Posted by: Korry | November 29, 2011

Techie Tuesday: Oxygen Masks

If you’ve ever been on an airliner, you’ve probably heard the flight attendants brief you on how to use the oxygen mask. It generally goes something like this: put the mask on, tug on the hose, and then assist other passengers or children in putting on their mask. This procedure is very important in the event of a cabin depressurization…but before I can explain that, I need to explain how the air in the atmosphere interacts with our bodies.

Our bodies need Oxygen (obviously). On the ground, our bodies are used to the amount of oxygen that exists in the air; however, as we gain altitude, the concentration of oxygen decreases significantly. Without oxygen, our bodies start to shut down. A lack of oxygen in the body is known as hypoxia, and while at 10,000 feet your body will rarely if ever suffer from hypoxia, at 30,000 – 40,000 feet your body may only function for a matter of a few seconds.

In a “pressurized” airplane such as any modern airliner, there are systems designed to stuff extra air into the cabin to increase the concentration of oxygen. This means that while you may be flying at 35,000 feet, your body (and also the cabin of the aircraft) probably only think you’re at 7,000 or 8,000 feet. This is why you don’t need to wear oxygen masks for most flights.

In some extremely rare events, however, the cabin fails to pressurize properly, and if the decompression happens while at a high altitude, the cabin will go from the safe 7,000 feet to the unsafe 35,000 in a matter of seconds. The good news is that as long as you breathe the oxygen from the masks that drop, you will be just fine. The masks are set to automatically deploy as soon as the cabin altitude surpasses 14,000 feet or so.

So why do I need to pull the hose to start the flow of oxygen? The passenger oxygen systems on most (but not all) airliners often use an oxygen generator for each row of seats. When you pull the hose, it’s like pulling the pin on a fire extinguisher and allowing the oxygen to start flowing. If you don’t pull the hose, you won’t get the oxygen. Don’t be surprised if the air is a bit warm as the chemical reaction that the oxygen generator uses to create the oxygen also creates heat. That is totally normal.

So why do you need to put your mask on first? This has to do with the limited time of useful consciousness at altitude. With potentially only a few seconds of time available, you need to put your mask on first so that you don’t succumb to the effects of hypoxia. It’s a lot harder to help the person next to you if you’re basically passed out.

The passenger oxygen will last between 10-15 minutes. That will be enough time for the pilots to descend the plane to a safe altitude around 10,000 feet where you won’t need the supplemental oxygen anymore. The best part is that even if you didn’t use the mask correctly, as soon as the plane is at a safe altitude, you will be just fine. I should say that if you are on a flight that encounters smoke in the cabin, know that the passenger oxygen masks mix cabin air with the supplied oxygen. That means the mask will not prevent smoke inhalation, so put a rag or a shirt over your mouth if that’s the case.

If hypoxia is such a big issue for passengers then surely it must be a major concern for pilots, too, right? Absolutely! And there are lots of rules and regulations they must adhere to in order to ensure they don’t encounter hypoxia. Some of these rules require pilots to wear their [much more sophisticated] oxygen masks if one of the pilots leaves the cockpit, or if flying high enough, to wear a mask all the time just in case of a decompression.

While the chances of you ever needing to put on your oxygen mask are incredibly small, it’s always smart to be prepared. Listen to the flight attendant announcements and if you have any questions regarding how the systems operate, definitely ask a question.

Do you have a technical question about airplanes or airlines that you’ve always wondered about? If so, email me at and you may find your answer in an upcoming edition of Techie Tuesday.

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