The voltage a human can withstand depends primarily on the current that flows through the body, which is influenced by both the voltage and the body's resistance. Voltage alone does not determine lethality; it is the current (amperage) passing through vital organs, especially the heart, that causes fatal injuries.
Key Points on Voltage and Human Tolerance
- Threshold voltage: Generally, voltages above 50 volts can drive a potentially lethal current through the human body because the body's resistance can be overcome to allow dangerous current flow
- Body resistance: The human body's resistance varies widely depending on skin condition and environment:
- Dry skin: up to 100,000 ohms or more
- Wet or sweaty skin: around 1,000 ohms
- Submerged in water: as low as 150 ohms
This means that the same voltage can cause very different currents depending on these conditions
- Lethal current levels:
- Currents as low as 7 mA (0.007 amps) can be fatal if they pass through the heart for a few seconds.
- Around 100 mA (0.1 amps) almost certainly causes death due to ventricular fibrillation.
- Even 10 mA can cause severe muscle contractions and inability to release an electrified object, increasing danger
Voltage Examples and Effects
- A 9V battery is generally harmless because it cannot push enough current through the skin.
- Household voltages (e.g., 120V or 240V AC) are dangerous and can be lethal because they can push sufficient current through the body, especially if skin is wet or broken
- High voltages above 500 volts increase the risk of severe burns, cardiac arrest, and death.
- Extremely high voltages (thousands of volts and above) are usually fatal, but there are rare cases of survival with severe injury
Summary
- The human body can withstand voltages up to about 50 volts safely under normal dry conditions.
- Above 50 volts, the risk of lethal current flow increases significantly.
- The actual danger depends on skin resistance, contact points, duration of exposure, and the path current takes through the body.
- Fatal electric shocks can occur at surprisingly low voltages if conditions allow enough current to pass through the heart.
In conclusion, while voltage is a factor, it is the current driven through the body by that voltage, modulated by body resistance and exposure conditions, that determines how many volts a human can withstand. Typically, voltages above 50 volts are potentially lethal under certain conditions
