.
The first way is that it screws up your heartbeat. Hit the heart with a shock at just the right time, and it will go into fibrillation, where it just sits there and shakes and isn’t pumping blood. Our heart has kind of a funny design in that this fibrillation state is stable, meaning that the heart generally won’t go out of fibrillation on its own once you get it there. Since the heart isn’t pumping blood, you pass out in a few seconds (maybe 10 to 15 seconds tops) and then die a few minutes later. Better hope there is someone nearby with a portable defibrillator.
It takes a surprisingly small amount of current to throw the heart into fibrillation. Electrical standards in the U.S. are generally based around currents under 5 mA being “safe”, though not a lot of human testing has been done to confirm this for ethical reasons that I hope should be obvious. The numbers are based more on animal studies than human guinea pigs.
Even though a 5 mA current can theoretically kill you, it’s not very likely to. As the current increases, so does the risk of fibrillation, up until you get around the 50 to 100 mA range mentioned upthread, at which point the risk of fibrillation is much more severe. Fibrillation is kinda hit and miss though. Your heart is much more sensitive to disruptions at certain times during its cycle than others, so there’s a lot of luck involved with the timing of exactly when the shock hits your heart.
A funny thing happens as you increase the current though. At higher current levels, the heart doesn’t go into fibrillation. Instead, all of the heart muscles just clamp. At that point the heart isn’t pumping blood, so again you will pass out and die if the source of the current isn’t removed. However, once the current is removed, the heart generally goes back into a normal rhythm.
As you keep increasing the current, you start getting into the second way that electricity kills you. It literally cooks you to death. This is how the electric chair kills you. It’s also how lightning usually kills you. There’s a wicked amount of energy in a lightning bolt - hundreds of millions of volts and hundreds of thousands of amps. At those extremes, lightning becomes very weird and unpredictable. The electric chair is pretty much always fatal, and that’s only a few thousand volts (over a much longer duration). Lightning, even with its bizarrely high voltages and currents, will sometimes fry you to a crisp and will sometimes leave you relatively unscathed.
So overall, what happens is that as you increase the current (generally by increasing the voltage), the fatality rate starts off near zero, the rises, then drops for a bit as you get into the range of the heart clamping, then rises again as you get into heat damage.
While it is true that it’s the current that matters in this case, voltage and current aren’t exactly unrelated. All other things being equal, a larger voltage will result in a larger current. All other things are not always equal though.
The “resistance” of the human body varies. Humans aren’t simple ohmic resistors. A commonly used model of the human body is a resistor in series with a resistor and capacitor in parallel, but the values of those components varies depending on the circumstances. At low voltages, the “resistance” will be several k to several megs. At higher voltages, the “resistance” of the body drops to somewhere around 500 to 1000 ohms, which is a pretty significant difference.
I’ve heard about someone killing themselves with low voltages (like 3 to 6 volts from batteries, somewhere in that range) by using something that stuck needles or probes into their skin. It might just be an electrical urban legend though as I’ve never been able to confirm it.
It could, but you’d probably need to have the electrical contacts pierce your skin to overcome your skin’s resistance. Generally speaking, you need to get somewhere in the range of 50 volts or so before the voltage will overcome your skin’s resistance and the resulting current starts to get dangerous.
Skin resistance may save your heart but you’ll probably sustain very bad burns. Though I’d take that over cardiac arrest.
There is an ancient (no cite) story of a US Navy recruit in training to be an Electrician.
One day, they were issued volt/ammeters and had a discussion about safety, including the fact that human skin was actually a pretty decent insulator.
At this point, for those who don’t know - the instrument has a small battery used to place voltage across a circuit to measure resistance.
This is the set-up. Pondering the question of skin and resistance, the story goes, he poked small holes in his index fingers, and placed the leads in the holes to measure the resistance of human meat.
The voltage (from a tiny battery, 9v ‘transistor’ batteries, for instance) passed through his heart.
As mentioned above, it takes virtually no current to stop a heart - esp. when those are pure DC (as from batteries).
