# What kills people current or voltage?

Uneducated people often say "It's the current that kills, not the voltage", but this is a myth. Current cannot flow without voltage to push it.

While it's possible for a low voltage 12 V car battery to drive hundreds of amps of current through a wrench and cause the wrench to melt or the battery to explode, it's harmless to put your hands across the terminals of a car battery. Why? Because your skin's resistance is far higher than the wrench's. Even though car batteries can produce high current under certain conditions, it's not possible for a low voltage source to drive a high current through a human.

(That doesn't mean you shouldn't be careful around car batteries. Anything that can release large amounts of energy is dangerous, whether a current source or a voltage source, but in the case of car batteries, it's only a danger of explosions or burns; they can't harm you electrically.)

The myth may have started because static electricity (like scuffing feet across a carpet) builds up thousands of volts, and the discharge obviously isn't harmful. Again, the myth is wrong. The harmlessness of static shocks is not due to low current. They're actually relatively high current: several amps. The reason static shocks are harmless is because they are extremely short in duration. The amps of current only flow for a fraction of a microsecond, which isn't enough time to cause any damage.

The current through the heart is what kills you. It only takes a few milliamps to disrupt the heartbeat. (About 15mA for men and 10mA for women, though this varies from person to person.)

Your body has resistance, and it is very high. This is why high voltage is dangerous, low voltages cannot cause the amount of current to flow that is deadly. High voltages can. Remember ohms law here: V = IR where V is voltage, R is resistance, and I is current. What to know how much voltage will kill you? Take a ohmmeter and hold one lead in each hand, then multiply the reading by 0.025 (25mA).

Electrical burns are from power dissipation in your body. This is a product of both voltage and current. As the voltage forces the current through you, the resistance in you causes power dissipation. This power builds up has heat and burns you. Remember the formulas: P = IV and V = IR, so P = V2/R.

To summarize, current is what messes you up, and it is a function of voltage.