Cabin Pressurization

What is Cabin Pressurization?

Cabin pressurization is the active pumping of compressed air into an aircraft cabin when flying at altitude to maintain a safe and comfortable environment for crew and passengers in the low outside atmospheric pressure.

Pressurization is essential over 3,000 metres (9,800 ft) to protect crew and passengers from the risk of hypoxia and a number of other physiological problems in the thin air above that altitude and increases passenger comfort generally. "The outflow valve is constantly being positioned to maintain cabin pressure as close to sea level as practical, without exceeding a cabin-to-outside pressure differential of 8.60 psi." At a cruising altitude of 39,000 feet (FL 390), a Boeing 767's cabin will be pressurized to an altitude of 6,900 feet.[1]

Possible sickness

When the aircraft lost its' pressure crew and passengers are at risk from hypoxia, altitude sickness, decompression sickness and barotrauma.


The lack of oxygen into the lungs and subsequently in the brain leading to sluggish thinking, dimmed vision, loss of consciousness and ultimately death. In some individuals, particularly those with heart or lung disease, symptoms may begin as low as 1,500 metres (4,900 ft) above sea level although most passengers can tolerate altitudes of 2,500 metres (8,200 ft) without ill effect. At this altitude, there is about 25% less oxygen than there is at sea level. Hypoxia may be addressed by the administration of supplemental oxygen, usually through an oxygen mask sometimes through a nasal cannula.

(Video embedded from YouTube on 01 Octuber 2009)

Altitude sickness

The low local partial pressure of carbon dioxide (CO2) causes CO2 to out-gas from the blood raising the blood pH and inducing alkalosis. Passengers may experience fatigue, nausea, headaches, sleeplessness and on extended flights even pulmonary oedema. These are the same symptoms that mountain climbers experience but the limited duration of powered flight makes the development of pulmonary oedema unlikely. Altitude sickness may be controlled by a full pressure suit with helmet and faceplate, which completely envelopes the body in a pressurized environment; this is clearly impractical for commercial passengers.

(Video embedded from YouTube on 01 Octuber 2009)

Decompression sickness

The low local partial pressure of gases, principally nitrogen (N2) but including all other gases, may cause dissolved gases in the bloodstream to precipitate out resulting in gas embolism or bubbles in the bloodstream. The mechanism is the same as for compressed air divers on ascent from depth. Symptoms may include the early symptoms of the diver's bends: tiredness, forgetfulness, headache, stroke, thrombosis subcutaneous itching but rarely the full symptoms of the bends. Decompression sickness may also be controlled by a full pressure suit as for altitude sickness.


As the aircraft climbs or descends passengers may experience discomfort or acute pain as gases trapped within their bodies expand or contract. The most common problems occur with air trapped in the middle ear (aerotitus) or paranasal sinuses by a blocked Eustachian tube or sinuses. Pain may also be experienced in the gastrointestinal tract or even the teeth (barodontalgia). Usually these are not severe enough to cause actual trauma but can result in soreness in the ear that persists after the flight and can exacerbate or precipitate pre-existing medical conditions such as pneumothorax (collapsed lung). The following video is on barotruma on bats as they flew through wind turbines.

(Video embedded from YouTube on 01 Octuber 2009)


Pressurization is when aircraft is keeping its pressure at a safe psi when the outside altitude and pressure is far lower and colder. This is to substain life on board the flight and to give comfort to human live. When pressurization is not done properly, there will be a drastic lost of pressure and a number of illness will set in to hinder human life.

1. Wikipidia - Cabin pressurization (2009) Retrieved from Wikipidia on 01 Oct 2009
2. How Things Work: Cabin Pressure (2002) Retrieve from How Things Work on 01 Oct 2009

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