The airlines care about our safety, etc…So they have emergency oxygen masks ready right over our heads. Fine by me.
But what’s that little bag for?
We’ve all heard it a million times, always in identical wording: “place the mask over your nose and breathe normally. Although the plastic bag may not inflate, oxygen is flowing”
So what’s with the bag thing? Is it supposed to inflate, or not? Why? And since it apparently has a mind of its own-("it may, or may not "), how does it make the decision to inflate?
The bag is really just an accumulator, a buffer so to speak. Oxygen is generated at a constant rate but your breathing is cyclic. The bag can’t inflate if you are sucking down the contents as fast as it’s being filled.
If they work like the oxygen machines at work, the bag is basically just a reservoir of oxygen. The oxygen flows at the same rate no matter what, and if you have an open system (not hooked up to a patient, or with leaks) it all runs out the tubing/mask/whatever. If you close the system (attach it to a patient without any leaks), some of the oxygen backs up into the bag. The fact that the bag isn’t inflating doesn’t mean there’s no air running, it just means you don’t have a complete seal. Given the varying sizes and shapes of people’s faces and people’s reluctance to really mash down on the mask, it stands to reason that some (or most) of them wouldn’t get good seals and thus their bags wouldn’t inflate. Even without the complete seal, you should still be getting enough supplemental oxygen to keep you in good shape.
They just don’t want people freaking out, thinking their neighbor is getting oxygen and they aren’t, and pandemonium breaking out.