The O2 masks in the main cabin are "rebreathers". The low flow of oxygen mixes with the cabin air or lack of cabin air. They are of no real value in a smoke situation.

This entire scenario depends on how high you are and what type of decompression. If the cabin depressurization is very slow, say 1000fpm, there is plenty of time for the pax to get their O2 masks on and start breathing.

If its an explosive style or very quick decompression and you are at a very high altitude say 40,000', then you very well only have a few second (maybe 3-10) of "useful consciousness" to figure out what to do and get those masks on as the air is forced out from you lungs uncontrollably. Most people aren't going to be able to do it. If you have an explosive style decompression, the crew likely has other problems on their hands besides the oxygen as well.

What matters is the pilots get their masks on, which are not rebreathers, and get the airplane lower in an emergency descent. The cockpit uses quick donning style masks capable of supplying 100% oxygen. The mask seals to the face. Depending on altitude, the mask will also deliver a forced continuous flow of air (as opposed to a demand flow). The oxygen in the cockpit is supplied by bottle.

Flight attendants also have at their disposal small oxygen bottles used for emergency, first aid, etc.. but are not able to get to them quickly in a cabin depressurization. They will have to rely on pax masks while attending to their duties in the aisle most likely. Most aircraft drop more masks than there are seats to accommodate lap children.

 

One serious problem with the passenger mask system, as mentioned by an earlier writer in this thread, is that you do have to pull down on the tubing, apparently to move a pin in the canister, to begin the reaction and to get oxygen flowing. Even though the flight attendants always say this, I did not understand the importance of this maneuver until I looked at the system. I think that most passengers would assume that the oxygen is from a tank where this action would be unimportant. A recent NPR quiz show asked panelists about the common things done on a commercial airplane, and when asked about oxygen masks, the "Pull on the tubing to initiate the flow of oxygen" was not mentioned. I would think that the flight attendants should be instructed to say that "Oxygen will not begin to flow until you pull firmly on the tubing" rather than using their current script.

 

Try and do some research. You should go on YouTube and type in safety demonstration. I'm sure you'll find that you're wrong with that statement. Most airlines say pull down on the mask and then pull it towards you.

 

2:33 into the video

https://www.youtube.com/watch?v=kfFHn6DxvEg

 

Ah, so you are referring to passengers who are talking, texting, sleeping, or anything else instead of listening to the FA safety demo where they are instructed to pull down on the cord towards them.

Sounds like Darwin solved this issue for you 150 years ago.

 

Hey Doc,
A more serious question to ask is why do the lavs drop 2 masks.

 

For the lady who actually uses the changing table in there vs. using the seat back tray...

nothin better than snack peanuts and a side O'poo smear.

 

Some people are thoughtful enough to leave an overloaded dirty diaper in the map pocket as knee cushion.

 

Training materials for the citation excel (yellow plastic cups in the back) say they are ineffective until the cabin altitude is below 25,000

 

I heard that climax for men is better when they're close to asphyxiating.