Pressurization of aircraft at high altitudes is necessary to maintain a sufficient level of oxygen on board, allowing passengers and crew to breathe normally and prevent the harmful effects of low atmospheric pressure, such as hypoxia.
At high altitude, the air becomes quite thin and its pressure drops, which significantly reduces the amount of oxygen available. Our lungs struggle to capture enough oxygen at these altitudes, quickly causing discomfort, intense fatigue, or even loss of consciousness. Pressurization allows for a sea-level-like atmosphere to be replicated in the airplane. How? A portion of the compressed air from the engines is taken, cooled, and then sent into the cabin to maintain a proper and stable pressure. Without this, it would be impossible to fly comfortably without risking one's health.
At high altitudes, the air is less dense and its pressure drops, which results in a decrease in the amount of oxygen available. Less oxygen in the blood quickly becomes problematic for the body. The first symptoms? Often dizziness, nausea, and that infamous persistent headache. Gradually, this hypoxia causes vision disturbances, slower reflexes, difficulties in reasoning, and sometimes even mild euphoria. In short, we lose our judgment capacity without necessarily realizing it. Higher up, without a secure supply of oxygen, it quickly becomes critical: loss of consciousness, irreversible brain damage, or even death over time. On top of that, the rapid drop in pressure can cause ear pain due to improper equalization of the internal and external pressure of the eardrums. The sinuses can also become inflamed or blocked, which is not very pleasant. As a result, without a pressurized cabin, even the strongest do not last long up there.
Without pressurization at high altitude, air becomes extremely rare, dangerously reducing the amount of oxygen available for the body. As a result, there is a risk of rapid hypoxia: the brain slows down, leading to loss of consciousness in just a few minutes and, in the worst-case scenarios, rapid death. Another major concern: the sudden drop in pressure can cause explosive decompression, resulting in severe injuries and even risking a breach in the aircraft's structure. On top of that, temperatures plummet drastically; without a pressurized cabin, you literally freeze at altitude, with temperatures potentially reaching up to -50°C. One last nice detail: low pressure also increases the risk of altitude sickness, with symptoms like severe migraines, nausea, and disorientation. In short, flying without pressurization is far from a leisurely stroll.
The pressurization of civil aircraft is subject to specific rules to ensure the safety of passengers. The ICAO (International Civil Aviation Organization) provides the guidelines, adopted by most member countries. For example, cabin pressure must correspond to an altitude of less than 2400 meters to avoid risks related to lack of oxygen. In the United States, it is the FAA (Federal Aviation Administration) that sets its own standards, often aligned with international standards. Aircraft must have an emergency system in case of rapid decompression, such as the famous oxygen masks. Airlines are strictly required to regularly check their pressurization systems during periodic technical maintenance.
Modern airplanes mainly use a pressurization system based on air drawn from the compressors of jet engines. This hot, compressed air then passes through coolers to achieve a pleasant temperature in the cabin and maintain a comfortable pressure for passengers and crew. A device called a regulation valve continuously adjusts the internal pressure by expelling excess air to the outside. This allows the fuselage of the aircraft to remain at a higher pressure than the very low-density outside air at high altitude.
Recent airplanes like the Boeing 787 Dreamliner use a different approach with systems known as electrical pressurization. These systems avoid the direct use of engine air, providing more precise control of humidity and increasing cabin comfort. Less fatigue, less dehydration, and an overall more pleasant feeling during long-haul flights. Thanks to these technological advances, today's pressurized cabins ensure safety and comfort for thousands of passengers every day.
The windows of commercial airplanes are rounded not only for aesthetic reasons but, more importantly, because this shape distributes the stresses related to pressure more effectively, thereby reducing the risks of cracks or catastrophic failures.
At an altitude of 10,000 meters without a pressurized cabin, loss of consciousness generally occurs in less than a minute due to lack of oxygen. This is known as hypobaric hypoxia.
In the event of rapid decompression of an aircraft, you only have a few seconds to put on your oxygen mask before hypoxia affects your reaction time—hence the importance of listening carefully to the safety instructions before the flight!
The Boeing 787 Dreamliner features an innovative pressurization system that maintains a cabin altitude significantly lower (around 1,800 meters instead of 2,500 meters for conventional aircraft), thus greatly enhancing passenger comfort.
The cabin of an airplane flying at an altitude of approximately 10,000 to 12,000 meters is usually pressurized to a level equivalent to an altitude of about 1,800 to 2,500 meters, ensuring a comfortable oxygen level for passengers and reducing the risks of hypoxia.
An average individual can breathe unassisted up to about 2500 to 3000 meters in altitude. Beyond this altitude, the air gradually becomes too thin in oxygen, making effective breathing difficult and jeopardizing physiological functions.
In the event of rapid decompression, the oxygen masks will deploy automatically. It is crucial for passengers to put on these masks immediately, as at high altitudes, the amount of available oxygen is insufficient, quickly leading to hypoxia, a potentially fatal condition. The pilots will also initiate a rapid descent to a lower and safer altitude as soon as possible.
The sensation of blocked ears results from rapid variations in atmospheric pressure with altitude. The inside of the middle ear, a closed space containing air, usually equilibrates through the Eustachian tube. However, during a rapid change in altitude, this tube sometimes fails to equalize the pressure quickly enough, creating the characteristic sensation of blocked ears.
A cabin that is inadequately pressurized can cause altitude-related issues or hypoxia in passengers and crew, leading to headaches, confusion, shortness of breath, or loss of consciousness in severe cases. If not addressed quickly, this situation poses serious health risks and even threatens the survival of passengers.
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