Most passengers—especially frequent travelers—don’t pay much attention to the flight attendant safety briefings. That said, there is actually some good information being passed along, and as a potential professional pilot, it would be wise to start learning some of it yourself.

For instance, how much attention have you paid to the discussion about the oxygen masks falling from the ceiling? You might know that you need to put the mask on during a depressurization situation, but did you pay any attention to the particulars? If not, you should.

The oxygen that you will breathe during a depressurization actually isn’t on the airplane yet. It has to be produced, and guess who does that? You do.

Every jet uses some kind of a pressurization controller to maintain cabin altitude. If the cabin climbs above a certain setting (around 14,000 feet msl), the controller will (should) release the “rubber jungle” into the cabin. If the automatic system fails, the pilots can manually deploy the masks, but first they need feedback from the flight attendants that the masks didn’t fall. If there are a few units that don’t work, the flight attendants can use a tool to pop open the doors of the unit that is right over your seat.

Once the masks are out, there is a catch: Oxygen isn’t generated until you pull the mask toward you. You actually need to give it a little tug, because the hose is attached to a pin that needs to be tripped. When you give that mask a tug, the pin activates a chemical reaction that will then produce the oxygen that you will breathe. This is why you’re told that you should put on your mask first and make sure it’s activated. If the cabin depressurizes at a high altitude, there won’t be much time of useful consciousness, and if you can get your mask working, then you can help a child or someone next to you.

Once the canister is activated, it generates a tremendous amount of heat, so you don’t want to reach up and touch it. It can—and will likely—also produce a bit of a burning or foul odor. You don’t want to mistake that for a possible fire. It is instead a sign that the system is working as advertised. There may also be a bit of dust or smoke, both of which can generally be ignored.

What the flight attendants don’t tell you is this: The canisters only produce enough oxygen for around 12 minutes of breathing, though you may be able to get 15 minutes out of it. Worse, the oxygen is a continuous flow. It doesn’t matter how deeply or slowly you breathe. The good news with that is that if you (or a seatmate) pass out, air is available. The bad news is that if you pull down on two masks at once, you will still only have the 12 minutes of air to use. So, if you are in a row of three seats by yourself, you might have 36 to 45 minutes of air to use if you use them consecutively.

Why so little time? The assumption is that a depressurization at altitude is going to be followed by an immediate and rapid descent to (preferably) 10,000 feet. Since passenger jets are limited to 41,000 feet, the crew would be trying to lose 31,000 feet. In 12 minutes’ time, that works out to around 2,600 feet per minute, which should be very easy to do. Keep in mind that this is a worst-case scenario, because very few full jets can reach FL410.

So, next time you board, pay attention to the safety briefing. There are nuggets of information in there that really can save your life. And in this case, they will also be on a checkride if you are looking to fly professionally.—Chip Wright