How much electricity can a human survive?

The dangerous quantity in a shock is current through the body, and current depends on voltage divided by resistance — which is why dry, intact skin at hundreds of thousands of ohms turns a household voltage into a nasty shock, while wet skin at a few hundred ohms turns the same voltage into a lethal one. About 1 milliamp is perceptible, around 10 to 20 milliamps causes muscles to contract so hard that the person cannot let go, and roughly 100 milliamps passing through the chest can throw the heart into ventricular fibrillation. Path matters as much as magnitude: hand to hand or hand to opposite foot crosses the heart, hand to same-side foot largely does not. Alternating current at mains frequency is more likely to cause fibrillation than direct current at the same level, and residual current devices exist precisely to cut supply within tens of milliseconds at leakage currents well below the fibrillation threshold.

What happens, in order

Thresholds compiled from published electrical safety standards; outcome depends on current path, duration, frequency and skin resistance.

Physiology, not instruction. Every figure here is a population range under particular conditions, and individual variation is large — temperature, exertion, fitness and health move all of them substantially. Nothing on this page is medical advice.

Conditions

• Can you survive being struck by lightning? Usually, yes — around nine in ten people struck by lightning survive, though many are left with lasting injuries.
• How long can you survive in freezing water? Around an hour before unconsciousness in water near 0 °C — but the first minute is the one that kills most people.
• What happens to your body in a vacuum? You do not explode. Consciousness goes in about fifteen seconds from oxygen leaving the blood.
• How long can you survive in extreme heat? It depends on humidity more than temperature — once the wet-bulb temperature reaches about 35 °C, sweating cannot cool you at all.
• How long can you survive in extreme cold? Hours in still air with dry clothing; under an hour in wind at -30 °C — and people have survived core temperatures near 12 °C.
• How much radiation can a human survive? Below about 1 sievert most people recover; around 4.5 sieverts kills roughly half; above 8 sieverts survival is very rare.
• How long can you survive carbon monoxide exposure? Hours at low concentrations, minutes at high ones — and it has no smell, colour or taste to warn you.
• How long can you survive in a house fire? Around three minutes in a modern room before flashover, and smoke rather than flame is what kills most people.
• How loud does a sound have to be to kill you? Sound alone cannot exceed about 194 dB in air — beyond that it is a blast wave, and blast is what causes injury.
• How deep can a human go before pressure kills them? About 200 metres on a single breath, around 60-70 metres on air, and roughly 500-700 metres in a saturation chamber.
• How much g-force can a human survive? About 4-6 g sustained before blacking out, 9 g in a pressure suit, and over 100 g briefly in a crash.
• How long can you survive in boiling water? No meaningful time. Water at 100 °C causes full-thickness burns instantly, and burns over a large area are fatal.
• How long can you survive at high altitude? Indefinitely up to about 5,500 metres if you acclimatise. Above 8,000 metres the body only deteriorates.
• How long can you survive if an aircraft cabin decompresses? Roughly 30 to 60 seconds of useful consciousness at 35,000 feet — which is why the mask goes on before helping anyone else.