Could you survive?

70 questions about what the body and the environment actually do. These are physiology pages — they describe what happens, not how to bring it about, and every figure is a range rather than a limit.

The rule of threes is a mnemonic, not a rule

Three minutes without air, three days without water, three weeks without food. It is roughly right and genuinely useful for remembering the order of priorities, but every one of those figures moves enormously with temperature, exertion and individual health. Treat it as a ranking of what to solve first, not as a countdown.

Things widely believed that are wrong

• You do not explode in a vacuum. You lose useful consciousness in about fifteen seconds from hypoxia; the danger is decompression, not bursting.
• Quicksand does not pull you under. It is roughly twice as dense as you are, so you float — typically at about waist depth.
• Drowning is usually silent and nearly motionless, not the thrashing and shouting films depict. That is why it is missed.
• Around ninety per cent of people struck by lightning survive it.
• A rip current pulls you away from shore, not down. Swimming parallel to the beach gets you out of it.

Going without something

• How long can you survive without water? About three days in mild conditions — but under a day in desert heat, and up to a week at rest in the cold.
• How long can you survive without food? Weeks rather than days — one to three weeks is typical, and water runs out long before calories do.
• How long can you survive without air? Consciousness goes in about a minute and brain injury begins around four to six minutes.
• How long can you survive without sleep? No one has died of sleep deprivation alone; the record is 11 days, and severe impairment arrives within two.
• How long can you survive without food and water? About three days — water sets the limit and food barely enters into it.
• How long can you survive without sunlight? Indefinitely, provided vitamin D comes from food or a supplement — sunlight itself is not a requirement.
• How long can you survive without human contact? Indefinitely in the direct sense — but isolation measurably raises the risk of dying early.
• How long can you survive without gravity? Indefinitely with exercise countermeasures — the record for one continuous flight is 437 days.
• How long can you survive without salt? Weeks to months at rest — kidneys are very good at conserving sodium — but days if you are sweating heavily.
• How long can you survive without vitamin C? Scurvy appears after roughly one to three months of near-zero intake, and is fatal in a few months more.
• How long can you survive without protein? Months, because the body cannibalises its own muscle — which is exactly why it eventually kills you.
• How long can someone with type 1 diabetes survive without insulin? Days. Missing insulin in type 1 diabetes is an emergency, not an inconvenience.

Places

• How long could you survive in deep space? About fifteen seconds of consciousness, and roughly ninety seconds before the damage becomes irreversible.
• Could you survive on Mars? Unprotected, under two minutes. In a pressurised habitat, indefinitely — the limits become supply and radiation.
• How long can you survive in the death zone on Everest? Hours to a couple of days. Above about 8,000 metres the body deteriorates no matter what you do.
• How long can you survive adrift in the open ocean? In warm water with a raft, three to five days without drinking water — but immersion in cold water is measured in hours.
• How long could you survive on the Moon? About fifteen seconds of consciousness without a suit. With one, the record stay is 75 hours.
• How long could you survive in the Mariana Trench? Unprotected, no measurable time at all — the pressure is over a thousand times atmospheric. In a submersible, as long as the life support lasts.
• How long can you survive in Antarctica? Minutes to an hour unprotected in a winter storm — or indefinitely, since around a thousand people overwinter there every year.
• How long can you survive in the Sahara Desert? Around a day without water in summer daytime heat, and several days if you can stay in shade and move only at night.
• How long could you survive on Venus? Seconds. The surface is 465 °C at ninety-two times Earth's atmospheric pressure — the hardest place in the solar system to land on.
• Could you survive on Jupiter? There is no surface to survive on — you would fall inward until pressure and heat ended it, within minutes.
• How close to the Sun could you survive? Nothing solid survives contact — but a shielded spacecraft has flown within about 6 million kilometres of the surface.
• How long could you survive on a desert island? Fresh water decides it. With a spring or reliable rain, years; without, about three days.
• How long can you survive on the International Space Station? Indefinitely while it is resupplied — it has been continuously crewed since November 2000.
• How long can you survive in the Arctic? Hours unprotected in winter — but roughly four million people live above the Arctic Circle permanently.
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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 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.
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Situations

• Can you survive a plane crash? Usually — across all US airline accidents studied, more than 95 per cent of occupants survived.
• How long do you have to escape a sinking car? Usually 30 seconds to a couple of minutes of floating — and the window is the way out, not the door.
• Can quicksand pull you under? No. Quicksand is roughly twice as dense as a human body, so you float — you sink to about waist depth and stop.
• How far from a nuclear blast do you have to be to survive? It scales with yield: for a one-megaton airburst, survival is unlikely within about 5 km and likely beyond about 10-12 km.
• How long can you survive in a hot car? Under an hour on a warm day for a child — the interior gains about 20 °C in the first ten minutes.
• How long does it take to drown? Under a minute to lose consciousness — and it is almost silent, which is why so many drownings happen in sight of others.
• What happens if a lift cable snaps? Essentially nothing — lifts hang from multiple ropes and have a speed-triggered brake that grips the rails.
• What height can you survive falling from? Survival is common below about 6 metres and rare above 20 — but people have survived falls from thousands.
• How likely are you to survive a shark attack? Very likely — of roughly 60 to 80 unprovoked bites worldwide each year, fewer than ten are fatal.
• What happens if you fall into lava? You would not sink — lava is about three times denser than a body — but you would not survive the heat either.
• What should you do if you are caught in a rip current? Rips pull you out, not under. Swim parallel to the beach until you are out of the flow, then come in.
• Could you survive inside a whale? You cannot be swallowed by almost any whale — their throats are too narrow — and a stomach offers no air.
• How long do you have to escape a burning house? Around three minutes from the alarm sounding in a modern furnished home.
• Can you survive a tsunami? Yes, by moving inland and uphill immediately — 30 centimetres of moving water can knock an adult off their feet.
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Physiology, not instruction, and not medical advice. If you are in danger or in crisis, contact your local emergency number — a reference page is not the right place to be looking.