How much radiation can a human survive?
Acute radiation syndrome is a dose-and-rate problem: the same total dose spread over years does something entirely different from the same dose in minutes. Rapidly dividing tissue fails first, so the sequence is bone marrow at 1-6 sieverts, then the gut lining at 6-10, then the nervous system above roughly 20-30 where death follows within days regardless of treatment. Background exposure is around 2-3 millisieverts a year, a chest CT is roughly 5-10 millisieverts, and occupational limits are typically 20 millisieverts a year — all far below the acute range. The commonly quoted median lethal dose is about 4.5 sieverts without medical care; intensive supportive treatment, transfusions and infection control push that figure meaningfully higher. Chernobyl provided the clearest human data: of 134 emergency workers with confirmed acute radiation syndrome, 28 died within months, and survival tracked dose closely.
What happens, in order
| When | What |
|---|---|
| Below 0.5 Sv | No acute illness; measurable blood count changes at the top of the range |
| 1-2 Sv | Nausea and vomiting within hours; bone marrow suppression over weeks; most recover |
| 4-6 Sv | Severe marrow failure; roughly half die without intensive care |
| Above 10 Sv | Gut and nervous system failure; death within days |
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 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.
Common questions
- 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.
Related pages
- 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 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 long can you survive without water? Going without something
- How long can you survive without food? Going without something
- How long can you survive without air? Going without something
- How long could you survive in deep space? Places
- How long can you survive without sleep? Going without something
- Could you survive on Mars? Places