At 40,000 feet, your time of useful consciousness is just a few seconds without pressurization. Here's how airplane cabins are pressurized to keep you safe and comfortable.

A Brief History Of Pressurization

In the early days of aviation (we're talking balloons in the 1700-1800s), pressurization was largely ignored. Aeronauts of the time simply didn't understand the effects of low pressure, high altitude environments on the human body.

In 1875, three French aeronauts attempted a high altitude ascent in a Zenith balloon. At 26,000 feet, all three lost consciousness, and only one survived. By 1931, a pressurized cabin was attempted for the first time in a gondola suspended beneath a balloon. Finally, in 1939, the first high altitude passenger aircraft with a pressurized cabin was developed, the Boeing 307 Stratoliner.

Pressurizing An Aircraft's Cabin Has Multiple Benefits

There are four primary goals to keep a comfortable and safe cabin for passengers, maintaining: temperature, humidity, air circulation, and cabin pressure. Most pressurized cabins are designed for aircraft operating at service ceilings between 25,000 - 50,000 feet. Inside these aircraft, the pressure of the cabin generally falls somewhere between 6,000 - 8,000 feet in cruise flight at high altitudes.

Here are a few important benefits pressurization provides:

• Oxygen masks don't need to be worn
• Low risk of decompression sickness
• Less noise and vibration
• Better control of temperature
• Better air ventilation
• Fewer trapped gas problems (physiologically)



Mechanics Of Pressurization

Ambient air is introduced into a compressor, which is usually the airplane's engine. As the air is compressed, it heats up rapidly. This heated air is sent through a cooling unit, like a fuel-air heat exchanger. Through ducting, this air is then introduced into the cabin.

A series of over-flow or outflow valves regulate how quickly air is released from the cabin. Air comes into the cabin quicker than it's released, creating a high-pressure cabin environment.

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There are a few types of pressurization systems:

• Isobaric: The most common system, where cabin pressure is maintained at a constant value regardless of the outside air pressure.
• Isobaric Differential: Military fighter aircraft begin pressurization on ascent until the cabin reaches a pre-set altitude. If the altitude is reached, a constant pressure differential is maintained in correlation with the ambient pressure outside the airplane.
• Sealed Cabin: Used in spacecraft only, where the vessel carries its own supply of gases.



New Aircraft Lower The Bar, In A Good Way

The Boeing 787 and Airbus A350 are two great examples showing improvements being made to traditional pressurization systems. While the overall concept of pressurization in commercial aircraft hasn't changed all that much in the past 50 years, the cabin altitudes have.

Both of these aircraft are rated to a maximum cabin pressure of 6,000 feet. That's substantially better than the 7,500-8,500 feet you'll find in older jets. On long flights, this prevents passengers from experiencing negative health effects from high-altitude environments... Even helping to reduce the impact of jetlag.

Ken Mist

Loss Of Pressurization: What Happens When Things Go Wrong?

Now that you have a firm understanding of pressurization, you should know there's a lot that can go wrong with these systems. A depressurization event is a serious, potentially life-threatening emergency. Stay tuned for an article coming soon which will break down the most common abnormal and emergency situations regarding cabin pressure.

What do you want to learn in our upcoming articles? Tell us in the comments below.

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