---
title: "How much radiation can a human survive?"
description: "Below about 1 sievert most people recover; around 4.5 sieverts kills roughly half; above 8 sieverts survival is very rare. What actually happens physiologically, in "
url: https://atoneplace.net/could-you-survive/radiation/
site: "At One Place"
---

# How much radiation can a human survive?

**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.**

Weeks for doses in the 1-6 sievert range; days for doses above about 10 sieverts

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?](https://atoneplace.net/could-you-survive/lightning-strike/) — 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?](https://atoneplace.net/could-you-survive/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?](https://atoneplace.net/could-you-survive/vacuum/) — You do not explode. Consciousness goes in about fifteen seconds from oxygen leaving the blood.
- [How long can you survive in extreme heat?](https://atoneplace.net/could-you-survive/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?](https://atoneplace.net/could-you-survive/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?](https://atoneplace.net/could-you-survive/carbon-monoxide/) — 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?](https://atoneplace.net/could-you-survive/fire-smoke/) — 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?](https://atoneplace.net/could-you-survive/extreme-noise/) — 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?](https://atoneplace.net/could-you-survive/high-pressure-depth/) — 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?](https://atoneplace.net/could-you-survive/g-force/) — 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?](https://atoneplace.net/could-you-survive/electric-shock/) — Current decides it, not voltage — around 100 milliamps through the chest can stop the heart.
- [How long can you survive in boiling water?](https://atoneplace.net/could-you-survive/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?](https://atoneplace.net/could-you-survive/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?](https://atoneplace.net/could-you-survive/cabin-decompression/) — 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?](https://atoneplace.net/could-you-survive/lightning-strike/)
- [How long can you survive in freezing water?](https://atoneplace.net/could-you-survive/freezing-water/)
- [What happens to your body in a vacuum?](https://atoneplace.net/could-you-survive/vacuum/)
- [How long can you survive in extreme heat?](https://atoneplace.net/could-you-survive/extreme-heat/)
- [How long can you survive in extreme cold?](https://atoneplace.net/could-you-survive/extreme-cold/)
- [How long can you survive carbon monoxide exposure?](https://atoneplace.net/could-you-survive/carbon-monoxide/)
- [How long can you survive in a house fire?](https://atoneplace.net/could-you-survive/fire-smoke/)
- [How loud does a sound have to be to kill you?](https://atoneplace.net/could-you-survive/extreme-noise/)
- [How long can you survive without water?](https://atoneplace.net/could-you-survive/without-water/)
- [How long can you survive without food?](https://atoneplace.net/could-you-survive/without-food/)
- [How long can you survive without air?](https://atoneplace.net/could-you-survive/without-air/)
- [How long could you survive in deep space?](https://atoneplace.net/could-you-survive/deep-space/)
- [How long can you survive without sleep?](https://atoneplace.net/could-you-survive/without-sleep/)
- [Could you survive on Mars?](https://atoneplace.net/could-you-survive/mars/)

## Sources

- World Health Organization — WHO (https://www.who.int/)