B787 O2 supply

[Longtimer]

Boeing whistleblower raises doubts over 787 oxygen system

By Theo Leggett Business correspondent, BBC Newscopyright BoeingA Boeing whistleblower has claimed that passengers flying on board the company's 787 Dreamliner could be left without life-saving oxygen if the cabin were to suffer a sudden decompression.

John Barnett, a former quality control engineer at the company, says he organised tests which suggested that up to a quarter of the oxygen systems used on the aircraft could be faulty and might not operate when needed.


https://www.bbc.com/news/business-50293927

[OldnGrounded]

Boeing whistleblower raises doubts over 787 oxygen system

By Theo Leggett Business correspondent, BBC Newscopyright BoeingA Boeing whistleblower has claimed that passengers flying on board the company's 787 Dreamliner could be left without life-saving oxygen if the cabin were to suffer a sudden decompression.

John Barnett, a former quality control engineer at the company, says he organised tests which suggested that up to a quarter of the oxygen systems used on the aircraft could be faulty and might not operate when needed.


https://www.bbc.com/news/business-50293927

The story repeatedly refers to "oxygen bottles" for the pax O2 systems. Does the 787 not have O2 generators for the pax system? Or is the reference just the result of confusion on the part of the reporter and editors?

[Flight Alloy]

Nope, 787 uses O2 bottles both for flight deck and cabin oxygen systems. Each 3 seat group shares one oxygen bottle in the bulkhead overhead, fired by a pyrotechnic valve when operated. These valves, by definition single use, can not be tested, and are the source of failures.

[marchino61]

Nope, 787 uses O2 bottles both for flight deck and cabin oxygen systems. Each 3 seat group shares one oxygen bottle in the bulkhead overhead, fired by a pyrotechnic valve when operated. These valves, by definition single use, can not be tested, and are the source of failures.
Presumably a number of bottles from each batch are destructively tested to confirm - at least statistically - that they work?

[physicus]

Indeed they were, as per the article, and 25% were shown to fail. A problem which the whistleblower reported to the FAA after Boeing didn't do anything about it. And neither did the FAA. The plot thickens.

[ATC Watcher]

787 uses O2 bottles both (....) , fired by a pyrotechnic valve when operated. These valves,(...) are the source of failures.
A very good combination of words in one sentence. A prone to failure pyrotechnic device to open a bottle of Oxygen in an aircraft ?
Is this for real ?

[double_barrel]

Nope, 787 uses O2 bottles both for flight deck and cabin oxygen systems. Each 3 seat group shares one oxygen bottle in the bulkhead overhead, fired by a pyrotechnic valve when operated. These valves, by definition single use, can not be tested, and are the source of failures.

O2 bottles triggered by faulty pyrotechnic devices. What could possibly go wrong?

[AndoniP]

O2 bottles triggered by faulty pyrotechnic devices. What could possibly go wrong?

the valves are triggered by pyrotechnics. not the bottles.

[kiwibrit]

It's decades since worked with an airliner - VC10 in the RAF. But IIRC a functional check of all the passenger oxygen masks was an item of a periodic maintenance schedule. I assume that I still so with modern airliners? In which case, I would expect the airlines to be concerned at a high incidence of failure (25%) and to raise the issue with Boeing and the CAA / FAA. So it would not have needed a whistleblower to raise concern effectively. I can't see that the story adds up. That said, I accept that I am a long time away from the aircraft maintenance scene.

[physicus]

The pyrotechnically activated O2 bottles would have a certified lifetime beyond which they need replaced, but they evidently wouldn't be tested in the mean time as they are single use by design. There are several far more dangerous pyrotechnic agents on board passenger aircraft - none of those ever caused a problem to my knowledge - such as flares in the survival kit, and some escape slides/rafts have chemical agents to inflate them. I wouldn't get too excited about the activation mode of the bottles. But the failure rate and subsequent cover up by Boeing management AND the regulator, well, that is an entirely different story!

[Flight Alloy]

