How long can you survive in extreme cold?

Air is a poor conductor of heat, so still, dry cold is survivable for far longer than most people expect — the enemies are wind and water. Wind chill at -30 °C with a strong wind can freeze exposed skin in under ten minutes, and wet clothing loses most of its insulating value and can shorten survival time by a factor of several. Hypothermia progresses through recognisable stages: shivering and clumsiness below a core temperature of 35 °C, confusion and loss of shivering below 32 °C, and unconsciousness with a barely detectable pulse below 28 °C. Cold has one strange property: it slows metabolism so much that people have been resuscitated from core temperatures that would otherwise be fatal, including a documented case at 13.7 °C after a skiing accident and a young child at 11.8 °C. This is why cold-water and avalanche casualties are not declared dead until they have been rewarmed.

What happens, in order

What changes the figure

• Dry clothing and a wind barrier matter more than total thickness
• Alcohol feels warming and actively accelerates heat loss by dilating skin vessels
• Insulation from the ground prevents a large share of conductive loss

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 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 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.