Question

Airplanes are pressurized for the comfort and safety of the passengers and flight crew. Generally, the air pressure in the cabin is equivalent to around \(3000 \mathrm{ft}(915 \mathrm{~m})\), which is a pressure of 686 torr, about \(90 \%\) of that at sea level. A pressurization equivalent to \(8000 \mathrm{ft}(2500 \mathrm{~m})\) would still be safe, with a pressure of 570 torr, about \(74 \%\) of that at sea level. What would happen to the passengers if the aircraft was not pressurized and flew at \(30,000 \mathrm{ft}\) \((9150 \mathrm{~m})\) ?

Short answer

If an airplane was not pressurized and flew at 30000ft (9150m), the lower pressure and oxygen levels would cause the passengers and crew to experience symptoms of altitude sickness such as shortness of breath, fatigue, and potentially severe conditions like pulmonary and cerebral edema. For safety reasons, it is important for aircraft cabins to be pressurized.

Step-by-step solution

Understanding Atmospheric Pressure

Atmospheric pressure is defined as the force exerted by the weight of the air. It reduces with increase in height, as the amount of air above us decreases. At sea level, the atmospheric pressure is about 760 torr.

Effect of Pressure on Human Body

The human body is designed to live in conditions found at sea level, where the atmospheric pressure is 760 torr. As the pressure decreases (or increases) from this level, it can have numerous effects on the human body, such benefits in acclimatization to higher altitudes, or harm, such as altitude sickness, decompression sickness, and hypoxia.

Calculation of Pressure at Different Altitudes

According to given data, pressure at a pressurization equivalent of 3000ft (about 915m) is 686 torr, which is about 90% of the sea level pressure and at 8000ft (about 2500m) it is 570 torr, which is 74% of sea level pressure.

Understanding of Pressure at 30000ft without Pressurization

At an altitude of 30000ft (9150m), the pressure is far lower than at sea level. There is less oxygen available to breathe and less pressure to push the oxygen into one's lungs. Without pressurization, the occupants of the aircraft would experience altitude sickness, causing symptoms like shortness of breath, fatigue, and possibly more severe reactions such as pulmonary and cerebral edema.

Key concepts

Aircraft Cabin Pressurization

The concept of aircraft cabin pressurization is critical for maintaining a safe and comfortable environment for passengers and crew at high altitudes. Imagine an aircraft flying at high altitudes without a pressurized cabin; the reduced atmospheric pressure could have severe consequences on human health.

Aircraft are engineered to keep the cabin pressure at levels similar to those found at lower altitudes, typically equivalent to the air pressure at 3000ft to 8000ft above sea level. This controlled environment prevents adverse effects on the body that can occur in the thin air of high altitudes. The pressure inside the cabin is managed by drawing in air from the outside, compressing it, and then maintaining it at a specified level, which facilitates easier breathing and adequate oxygen absorption by the body.

Altitude Sickness

Altitude sickness, also known as acute mountain sickness (AMS), generally occurs when people rapidly ascend to high altitudes where the air pressure is low and there is less oxygen available. Symptoms include headache, fatigue, dizziness, nausea, and trouble sleeping.

If an aircraft were not pressurized, as mentioned in the textbook exercise, flying at 30,000ft could lead to altitude sickness as the pressure drops significantly compared to sea level. The human body is highly adaptive, but a swift transition to high altitudes can fail to give the body enough time to adjust, resulting in the various symptoms associated with AMS. Preventative measures usually include gradual ascent, acclimatizing to intermediate altitudes, and, in the case of aircraft, ensuring appropriate cabin pressurization.

Hypoxia

Hypoxia occurs when the body doesn't get enough oxygen to function properly and it can happen rapidly at high altitudes where the atmospheric pressure is low and oxygen levels are reduced.

At sea level, where the pressure is about 760 torr, our bodies are well-suited to absorb oxygen effectively from the atmosphere. At the cruising altitude of an airliner, however, without cabin pressurization, the oxygen levels could drop to the point where the body's tissues and brain do not receive enough oxygen. Symptoms of hypoxia include breathlessness, palpitations, dizziness, and a bluish color on the skin. In the cabin of a pressurized aircraft, the potential for hypoxia is mitigated by maintaining the internal pressure at an equivalent to an altitude where sufficient oxygen is available for the body.

Decompression Sickness

Decompression sickness, often associated with divers, can also occur in aviation if the cabin depressurizes too quickly. This condition is caused by the formation of nitrogen bubbles in the blood and tissues, which happens when the pressure surrounding the body decreases too rapidly.

In an unpressurized aircraft at 30,000ft, the rapid decrease of atmospheric pressure would cause these nitrogen bubbles to form, leading to joint pain, dizziness, headache, fatigue, and other symptoms. Aircraft cabin pressurization systems are thus very important to prevent such a rapid change in pressure. Moreover, modern aircraft are equipped with safety measures, including oxygen masks that deploy if the cabin pressure drops, to offer immediate protection against the effects of decompression sickness.