It's decades since worked with an airliner - VC10 in the RAF. But IIRC a functional check of all the passenger oxygen masks was an item of a periodic maintenance schedule. I assume that I still so with modern airliners? In which case, I would expect the airlines to be concerned at a high incidence of failure (25%) and to raise the issue with Boeing and the CAA / FAA. So it would not have needed a whistleblower to raise concern effectively. I can't see that the story adds up. That said, I accept that I am a long time away from the aircraft maintenance scene.
No system based on single use chemical oxygen generators or pyrotechnic valves will undergo a 'functional check', meaning an actual check of delivering oxygen in an emergency situation. By functional check they mean the mask is still in one piece, not dried out, the bulkhead hinge opens, and the hoses haven't fallen off. This does not constitute a 'functional check', if so, every test would require a full replacement of the whole SINGLE USE emergency oxygen system, certainly a multi million dollar cost item. That is the reason they are NEVER tested. Also, how often do airlines suffer depressurization with extended high altitude flight, where some failed masks would result in detectable injury to passengers? Luckily very rarely, as most incidents result in immediate expeditious descent to breathable atmosphere, where in such an event a lack of functioning mask would almost be undetectable and its use practically unnecessary, but there are regimes of flight where an emergency descent would be impossible for extended periods, like most of the Chinese highlands. And you're still surprised Boeing would under-report a major safety issue, after MCAS, 777X doors, pickle forks, trim wheel etc etc. ad nauseum? Really get ahold of yourself.

[OldnGrounded]

Nope, 787 uses O2 bottles both for flight deck and cabin oxygen systems. Each 3 seat group shares one oxygen bottle in the bulkhead overhead, fired by a pyrotechnic valve when operated. These valves, by definition single use, can not be tested, and are the source of failures.

Thanks for the information.

[Radgirl]

Also, how often do airlines suffer depressurization with extended high altitude flight, where some failed masks would result in detectable injury to passengers? Luckily very rarely, as most incidents result in immediate expeditious descent to breathable atmosphere, where in such an event a lack of functioning mask would almost be undetectable and its use practically unnecessary

Why bother to have slides? Or any other emergency equipment for 'rare events'? Would you care to tell us the duration of consciousness in the case of sudden depressurisation in the cruise for a healthy adult? And would you care to postulate on how long an elderly patient with heart disease would survive? And compare it with the time needed for an emergency descent to 10,000 feet?

Not sure I would be happy without oxygen. Must pick one of the 75% of seats that has working oxygen. Ryannair would probably be charging a premium for them if they operated them

[OldnGrounded]

Why bother to have slides? Or any other emergency equipment for 'rare events'? Would you care to tell us the duration of consciousness in the case of sudden depressurisation in the cruise for a healthy adult? And would you care to postulate on how long an elderly patient with heart disease would survive? And compare it with the time needed for an emergency descent to 10,000 feet?

Not sure I would be happy without oxygen. Must pick one of the 75% of seats that has working oxygen. Ryannair would probably be charging a premium for them if they operated them

Time of useful consciousness at FL400: 15-20 seconds. Probably less than that for me, with significant heart disease in my old age.

Emergency descent from FL400 to 10,000 ft: A lot longer.

Flight Alloy:
Also, how often do airlines suffer depressurization with extended high altitude flight, where some failed masks would result in detectable injury to passengers?

Probably good to note that the "detectable injuries" to pax with non-functioning masks would likely range from significant permanent brain damage to death. Always important to consider when establishing risk factors.

[ATC Watcher]

Time of useful consciousness at FL400: 15-20 seconds. Probably less than that for me, with significant heart disease in my old age.
Emergency descent from FL400 to 10,000 ft: A lot longer.
Probably good to note that the "detectable injuries" to pax with non-functioning masks would likely range from significant permanent brain damage to death. Always important to consider when establishing risk factors.
Not a medic but I think the critical part is from 400 to 300 , at 4000 ft/min (typical emergency descent on most types) say 2- 3 min deprivation ; like a long underwater scuba dive ., brain damage ?
But from 30.000ft you get back a bit of oxygen , there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
But again I am not a brain specialist..
I just remember a decompression on a Spantax DC8 over the Netherlands from FL33 or 370 where half the O2 masks did bot deploy because stuck by nicotine tar .. Diverted to AMS. .. Nobody was injured, shocked yes, but most of the pax continued a few hours later to the Canaries...

[OldnGrounded]

Not a medic but I think the critical part is from 400 to 300 , at 4000 ft/min (typical emergency descent on most types) say 2- 3 min deprivation ; like a long underwater scuba dive ., brain damage ?
But from 30.000ft you get back a bit of oxygen , there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
But again I am not a brain specialist..
I just remember a decompression on a Spantax DC8 over the Netherlands from FL33 or 370 where half the O2 masks did bot deploy because stuck by nicotine tar .. Diverted to AMS. .. Nobody was injured, shocked yes, but most of the pax continued a few hours later to the Canaries...

Humans are variable creatures, of course, but three minutes is the generally-accepted period after which hypoxic/anoxic brain damage is of serious concern. The FAA tables show TUC at FL300, with rapid decompression, as 30-60 seconds:

https://www.faa.gov/pilots/training/airman_education/media/AC%2061-107A.pdf

Of course, that doesn't mean brain damage at that limit, but it does mean that few will be able to don those masks if they don't do so very quickly.

