How do you know if an oxygen mask is working?

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Old Jul 5, 19, 8:27 am
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How do you know if an oxygen mask is working?

Aside from not passing out, how does one know that the mask is working?

- Is there a visible flow indicator on the tubing? Does it change color or otherwise indicate O2?

- Do the masks make a noise as the generators produce oxygen?

- How long does it take between the time when masks drop down that there is adequate O2 generated?

- On some planes, like the 787, there is no instruction about how "the bag may not inflate." I thought that the bag served as a reservoir for oxygen (or--rather--air mixed with oxygen.) What happens if there is no reservoir bag?

- Is it okay to keep vaping? (Just kidding.)
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Old Jul 6, 19, 1:59 pm
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I do not believe there is any sort of flow indicator.

The generator is spitting out pure oxygen. The bag collects it during the time you're not inhaling.
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Old Jul 7, 19, 12:10 pm
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Why worry about it? It either works or doesn't. If the mask deploys put it on. Pulling down the mask actuates the generator.

Chemical oxygen generator
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Old Jul 8, 19, 9:50 am
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the bag is always source of annoyance for me - the wording should be "might not inflate." Also, critically important on most systems is ensuring the lanyard is pulled so that the unit is activated - it is a terrible shame that some passengers have been found dead in their seats with the masks on in an otherwise survivable incident because the unit was not activated (and sometimes because they took the mask off thinking it was not working because the bag did not inflate.

I think the pre-flight safety instructions do not do enough to emphasize these issues. (of course, many folks aren't even paying attention, but that's a different thread).
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Old Jul 8, 19, 9:53 am
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After extensive Googling, I found that there is a flow indicator, which turns green if oxygen is coming through the mask.

The unanswered questions are...

1. Why is there no reservoir bag on the 787?
I read that the masks fit differently on the 787; they "automatically adjust," hence no elastic strap. But that doesn't explain the absence of a reservoir bag.

2. How long does it take between pulling down on the tubing for the chemical reaction to generate adequate oxygen?
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Old Jul 8, 19, 12:24 pm
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Mats,

It really doesn't matter. You grab the one over you. If it works, you'll know it. If you start fading out, you know it's not and beat the crap out of the person next to you and steal theirs.
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Old Jul 8, 19, 2:22 pm
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For those who haven't had high altitude training the onset of hypoxia can be very quick in an explosive decompression event or somewhat longer in a slower decompression. As hypoxia sets in you really won't care that your mask isn't working.
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Old Jul 11, 19, 10:08 pm
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Originally Posted by catocony View Post
Mats,

It really doesn't matter. You grab the one over you. If it works, you'll know it. If you start fading out, you know it's not and beat the crap out of the person next to you and steal theirs.
Theirs is probably fed by the same generator yours is--if yours doesn't work then theirs most likely doesn't, either.
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Old Jul 12, 19, 12:18 am
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Typically it's one generator per seating block (e.g. in Y one for three +1 for infant) - Mentour has a YT video about that (and what's "up" for the crew+cockpit)
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Old Jul 12, 19, 10:43 am
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If you pass out - it ain't working.

If you sit there gasping for breath, feeling pain in your chest with each inhale and exhale, chanting, "I can't breathe! I can't breathe!" - it's working.
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Old Jul 14, 19, 9:22 am
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Originally Posted by WillCAD View Post
If you pass out - it ain't working.

If you sit there gasping for breath, feeling pain in your chest with each inhale and exhale, chanting, "I can't breathe! I can't breathe!" - it's working.
LOL it's funny because I can imagine myself creating this exact same drama.
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Old Jul 15, 19, 2:18 pm
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Originally Posted by Mats View Post

1. Why is there no reservoir bag on the 787?
https://www.asma.org/asma/media/AsMA...449_Garner.pdf

After the turn of the most recent century development of the Boeing 787 transport aircraft was characterized as advanced and visionary. As part of the many development programs designated for this aircraft, the passenger oxygen system was to leverage a high efficiency approach long known to be successful in clinical applications requiring oxygen supplementation (1) . Whereas the historical approach to the passenger system utilized a continuous flow of oxygen either from cylinders or generators, the new system was going to provide an altitude specific volume of oxygen triggered by inspiration.
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