Being at high altitude poses significant risks to human health and survival. As elevation increases, the air pressure decreases, meaning there is less oxygen available to breathe. Oxygen is essential for the body and brain to function normally. Without adequate oxygen levels, you may develop a condition called hypoxia, which can rapidly become life-threatening.
What happens to the body at high altitude?
The higher you climb in elevation, the lower the air pressure becomes. For example, at sea level the air pressure is around 760 mmHg, while at 18,000 feet (5,500 meters) it drops to only 380 mmHg. This decrease in pressure means there are fewer oxygen molecules in each breath you take. At 18,000 feet, there is only about half as much oxygen in the air compared to sea level.
As the body detects less oxygen, it responds by increasing breathing and heart rate to take in more oxygen. However, if the lack of oxygen is severe, you may develop altitude sickness with symptoms like headaches, nausea, fatigue, and trouble sleeping. Without treatment, altitude sickness can progress to potentially fatal conditions like high altitude pulmonary edema (fluid buildup in the lungs) and high altitude cerebral edema (fluid buildup in the brain).
| Altitude (feet) | Oxygen level | Health effects |
|---|---|---|
| Sea level | 21% | None |
| 8,000 | 15.5% | Mild hypoxia possible |
| 12,000 | 12.8% | Moderate hypoxia likely, acute mountain sickness possible |
| 18,000 | 10.5% | Severe hypoxia, high altitude illnesses likely |
Exposure to very high altitudes above 25,000 feet (7,600 meters) is fatal no matter how much supplemental oxygen is provided. This is known as the “death zone” where oxygen levels are not high enough to sustain human life.
How long can you survive at high altitude?
How long someone can survive at a given high altitude depends on several factors:
- Rate of ascent – Climbing to altitude too quickly increases risk of altitude sickness and fluid buildup.
- Altitude reached – The higher the elevation, the lower the oxygen and shorter time one can survive.
- Individual variation – Some people are more susceptible to altitude’s effects.
- Acclimatization – Allowing time for the body to adjust can increase tolerance.
- Supplemental oxygen – Access to extra oxygen improves survival duration.
At altitudes above 25,000 feet, supplemental oxygen is necessary for survival. Even with extra oxygen, durations longer than 48 hours are unlikely. Without it, loss of consciousness can occur within minutes and survival time may be as short as 10-20 minutes.
In the “death zone” above 26,000 feet, mountaineers typically can only spend a matter of hours at most with supplemental oxygen before deteriorating health forces descent. Most experts consider survival above 25,000 feet unsustainable beyond two days even with extra oxygen.
Survival times at extreme altitude
| Altitude | With supplemental oxygen | Without supplemental oxygen |
|---|---|---|
| 18,000 feet | Days to weeks | Hours to days |
| 22,000 feet | Days | Minutes to hours |
| 26,000 feet | Hours | Minutes |
| 29,000 feet | Minutes to hours | Minutes |
As shown, survival times rapidly diminish above 22,000 feet without supplemental oxygen. Even with extra oxygen, durations longer than a few days at these extreme elevations are unlikely.
How to survive at high altitude
Here are some tips to survive at high elevation for longer durations:
- Ascend slowly – Gradual ascent allows the body to acclimate to the lack of oxygen.
- Stay hydrated – Dehydration exacerbates altitude sickness symptoms.
- Avoid alcohol – Alcohol can increase fluid loss and affect judgment at high altitude.
- Monitor symptoms – Headaches, nausea, and fatigue are signs to descend immediately.
- Take it easy – Rest and avoid strenuous exercise to minimize oxygen demand.
- Use supplemental oxygen – Portable oxygen systems can prolong survival at extreme elevations.
- Descend if needed – Evacuate to lower elevation if altitude sickness develops.
Medications to prevent and treat altitude sickness
Certain medications can also improve high altitude survival by preventing and treating altitude sickness:
| Medication | Effects |
|---|---|
| Acetazolamide | Reduces symptoms of AMS and HAPE by increasing ventilation |
| Dexamethasone | Relieves cerebral edema and symptoms of severe AMS |
| Nifedipine | Dilates pulmonary vessels to treat HAPE |
| Salmeterol | Bronchodilator that can reduce HAPE risk |
While these medications can be helpful, they are not substitutes for descent when severe altitude illness develops.
Conclusion
Human survival at high altitude is limited by the lack of sufficient oxygen. Above 25,000 feet, supplemental oxygen is necessary for more than brief durations. Exactly how long someone can survive also depends on the rate of ascent, altitude reached, individual variation, and degree of acclimatization. Gradual ascent, hydration, rest, and medications can prolong survival, but immediate descent is the only definitive treatment for severe altitude sickness.