I don't mean to suggest that serious or permanent injury is guaranteed, just that it's far too serious a risk to discount. You really, really want all the pax O2 systems to work when the cabin undergoes rapid decompression.

[kiwibrit]

Thanks for the tech briefing, including why the O2 supply is not tested, Flight Alloy. I think that the RAF VC10 C Mk1s I worked with in the late 60s had a manifold supply to the passenger emergency masks. Thereafter my aircraft experience was with military non passenger aircraft. I shall now retire back into my cave!

[Lake1952]

I would prefer that my cockpit crew test their oxygen supply to assure it works.

[Flight Alloy]

Why bother to have slides? Or any other emergency equipment for 'rare events'? Would you care to tell us the duration of consciousness in the case of sudden depressurisation in the cruise for a healthy adult? And would you care to postulate on how long an elderly patient with heart disease would survive? And compare it with the time needed for an emergency descent to 10,000 feet?

Not sure I would be happy without oxygen. Must pick one of the 75% of seats that has working oxygen. Ryannair would probably be charging a premium for them if they operated them
Oh I think you misunderstood my intention with that statement. I just wanted to illustrate why deleterious effects from non functioning O2 masks seam quite rare, and why airlines aren't 'up in arms' because of possible faulty equipment, because (luckily) flight regimes where masks save lives are quite rare, but still occur (any time you're flying over mountains basically). I certainly advocate for plenty of emergency equipment, I was just highlighting why we might not have seen many injuries related to these failures, specifically because most depressurizations occur in regimes where quick emergency descent is possible, so even not using a mask should not cause serious injury. Unfortunately it is almost always media pressure and 'learning from mistakes' that drive (aviation) improvements, and not an inherent drive for safety from the airlines, so presumably they would only insist on improvements if incidents were to occur with more frequency.

[Flight Alloy]

Here is a link to the original STORY (https://www.thelastboeinginspector.com/the-last-inspectors-blog/brave-boeing-qa-manager-whistleblower-comes-forward-corroborating-rampant-boeing-qa-management-fraud-endangering-your-safety-and-exposes-that-in-a-787-emergency-only-75-may-be-able-to-get-emergency-oxygen) written by Gerald Eastman on his blog 'The Last Inspector' more than 1,5 years ago. The guy was a quality inspector for Boeing for many years and chronicles his battle for transparency and safety against the corporate machine of rushing jobs for profit. His blog is full of stories of his own and other colleagues experiences at both Boeing factories about corners cut, non conforming parts liberated from scrap cages and installed into production airframes to maintain production, and the pressures of management to bury any safety concerns and maintain tempo. He also goes into the complacency for the FAA in responding to whistleblower complaints and how the system worked to punish anyone with an ounce of integrity. Do head over and read if interested in the internal goings on by someone experienced in the business! Here's the main blog too for reference: The Last Inspector (https://www.thelastboeinginspector.com/)

[OldnGrounded]

Here is a link to the original STORY (https://www.thelastboeinginspector.com/the-last-inspectors-blog/brave-boeing-qa-manager-whistleblower-comes-forward-corroborating-rampant-boeing-qa-management-fraud-endangering-your-safety-and-exposes-that-in-a-787-emergency-only-75-may-be-able-to-get-emergency-oxygen) . . .

Thanks for the link!

[topgas]

I thought there were more drop down passenger masks than seats, to allow for infants sitting on laps

[Speed of Sound]

there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.


These people are not walking along at sea-level (or whatever the cabin altitude is at the time of the depressurisation) one second, and the next they are at 39,000 feet. They spend many weeks and sometimes months acclimatising, where the number of red cells in their blood gradually increases to a level where the amount of oxygen scavenged from the atmosphere is greatly increased.

Even then, survival at that altitude is only for a matter of hours even with supplementary oxygen, which is why it’s called the ‘death zone’

[Easy Street]

there are lots of people that climb the Himalayas without oxygen

I was interested in the definition of ‘lots’ being used here so I turned to Google and found this (https://www.adventuresportsnetwork.com/outdoor/climbing-everest-adrian-ballinger-without-oxygen/) which quotes the all-time number of Everest summits without oxygen as 200 of the 5000 total ascents. So, an elite within an elite, who don’t just acclimatise for months: they train for years to reach that level of fitness, and probably self-select for some kind of genetic advantage too. Less than a planeload *ever* out of the thousands of planeloads that fly *daily*. Interesting use of ‘lots’ indeed! Even widening the net to include all those who climb from base camp to the oxygen-donning altitude, the numbers involved are still a drop in the ocean on the global statistical scale of the airline industry.

