PHYSIOLOGICAL ZONES OF THE ATMOSPHERE ATMOSPHERIC ZONES


There are 3 main physiological zones in the atmosphere.


The Physiologic [Efficient] Zone extends from sea level to 10,000ft (approx 3,000M) and is the most common zone for air medical flight, specifically rotor-wing (RW) operations. A healthy human being can breathe within this range without requiring additional oxygen.


Overall, the human body operates well in the lower regions of this zone. There may be some minor trapped gas problems (ears, sinus, and GI tract) in the lower parts of the region, while shortness of breath, headaches, dizziness and fatigue will occur in the upper region with prolonged exposure.


The Physiologically Deficient Zone extends from 10,000 to 50,000 ft (3,000-10,000M)


The majority of aviation operations occur in this zone. Exposure to this zone causes severe physiological problems related to the lack of pressure. This is where hypoxia and decompression sickness are concerns.


The Space Equivalent Zone extends beyond 50,000ft


The environment at these altitudes is very hostile to humans. Sealed pressurized environments are the only way to survive. The low pressure will not allow for the transfer of oxygen to the cells and will not support human life.


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ARMSTRONG’S LIMIT


Sometimes it takes a popular event to discover something new about science. A skydive stunt led to the discovery of the now popular Armstrong Limit. The boiling point of water is 100 degrees Celsius only at sea level. However, the boiling point of water decreases as one goes higher due to a decrease in pressure to the point that the boiling point of water at the summit of Mount Everest drops to 71 degrees Celsius. Extending the height means that it reaches a certain altitude where water boils at body temperature. The point where water boils at body temperature is referred to as the Armstrong Limit.


Definition Of The Armstrong Limit


The Armstrong Limit, also referred to as Armstrong’s line, is the height that has atmospheric pressure so low (6.3 kPa) that the boiling point for water equals the normal human body temperature which is normally 37 degrees Celsius. The Armstrong limit begins at an altitude of approximately 60,000 to 62,000 feet. It was discovered by early American aerospace medicine physician, Harry George Armstrong who was the first to realize this occurrence which takes place at an altitude above which no one can survive in the low or unpressurized environment. Armstrong was the founder of the US Air Force Department of Space Medicine.


9 High Altitude Awareness Training


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