How Is Cabin Air Recirculated?

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How air onboard an aircraft is circulated is a critical question for those worried about flying during the current crisis. Air circulation onboard commercial aircraft may appear complicated, but it is proven to be cleaner than any other form of transport. Here’s how it works.

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Is the air safe to breathe onboard an aircraft? Photo: Boeing

Where does the air come from?

You might be surprised to learn that an aircraft is not sealed against the atmosphere outside. Cold, fresh mountain air at around -65 degrees from the upper atmosphere enters the plane through the engines (at the compressor stage), called ‘bleed air.’

The system then cools the air to remove the engine heat and pressurizes it to the same level in the cabin, before being mixed with recirculated existing cabin air.

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How is the cabin air recirculated?

Once successfully mixed with the filtered air (we will get to that stage in a minute), the air flows into the passenger compartment from the vents above.

Passengers will breathe the air before it passed back into the system through a series of vents on the floor under the seats. You can find these vents on most aircraft as the point where the wall meets the cabin floor.

The air then passes through a hospital grade filter that removes 99.7% of all biological and pathogen material, before re-entering the cabin mixed with fresh air from outside. Around every three to seven rows becomes compartmentalized by this airflow, meaning that a whole aircraft won’t share the same air throughout a flight at all.

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Then, to maintain pressure, cabin air is also released back into the sky behind the plane. Through this whole process, the atmosphere onboard an aircraft will be ‘refreshed’ on average around 20 times an hour. We can’t say for sure if the air completely refreshes onboard an airplane, but as new air slowly gets added to the aircraft and old air leaked out, it is unlikely that you would land with the same atmosphere pocket.

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You are unlikely to be breathing the same air when you land than when you took off: Photo: LATAM

Can you get sick from cabin air?

Many passengers may think that they are trapped in a small tube breathing the same air as their fellow passengers, but several scientific studies have found that airplane air is some of the healthiest you can breathe.

“There is a heightened risk of infection when you enter a confined space such as an aircraft or subway, but a plane is a much safer place because of the ventilation system,” says Dr. Mark Gendreau, an emergency and aviation medicine expert at the Lahey Clinic in Burlington, Massachusetts, to NBC News in 2010.

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It is not the air that will cause you to have a cold or flu after a flight, but surfaces such as tray tables, cabin bags, TV screens, and armrests can carry harmful bacterial and can cause infection if you don’t wash your hands. Wearing a mask will help prevent you from passing on any viruses through saliva droplets in your breath (that land on surfaces).

As for the feeling of being drained or run down after a flight, this is a combination of jetlag and being in a low-pressure environment for several hours.

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You are more likely to get sick from touching surfaces such as seat headrests and tray tables. Photo: Getty Images

A final note that a study in 2015 has shown that some of the bleed air, if not properly filtered, can contain oil, deicing fumes, or other chemicals from the engines. This is called a ‘fume event’ and is very rare and only dangerous to those who regularly fly, such as pilots and flight attendants. The science is still out if these fumes have long term effects.

What do you think? Let us know in the comments.

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