Voltage can kill

[groman]

@Chefguy

I’m confused, however, cuz back then you told me (rather irritably) that it was indeed the voltage and not the amperage. In this thread, you seem to contradict that. S’plain?

Imagine getting killed by being shot in the head by a 10 gram lead bullet traveling at 300 meters per second. Now, is it the velcotiy of the bullet that kills you or the weight? Obviously if a 10 gram bullet was going a lot slower it wouldn’t hurt you, or if a nanogram bullet was going 300 meters per second it wouldn’t really hurt you either, but the combined momentum of 10 grams at 300 meters per second is quite lethal. Now, for bullets you can alter the two variables relatively independantly, yes it takes more energy to accelerate a heavier bullet, but most numbers are possible.

For electricity the two numbers depend on the entire circuit, including you in it.

[Chefguy]

@Crafter_Man

Chefguy:

I know it seems confusing, but my position hasn’t changed.

In that thread you said,

I was focusing more on the “90v vs. 120v is irrelevant” comment than anything else. I pointed out that voltage is important in the sense that you need enough voltage to produce the lethal amount of current.

Let me try again.

It’s all based on Ohm’s Law:

V = IR

where

V = Voltage across the body (volts)
I = current through the body (amps)
R = resistance of the body (Ohms)

Medical researchers have “calibrated” the lethality of electricity in terms of I (current through the body). They have determined that the risk of death greatly increases when the current is above 0.06 amps.

So here’s the question: How do you get the current to be greater than 0.06 amps through the body?

Answer: V/R > 0.06

If V/R > 0.06, then the risk of death greatly increases.

Based on the equation V/R > 0.06,

If R is very high (e.g. current enters & exits through thick, clean, dry skin), then you need quite a bit of voltage for electrocution.

If R is fairly low (e.g. current enters & exits through broken skin), then a low voltage can cause electrocution.

Does that clear it up?

I like Chronos’ explanation better, as it seems intuitively more correct.

[Arjuna34]

@Chronos

I think it’s safer (from a pedagogal point of view, at least), to just point out that voltage, current, and resistance are inextricably tied together, and leave it at that. You can’t blame the voltage or the current separately unless you could change one variable without changing the other two, and you can’t do that.

To make it even more inextricable, human body impedance actually is voltage-dependant in a non-linear way. There are many complex mechanisms in the skin which depend on voltage. Skin resistance drops dramatically at around 50V.

Here’s a very good paper on it: Step and Touch Voltage (especially starting at page 9).

It goes without saying that the actual resistance varies with skin contact area, moisture content, mechanical pressure, etc.

On top of that, body impedance also varies with frequency!

Arjuna34