Cabin pressure in aircrafts

Posted on March 3, 2008. Filed under: Uncategorized |

Cabin pressure in aircrafts

If cabin pressure wasn’t required, you could have a good open-window view during flights and people would fight for window seats! (not that they don’t do it now, it’ll just be more). You could, literally, keep your head among the clouds! What if someone decided to open a window and jump? Oh… what if someone takes their very bad habit of spitting or littering and throw things out…eeks…!!! Ok… slow down there Imagination… all that’s not happening.

Cabin pressure is not for the above mentioned reasons but it works for them too.

When you are around 8,000 ft above sea level, there is about 25% less oxygen. Most people can tolerate the difference without ill effects. If you have heart disease though, you might experience symptoms of hypoxia (shortage of oxygen in the body) even as low as 5,000 ft. As the altitude increases, one might become sluggish or experience unconsciousness.

Aircrafts that fly regularly above 10,000 ft are equipped with an oxygen system. Cabin pressure is maintained by

a)      Using masks or canulas, typically in a smaller aircraft

b)      Using an ECS or an Environment control system. This system uses “bleed air” in which the air extracted from the engine is compressively heated at 200 degrees C and then cooled by passing through a heat exchanger.

Most aircrafts also have a manual back-up system and these systems maintain pressure equivalent to 8000ft or lower even at altitudes above 43000 ft. So what you breath in modern airlines is 50% “outside air” (from the compressed air system) and 50% “filtered air” (from the recirculation fans). There is some truth when they say that the air in the first class is better! Most jetliners supply constant flow per unit length of the cabin. The seats in first class are spaced farther apart, resulting in more air per seat, but the nozzles provide the same amount of air at all locations.

If you are wondering about the queasy feeling and blocked ear (called “aerotitus”) during flights, your answer is here. When an airplane compresses and decompresses, the gases in your body may expand or contract in response. Also, that’s why you have oxygen masks flying down in the event of a pressurization failure.

Now you know why people start flying all over the place when they show a villain firing a hole inside the aircraft. The pressure inside the airplane might be 70 kPa (10 psi), while the pressure outside is only 15 kPa (2 psi). An otherwise-harmless pinhole under these pressure differences will generate a high-pitched squeal as the air leaks out at supersonic speeds. Quite an apt situation to pray to all the Gods you know and even the ones you don’t.

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thats for sure, brother


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