My Q: anyone have a cite for this story of volt meter killing an inquisitive Electrical student in the USN?
Yep. And it is not possible (at least right now) to calculate how many volts is necessary to achieve 100 mA or whatever.
In order to determine the voltage necessary to achieve a certain current through the body, we would need an accurate electrical model of the human body. Such a model does not exist at this time.
The human body cannot be modeled as a simple resistor. Or a resistor & capacitor. Furthermore, the current in the human body is not due to mobile electrons but mobile ions. Scientists have spent the last hundred years studying the electrical impedance of saltwater in the lab, and they still don’t have a good handle on it.
So when it comes to voltage and the human body, about the best you can do is go by some rules-of-thumb. ECG brought up one: voltages less than 50 V are *generally *considered safe, for *most *people, in *most *circumstances, *most *of the time.
Through, not across!
Voltage is across, current is through.
Remember that a sharp blow to the chest at just the right spot and the right time can stop the heart, but it’s a rare occurrence. I’m sure most electrocutions involve higher voltages and currents, and probably AC. There have been plenty of electricians who tested for hot wires by touching them, and a friend of mine who works for National Grid on the heavy power lines says he doesn’t even care about household electricity because even 240 volts isn’t going to kill him. I’d be a little more cautious myself, but it’s an indication of how rare electrocutions are under normal circumstances.
The large capacitor has enough energy to electrocute by affecting the heart electrochemistry…
It also has enough energy to cause painful burns to the skin, and cramp up your biceps and other muscles… This cramping can then have serious results… eg disabling injury to muscles… tear something (muscle,ligament, joint tissues, break a bone ), pinch a nerve, wry neck…
Worse, if you are working near exposed mains power, you might then be touching mains power… repeat for other dangers (even the floor is a danger… if you fall over and bang your head on it… falling over rotating fast enough to hit head first… )
This is basically what I was referring to in the last line of my post #23 above.
I’ve heard several variants on this story. The most common is that it was an electrical technician of some sort, sometimes in the USN, sometimes not. The other variant that I’ve heard was that it was some sort of device used for sexual pleasure, and not a meter. The key in every version though is that the skin was somehow punctured in order to overcome the skin’s resistance.
I’ve never been able to confirm any version of this story, which is why I’m wondering if this is an electrical urban legend.
This is the USN version, commonly known because it has been passed around as a Darwin award.
From here: 1999 Darwin Award: Resistance is Futile
Note that the Darwin Awards page lists it as “unconfirmed”.
Darwin Awards, aka “funny stories people made up”.
how people can survive after million volts go through the body
People survive getting shot, too.
Were you part of this thread? Your input would be perfectly on point (and an excuse to zombifie it is always welcome):
How many people connected in series to power a lightbulb?
This sounds like the beginning of a joke, but, given GQ standards, it’s deadly serious.
There’s a sole 60-watt light bulb that must be turned on for a minute or everyone will die of fear of darkness. You have insertable single head-plugs, luckily made of lithium, and you have a ton of connection wire. The head of each plug is 2 centimeters in radius.
You decide everyone must chip in and give their electroconductive best, and be plugged in in series to generate their share of amps. How many people would be needed to save the day?
It should really be Ohm’s general observation. Most complex things like say biological tissue do not obey Ohm’s law very closely. It is a lot like Hook’s law springs only Obey Hook’s law over a smallish range.
Rare, medium-rare, medium, or well done?
My father had an old anecdote about a college prof who used to charge up a Leyden jar (those were the days) and demonstrate resistance in series by having the students stand in a circle holding hands and he and the other end of the circle would touch the opposite contacts of the jar, and everyone would feel a slight tingle. Then to demonstrate the RC constant effect, he would drain the remaining charge by holding the one contact with his finger and touching the other contact close to his nose for a small visible spark.
One clever student heard about this demonstration beforehand and persuaded the fellow next to him not to hold hands… Then, after the RC demonstration, when the prof regained consciousness…
seven times in head?
…pausing only once to reload…