The announcement of the flight attendants prior to aircraft takeoff is simple and straightforward: “In case of cabin depressurization, oxygen masks will drop automatically. With the current aviation security parameters, these situations are rare, but the risk always exists. Otherwise you would need the warning before the flight.
The cabin of the plane is like a can of refrigerant gas: there is more pressure inside than outside. So, when the container is opened much of the gas is released quickly. The same effect occurs in the plane suffering a depressurization in altitude from thin air, when cabin pressure equals the atmospheric pressure.
Between 9000 and 12000 metres, altitudes where commercial jets fly, it is necessary to “inject” more cabin pressure in relation to the outside of the aircraft in order to create the conditions so that everyone aboard breathe as if they were on the surface.
If the oxygen pressure is lower than the blood pressure, it’s the so-called “gas exchange”. Put simply, the atmospheric pressure is responsible for “pushing” the oxygen to the blood and blood pressure “kicked out” the carbon dioxide out.
So if there is cabin depressurization at an altitude low pressure oxygen literally enters the bloodstream.
A human being acclimatized can breathe normally at an altitude of up to 6000 meters. After this, what they call the climbers, begins the “death zone”. So who scale the Everest, the highest peak in the world with 8848 meters, takes oxygen cylinders-although a few climbers have already accomplished the climb without auxiliary oxygen.
Wearing the Masks
The plane’s engines pump air into the cabin at all times, maintaining the stable pressure. Depressurization occurs when there is more air leaving than entering the aircraft. This situation can occur due to malfunctioning of the ventilation system or through leaks in the hull. Depending on the case, the pressure loss can be slow or fast.
“A problem of lack of air can only be solved with more air, so when we wear the mask that problem ends immediately,” explains Dan Guzzo, Executive Manager of the company’s operational safety Gol Linhas Aéreas.
When the aircraft’s sensors detect the decompression breathing equipment are triggered automatically. “The masks increase the oxygen concentration, requiring less pressure to breathe,” says Guzzo.
The air we breathe on the surface contains about 20% oxygen in its composition, enough to make the gas exchange in areas of high pressure. With the mask, the concentration rises to 100%, requiring little pressure for absorption.
Contrary to what many think, the oxygen used by passengers in emergencies comes not from canisters hidden in the plane, but rather a chemical reaction. The mask has a “chemical cartridge” called Oxygen Generator, which is located above the boxes in which the shades are stored.
As there passenger pull the mask, which is attached by a drive cable is connected the oxygen generator and a chemical mixture occurs: sodium chloride, barium peroxide and potassium perchlorate combine and release oxygen.
Keep calm, It will end
As soon as the oxygen masks fall, Commander abandons his cruising altitude and descends to around 2000 metres, where you can breathe without the aid of the mask, because the pressure inside the plane is equal to the outside.
“When the depressurization occurs first thing that pilots should do is wear the masks. Then, the Commander asks authorization to the control tower to descend to an altitude where it is possible to breathe normally. When it ends, the crew warns passengers that it is possible to breathe without the masks “, explains the Manager of the Goal.
Depends on the conditions of the aircraft and passengers, it can proceed to their final destination, flying at low altitude, or move on to another airport and perform an alternate landing – which is different from an “emergency landing”.
The oxygen generated by the hard masks 22 minutes in Boeing aircraft. “The descent to the altitude where you can breathe without the masks takes three to five minutes,” reassures Guzzo.
The depressurization of the cabin is more of a scare than a situation in fact dangerous. With the aid of masks and quick action of the pilots, who train these actions in repeatedly simulators, the problem of shortness of breath is quickly resolved.
Who does not put your oxygen mask on time can suffer from the effects of depressurization in just 15 seconds. The main physical symptoms are: fatigue, headache, tiredness, confusion or euphoria, coordination problems, difficulty thinking and vision. So, companies ask first the passengers put on their own masks for only after helping people who can’t do it properly, as children and the elderly.
Other situations that may occur related to cabin pressure of the cabin is the super-pressurização, when there is a defect in the relief valve that releases the excess air, and the explosive depressurization, which consists of a sudden loss of pressure in less than 1000th of a second.
However, as well as the depressurization, these other events are even rarer.
These cases occur due to material fatigue or lack of proper maintenance, something that current aviation does not allow. So keep calm.
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