How long can you survive carbon monoxide exposure?

Carbon monoxide binds to haemoglobin roughly 200 to 250 times more readily than oxygen does, so it displaces oxygen from blood and holds on. The result is suffocation with normal-looking breathing: the person feels headachy, nauseated and confused rather than short of breath, because the reflex that makes you gasp responds to carbon dioxide, not to missing oxygen. Symptoms are easily mistaken for flu, and because judgement is affected early, people often fail to leave. Concentration decides the pace: a few hundred parts per million causes headache and confusion over one to two hours, while several thousand parts per million produces unconsciousness within minutes. The only reliable warning is an audible carbon monoxide alarm, because none of the human senses detect it at all.

What happens, in order

What changes the figure

• Working alarms on every level of a home are the only practical detection
• Fresh air and, in serious cases, high-flow or hyperbaric oxygen speed clearance from the blood
• Children, pregnant people and those with heart disease are affected at lower concentrations

If a carbon monoxide alarm sounds, the correct response is to leave the building and call emergency services from outside.

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 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.