The air we breathe on airplanes and pressurization

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In this new installment we will learn about the air we breathe on airplanes and how the pressurization system of the aircraft.

Post written by: Captain Rudolph Star
FAA Commercial Pilot
Twitter: @rodo_estrella

At the end of last September, a news was presented on CNN where the title was put "A scary moment in the air: a Delta plane went down 9.000 meters suddenly.

A sensational title so you have to demystify regarding how the plane works, your environmental system, pressurization and because maneuvers are sometimes necessary that can cause fear.

The air we breathe

To understand how the pressurization and air conditioning systems of an aircraft work, We first have to know the air that we normally breathe in the environment and the effect it has on our body when there is a condition of lack of oxygen..

The normal ambient air that we all breathe at any time is subject to an atmospheric pressure, This pressure exerted on all bodies is greater at sea level and less in places like Quito or La Paz., high altitude cities.

We have heard that oxygen is less at high altitudes but it is incorrect, Throughout the atmosphere the percentage of oxygen is constant at about 21%, the difference is that the concentration of this is lower per parcel of air thanks to lower atmospheric pressure.

Imagine a parcel of air 1 square meter, at sea level it will have the full weight of the atmosphere on it, Although we believe that this weight is not felt, this exists, The weight of the atmosphere is caused by the force that planetary gravity exerts on all things including the air and the atmosphere., this weight at sea level makes the oxygen particles more concentrated and therefore there are many oxygen particles concentrated in said plot, these oxygen particles are more stuck to each other so to speak, but if we take this parcel of air to a much higher altitude, the weight of the atmosphere above it is less so there is less atmosphere above it exerting pressure, that causes the oxygen particles to be exposed to a lower pressure and that causes a lower oxygen concentration, the particles expand causing that in that same parcel of air its concentration of oxygen is lower.

Then, An airplane flying at very high altitudes would cause the concentration of oxygen in the air to be very low in the passenger cabin, producing an effect known as hypoxia in its occupants..

Hypoxia in general features is a condition of lack of oxygen in the body, At higher altitudes, the body's response to remain conscious is drastically reduced due to lack of oxygen, reaching a very few seconds when altitudes exceed 35.000 O 40.000 pies. But its first effects can be observed at much lower altitudes from 10.000 O 12.000 pies.

Eventually being exposed to this oxygen deprived condition leads to death as we all know that the human body needs oxygen to live..

Then, how is it that we can fly so high and be able to breathe on the plane? Very easy, It's because of the pressurization system..

Pressurization

The pressurization system is a system that provides the pressurized section of the aircraft, that is, the room or rooms that will be occupied by people or living beings an air pressure equivalent to a lower altitude, in this way the oxygen concentration is set at a level at which the occupants can breathe normally.

How is pressurization achieved??

Not all systems are the same and they vary in their operation from plane to plane., but generally the system consists of obtaining pressurized air from the turbine engines to “fill” the cabin.

This air comes from the section or also called the compression stage of a turbine engine., where air is taken from the environment and by means of compressors it is compressed to feed the following phases of turbine power, In the middle of these clean air compression stages there are the so-called "bleeding valves" that extract part of that hot compressed air and redirect it through filters and pressure regulator systems towards the cabin..

This high pressure air is regulated to provide a simulated "atmospheric" pressure in the cabin equivalent to a pressure from a much lower altitude. This air is known as pressurized air..

This effect of introducing higher pressure air into the aircraft cabin produces a force on the fuselage, a force that struggles to get out, therefore, the emergency doors are plug type and in flight no matter how much force one exerts they cannot be opened because to open them inwards one has to overcome the pressurizing force exerted on it.

It should be noted, the closer the plane is to the ground, in descent for example, the internal pressure approaches the external pressure, opening the possibility of an emergency door, could be physically opened in flight.

Then, this air that leaves the engines enters hot, since one effect of applying pressure to an air mass is to increase its temperature for that reason it would result in a pressurized but uncomfortably hot cabin, so the system mixes this hot air with cold outside air to regulate its temperature or an air conditioning system works together.

Clean Air

The air that enters the cabin for pressurization is not like that of a balloon that inflates and stays that way all the time.. All the air that enters is in constant circulation and temperature modulation, that is, it will always be fresh. And the system is kept constantly pressurized with fresh air.

In the pressure bulkheads located usually in the rear there are regulating valves that maintain the selected cabin pressure and maintain a flow of exhaust air, as well as there are safety valves that act in case of failure of the regulating valves and allow to depressurize if necessary or keep the plane depressurized on the ground.

Usually the passenger feels that the air has a strange atmosphere, sometimes it can even smell, this is because the air comes from the motors, goes through filters, regulators, circulation channels, grids, etc. where it collects impurities from the system but as mentioned above, since it comes from a clean section of the engine there is no danger of it being contaminated air.

emergencies

Returning to the case of the Delta flight, now that we know how the pressurization system works and how it provides us with a cabin that gives us the comfort of being able to breathe easily with high air pressure, we must also think that since it is a system, this is prone to fail at any time.

Then, what happens if the system fails or if there is a depressurization in the cabin?

For these cases there are emergency procedures, where the crew's priority is to descend to an altitude at which all occupants can breathe normally, for this you must proceed with an emergency descent, Apparently it may seem like a dangerous procedure, but the maneuver is normal and very necessary..

The first thing we will have as passengers is the presentation of oxygen masks, These temporarily provide oxygen to breathe normally, but these masks do not have a sufficient amount of oxygen for the entire duration of the flight, so it is a priority to take the plane to a lower altitude where the concentration of oxygen allows normal breathing since, as already It was mentioned that the time of consciousness at high altitudes without oxygen is a few seconds, so we proceed to descend as quickly as possible, generating that feeling of “dread” in the passengers, however, it is a normal procedure and very necessary to avoid damage to the health of the occupants..

Now that we know how pressurization works, the environmental system and what happens if these fail we are sure that if at any time we have to face an emergency of this type, we will know how to act calmly, knowing that the crew is doing everything possible for the immediate well-being and health of everyone and by staying calm you can even help other passengers to stay calm.

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