Significance Of Altitude

Survival:
The human body needs oxygen to survive. Of the three main necessities of life (air, water, and cheese burgers), oxygen is the most critical. This is highlighted by the survival Rule of Threes. In any extreme situation you cannot survive for more than:

• 3 minutes without air
• 3 days without water
• 3 weeks without food

What is the link between oxygen and altitude?
In simple terms, the higher you go, the less oxygen there is. We get oxygen from the atmosphere which is a large mass of air that is several miles thick. The weight of all that air, at sea level, is roughly equivalent to 30 feet of water. Because air is compressible, the weight of the air above you compresses the air around you, thus creating higher air or barometric pressure. As you go up in altitude,there is less air above so the air around you becomes less compressed therefore decreasing the barometric pressure.(http://www.altitude.org/why_less_oxygen.php)