How deep can a human go before pressure kills them?

Pressure itself does not crush a body, because tissue is mostly incompressible water — the problem is what pressure does to gases. Breathing air at depth pushes nitrogen into solution, producing narcosis with judgement loss from around 30 metres and rising sharply beyond 60, and oxygen itself becomes toxic and can cause seizures below about 60 metres on air. Ascending too fast lets dissolved gas come out of solution as bubbles, which is decompression sickness. Commercial saturation diving avoids the ascent problem by keeping divers at depth pressure for weeks in a chamber, breathing helium-oxygen mixtures; the record chamber depths reached in the Comex Hydra trials were 534 metres in the sea and around 700 metres simulated, where high-pressure nervous syndrome — tremor and confusion — became the limiting factor. Competitive freediving reaches beyond 200 metres on one breath, where the chest compresses to a fraction of its surface volume.

What changes the figure

• Helium-oxygen mixtures remove nitrogen narcosis and are what make deep diving possible
• Ascent rate, not depth, causes decompression sickness
• The limit at extreme depth is neurological, not structural

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 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 much electricity can a human survive? Current decides it, not voltage — around 100 milliamps through the chest can stop the heart.
• 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.