why do oxygen masks drop in planes
Most that operate at high flight altitudes are pressurized at a maximum cabin altitude of approximately 8,000 feet. On most pressurized aircraft, if cabin pressurization is lost when the cabin altitude is above 14,000 feet, compartments containing the oxygen masks will open automatically, either above or in front of the passenger and crew seats, and the oxygen masks will drop down in front of the passenger. Oxygen masks may also drop on extremely rough landings or during severe turbulence if the oxygen mask panel becomes loose. Rows of seats typically have an extra mask (i. e. 3 seats, 4 masks), in case someone has an infant in their lap, or someone in the aisle needs to grab one. An oxygen mask consists of a yellow, soft, silicone facial cup with white elastic bands for securing the mask to the passenger's face. This band is adjustable by pulling two ends looped through the facial cup. The mask may also have a concentrator or re-breather bag that may or may not inflate depending on the cabin altitude, which has (in some instances) made passengers nervous the mask was not providing adequate oxygen, causing some to remove them, who thereby suffered hypoxia. All airlines now make a point in the safety video or demonstration to point out that the bag may not inflate. The bag is attached to a tube, connected to the oxygen source in the compartment, allowing for it to drop down and hang in front of the passengers.
To operate on all aircraft except the, they must be pulled sharply toward the passenger who needs it to un-clip the flow pin and start the process of transporting the oxygen to the passenger. Passenger oxygen masks cannot deliver enough oxygen for sustained periods at high altitudes. This is why the flight crew needs to place the aircraft in a controlled emergency descent to a lower altitude where it is possible to breathe without emergency oxygen. While the masks are being used, passengers are not allowed to leave their seat for any reason until it is safe to breathe without the emergency oxygen. If there is a fire on board the aircraft, masks are not deployed, as the production of oxygen may further fuel the fire. and shown at the beginning of each flight explain the location and use of oxygen masks. Some aircraft, such as the SAAB Series Aircraft and the 1900D, have a mask system where either a mask is stored under the seat or is distributed by the cabin attendant. These masks are removed from packaging and plugged into the socket for oxygen supply.
Before any airplane takes off, the cabin crew gives a brief demonstration about the various safety procedures that passengers need to follow in case of an emergency. In my opinion, the most interesting part of that short demo is the brief intro of oxygen masks that are enclosed in chambers above our seats, designed to drop down if the cabin suddenly loses air pressure.
Those masks help passengers breathe for a few minutes in a depressurized cabin. The question is: where do they get the oxygen from? Do commercial airplanes carry a huge tankВ of oxygen just in case such an emergency occurs? Short answer: In most commercial airplanes, there is a chemical oxygen generation system, wherein pulling down an oxygen mask removes a firing pin, which initiates a chemical reaction that produces oxygen as a byproduct. You might already know that air pressure as altitude increases. Past a certain altitude above the surface of Earth, the air becomes too thin to remain breathable. In most commercial jets, if the cabin pressurization is disturbed above an altitude of 14,000 feet, panels containing oxygen masks pop open automatically and multiple oxygen masks drop down above/in front of the passengers seats. Typically, aircraft designers put an extra mask per row for contingencies, so a row with 3 seats will have 4 masks. Note that these masks are NOT required to be worn by passengers for the entire timeВ until the plane lands. They provide oxygen only for a short time, during which the pilots sacrifice the aircraft s altitude and descend to a safe zone where the outside air becomes breathable once again.
The crew might also announce вmasks offв to let people know that they have descended to the breathable part of the atmosphere and that they no longer need oxygen masks to breathe. Where do oxygen masks get their oxygen from? One might think that airplanes carry a huge scuba tank onboard and that all the oxygen masks are connected to it. In the case of cabin depressurization, the tank could be switched on to supply oxygen to the crew and passengers. Similarly, it could be shut off once the plane has descended to a safe altitude. That way, you could also conserve the unused oxygen. That does sound a like a pretty sensible way to supply oxygen to passengers during emergencies, doesnвt it? However, thatвs not how it happens in reality. Breathable oxygen is not stored in tanks onboard airplanes; instead, itвs produced as a result of a chemical reaction. Airplanes contain oxygen generators, commonly known as oxygen candles, which contain certain chemicals that give off oxygen gas a byproduct. The candles generally consist of sodium chlorate (NaClO-3), less than 5% barium peroxide (BaO-2) and less than 1% potassium perchlorate (KClO-4). This mixture is activated by the application of heat, which is provided through the activation of a small explosive charge (yes, a very small explosion actually gets the chemical reaction going).
But what sets off the charge? Have you ever paid attention to the fact that, during the safety demonstration, they actually advise you to tug on the oxygen mask? This is because when you tug on it, the firing pin that holds back the charge is released, kick-starting the chemical reaction. The chemicals burn and release oxygen gas as a byproduct, which is channeled to your nose through a pipe (after filtering out other byproducts). Since the chemicals practically burn during the reaction, itвs highly likely that one might sense a burning smell, which could cause panic amongst passengers. However, itвs perfectly normal and is in no way a safety risk to the plane. The reaction goes on until the chemicals are exhausted. So, once the mask is pulled, it can provide breathable oxygen for 12-20 minutes, depending on the type and size of the oxygen generator. At any rate, you only need the вmask oxygenв until the plane descends to 10,000 feet, asВ the surrounding air will become breathable again from that point on. The main takeaway from all of this is quite simple В if you ever happen to be in an aircraft that experiences cabin depressurization, donвt panic! Just tug on the oxygen mask, put it your nose and remember chemistry has got you covered!
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