How Do Aircraft Oxygen Systems Work?
The oxygen you breathe in the cabin during commercial flights doesn’t come from hulking oxygen tanks, but rather is a pressurized version of the air outside the plane. However, in the case of emergencies, oxygen masks will often drop down that are either filled by way of oxygen canisters or chemical oxygen generators. The design and regulations for these systems can depend on the altitude in which an airplane regularly flies, along with its particular pressurization system or lack thereof. As an essential part of aircraft equipment during emergencies, and even during regular flight on some vessels, it can be vital for aircraft operators and passengers alike to have a general understanding of the various oxygen systems they might encounter.
In a normal situation, a bleed system is used to bring in air from the engine turbines and then cool and pressurize it to make it breathable. However, in the event of an emergency, the plane is already equipped with oxygen systems which can be accessed by passengers and cabin crew members through masks. On most aircraft, there are actually two separate oxygen systems with one for the crew and the other for the passengers. Typically, if the cabin pressure drops to below a certain level, the emergency system is triggered, dropping oxygen masks that will provide air to passengers for 15 to 20 minutes, and for the crew members for around 30 minutes. This is generally more than enough time for the aircraft to descend to a lower altitude and bring the cabin air pressure back to a safe, breathable level.
Oxygen equipment is a crucial safety feature on aircraft, but it does come with its own challenges. The first of these challenges is designing the instruments so that they fit the dimensions of the plane. Not all oxygen systems use canisters of gaseous oxygen—some have chemical oxygen generators that create breathable air by way of chemical reaction as needed. Depending on which option an aircraft uses, the oxygen equipment may require more or less regulated space. Another main challenge to consider is effectively securing the oxygen masks and tanks or generator so that there is no leakage or contamination. Aircraft regularly enter harsh environments which expose on board equipment to vibration and pressure changes that make securing sensitive parts a crucial element of aircraft construction. Finally, the oxygen equipment needs to be responsive to cabin pressure and altitude, and must be easy for passengers to use with minimal time needed to secure a mask.
Besides simply splitting the oxygen systems into one for the crew and another for passengers, there are a number of other regulations which inform how oxygen equipment systems are designed. Most importantly, the altitude at which an aircraft flies will determine the level of preparation that is needed. In pressurized vessels that fly at altitudes where the atmospheric pressure is below 376 hPa, all crew members must have a quick-donning type of oxygen mask at their flight duty stations. These planes should also be equipped with automatically deployable oxygen equipment that has a total number of oxygen masks which exceeds the number of passengers and cabin crew seats by 10 percent. On non-pressurized aircraft, the requirement is less, but there should still be enough oxygen equipment for all crew members and 10 percent of the passengers whenever entering a higher altitude temporarily.
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