# What is fatal? Current or voltage? [duplicate]

I have been searching this answer for quite a while. I asked my physics teacher and he said it is current that causes death. A friend of mine, who is a EE student, and his answer was voltage. When i searched the internet i read that if the voltage is high then the current is high, so you die. But what if the resistance is so big that even if the voltage is huge the current is small?

So which one?

## marked as duplicate by ACuriousMind♦, Alfred Centauri, Brandon Enright, Qmechanic♦Nov 20 '14 at 23:20

• This question appears to be off-topic because it is about the biological effect of electrical currents/voltages. – ACuriousMind Nov 20 '14 at 22:46
• possible duplicate of What kills you: Voltage or Electric current? – Alfred Centauri Nov 20 '14 at 22:49
• Sorry, I thought since the question is labeled as soft-question, it could be answered. – George Smyridis Nov 20 '14 at 22:49
• Looking back at past related questions we get back to physics.stackexchange.com/q/32484 which is about shock to the body rather than fatality. So though related I wonder if this is a distinct question. – tom Nov 20 '14 at 23:07
• When you boil it down, everything is physics. If you migrate this to biology you might come up short-handed for a good response. You need both camps of knowledge. Voltage is potential, the ability to drive current. If the part of your body that's subjected to the potential has high resistance then a smaller amount of current will flow relative to if you were to wet the skin. It's the current that kills - > 30 mA through the cardiac muscle. – docscience Nov 21 '14 at 0:22

I think the range of answers you have got from friend, teacher and web reflect that there is not a straightforward response.

Without high voltage it would not be possible to drive the dangerous current through the body, but high voltage itself is not lethal - it depends how much current can be delivered at high voltage. Another question is how high does the voltage need to be to be dangerous?

In fact, high voltage can be beneficial to the body.... A number of medical devices use plasmas driven by high voltage. For example, here is a link to a commercial device for surgery. The plasma, driven by high voltage, can be used in surgery to remove tissue and at the same time it cauterizes to prevent excessive blood loss. It is a plasma scalpel effectively.

So the medical device is safe to use because it is high voltage, but low current (it also uses RF or pulsed DC I think, which helps reduce the current but maintain high voltage).

The real danger is high voltage and high current. But then how high is a dangerous high voltage when a large current can be delivered? Maybe over 200 V? Maybe over 120V? (don't try this at home please). The plasma medical device may use a thousand volt. So compared to this medical device dangerous voltages of 200 V or 500 V may be considered medium (or even low) voltage.

Final point, because we are thinking about human bodies we know that the resistance is high, but not very high. Pure water can have very high resitance, but the fluid in our bodies generally has some ions dissolved in it so the resistance will never be as high as something like pure water.

• Statements like "But then how high is dangerous high voltage? Maybe over 200 V?" are misleading and over simplify. You could charge a capacitor to hundreds of thousands of volts and shock the hell out of yourself with a tiny current (because very little charge is stored in the capacitor). – Brandon Enright Nov 20 '14 at 23:06
• @BrandonEnright good point - I hope it was clear though in that paragraph that we are thinking about high voltage with high current -- I will edit to make clearer – tom Nov 20 '14 at 23:09