What's the Highest Altitude a Human Can Survive?

Imagine standing on the roof of the world, where the air is thin and the temperature bites with icy teeth. How high could you go without the aid of technology before your body starts to fail? The answer is more complex than you might think, involving a delicate balance of oxygen levels, acclimatization, and the sheer will to survive.

The Oxygen Threshold

As you ascend, the concentration of oxygen molecules decreases, leading to a state called hypoxia. Altitude sickness begins to manifest around 5,000 feet (1,500 meters) above sea level. At this height, your body struggles to obtain enough oxygen, resulting in:

Increased breathing rate
Muscle fatigue
Difficulty sleeping

These symptoms worsen as you climb higher.

Around 8,000 feet (2,500 meters), these symptoms can escalate to:

Dizziness
Headaches
Nausea
Vomiting

These are indicators of Acute Mountain Sickness (AMS), which is generally not life-threatening and subsides upon descent.

The Physiological-Efficient Zone

Beyond 10,000 feet (3,000 meters), you enter a danger zone where the risk of developing High Altitude Cerebral Edema (HACE) and High Altitude Pulmonary Edema (HAPE) increases. These conditions involve fluid accumulation in the brain and lungs, respectively, and can be fatal without prompt treatment.

Environmental Challenges

Above this altitude, temperatures typically plummet below freezing, increasing the risk of frostbite. The body prioritizes core temperature, diverting blood flow away from extremities, making them vulnerable to the cold.

At 16,000 feet, you might face temperatures as low as -17ºC (2ºF). Despite these harsh conditions, the highest permanent human settlement, La Rinconada, Peru, exists at 16,700 feet (5,100 meters), inhabited by 50,000 to 70,000 people.

La Rinconada: A Testament to Human Endurance

In La Rinconada, each breath contains only half the oxygen available at sea level. Residents survive due to:

Larger lung capacities
Efficient oxygen utilization

These adaptations, whether genetic or acquired through long-term exposure, enable better sleep and exercise performance. However, Chronic Mountain Sickness affects a significant portion of the population, leading to an excessive increase in red blood cells, potentially causing heart failure and death. The only cure is to descend to a lower altitude.

The Limits of Permanent Habitation

The highest recorded altitude for permanent human tolerance is 19,520 feet (5,950 meters). In 1935, a scientific expedition found that a Chilean miner, Justo Copa, lived at this altitude for two years. Any higher, and the side effects became unsustainable for extended periods.

Entering the Death Zone

Above 26,000 feet (8,000 meters) lies the Death Zone, where the oxygen deficit is so severe that the human body begins to deteriorate and die. Climbers ascending to Everest's summit (29,029 feet / 8,848 meters) require acclimatization and supplemental oxygen to survive the approximately 7-hour journey.

Acclimatization: Preparing the Body

Acclimatization allows the body to increase its hemoglobin levels, enhancing oxygen absorption. This process involves gradual ascent with stops at different altitudes over weeks or months. However, even with acclimatization, most climbers rely on oxygen bottles above 23,000 feet.

The Elite Few

Some elite climbers have summited Everest without supplemental oxygen, but they represent only a tiny fraction of successful ascents and a disproportionately large percentage of deaths in the Death Zone.

Beyond Everest: The Absolute Limit

Professor Mike Grocott estimates that the limit of human survival without extra oxygen is around 9,000 meters (29,527 feet), slightly above Everest's summit. But what about ascending via balloon into the stratosphere?

Above 49,000 feet (15,000 meters), the pressure is so low that supplemental oxygen becomes ineffective. Carbon dioxide is removed from the blood faster than it is produced, leading to alkalosis and potentially fatal damage to proteins.

The Armstrong Limit

Above 60,000 feet (18,000 meters), the Armstrong Limit is reached, where the boiling point of fluids drops to the average body temperature. This causes surface fluids in the mouth, eyes, and lungs to vaporize. Survival at this altitude requires specialized pressure suits or pressurized cockpits.

The Armstrong Limit, named after Harry G. Armstrong, is considered the absolute limit of human survival, although variations in body temperature can cause effects as low as 55,000 feet (17,000 meters).

In conclusion, human survival at extreme altitudes is a complex interplay of physiological adaptation, environmental conditions, and technological assistance. While the exact limits may vary, the challenges and risks are undeniable.