[Radgirl]

My previous post was done tongue in cheek. I do know what happens with a sudden decompression and the max ROD. A significant proportion of paxs would die. Others would have long term hypoxic effects - dont worry about the medicine, just be assured any good lawyer would be after $$$ £££s for loss of job attainment, failure of relationships, mood swings and potential early cognitive degeneration

Luckily I normally fly below 2000 feet so I am not effected but I am surprised at the laisse faire attitude to yet another Boeing issue. The fact that nobody has come to harm is a matter of luck not judgement. Surely this should be an issue to be sorted immediately with interim measures such as free standing oxygen??? If it had been cc oxygen......

[FlightlessParrot]

I thought there were more drop down passenger masks than seats, to allow for infants sitting on laps

I was going to ask about this. Presumably there is some over-provision to allow for failures: does it get near to 25% (assuming that figure for failures is true/typical)? I'd also like to ask if this is a Boeing problem, or more widespread (assuming this equipment is supplied by a third party).

[hans brinker]

I was going to ask about this. Presumably there is some over-provision to allow for failures: does it get near to 25% (assuming that figure for failures is true/typical)? I'd also like to ask if this is a Boeing problem, or more widespread (assuming this equipment is supplied by a third party).

The FAA, being data-driven, came to the same conclusion: there is four masks per row of three, plus a couple extra in the toilet, so if 25% don't work everyone should still have a working mask, statistically speaking. Really don't see what the problem you people have.





Oh, the whole row wouldn't work if the valve doesn't open....

[Busbuoy]

I would prefer that my cockpit crew test their oxygen supply to assure it works.
At my airline a functional check of all cockpit masks is required on the first flight of the crew day (i.e. not repeated at each turnaround). While the check is conducted "in container" i.e. the mask is not actually removed and donned, I have full confidence in the check other than it confirming that the gas being delivered is actually O2. I have to rely on ground servicing integrity for that.
To answer another poster's query, an additional pax mask is installed above every set of seats.

Regarding failure to use supplemental O2 in the case of depressurisation I'm going to go out on a limb and say that during even the worst case scenario, i.e. explosive depress at FL450 followed by a poorly flown emergency descent to an intermediate altitude due terrain followed by a further descent to 10000' within 30 minutes of initial depress, the risk of serious or lasting effects is very low except, perhaps, for physical injury due to unrestrained pax movements while unconscious, or rarer cases where an underlying medical condition is triggered by the resulting hypoxia.

My rationale:
While Time of Useful Consciousness at FL450 is quoted as 9-15 seconds (it may be less in affected people, think seriously unfit or heavy smokers) and is reduced by activity, think walking back to your seat, the time to actual unconsciousness is much longer. And the time to actual deleterious effects of hypoxia on brain or other cells is even longer still.
There are reports of passengers failing to refusing to don masks with no long-term or serious after-effects provided that the cabin altitude was reduced in the previously mentioned timely manner.

Now, I am not defending the position challenged by the OP. Safety-sensitive systems such as supplemental O2 systems should not be experiencing 25% failure rates and manufacturers and regulators should not be brushing aside genuine reports of such failures. O2 systems are installed for very good reasons but I get the feeling we are overstating the risk a little.

Ok, let the howling begin....

[EEngr]

Nope, 787 uses O2 bottles both for flight deck and cabin oxygen systems. Each 3 seat group shares one oxygen bottle in the bulkhead overhead, fired by a pyrotechnic valve when operated. These valves, by definition single use, can not be tested, and are the source of failures.

I wonder what the failure mode of the valve is. Open circuit in the squib (electric match)? Bad or weak pyrotechnic charge?

The squib circuit should be testable for continuity non-destructively. It's what demolition pyrotechnicians do prior to setting off a group of charges to bring a building down. The failure of some could result in the structure falling in an uncontrolled manner. I would be seriously surprised if the O2 system did not incorporate such a built-in-test (BITE).

Pyrotechnics themselves are pretty reliable, assuming that they are built with some quality control in mind. And if a suitable level of reliability can't be achieved, either redundant charges or a manual backup to open the O2 valve might be needed.

[ATC Watcher]

@ Speed of sound + @ easy Street : They spend many weeks and sometimes months acclimatising, where the number of red cells in their blood gradually increases to a level where the amount of oxygen scavenged from the atmosphere is greatly increased.
Good point . Agree . My point was about permanent brain damage and even death for being subject to single minutes of O2 deprivation. But you are right . Point taken.

[Fursty Ferret]

While Time of Useful Consciousness at FL450 is quoted as 9-15 seconds

In the event of a sudden decompression it’s closer to 5 seconds. You can’t hold your breath and your lungs will work in the opposite sense and dump oxygen from your blood to atmosphere.

If you can get to a breathable altitude within 90 seconds you’re probably going to be OK. The problem is that if someone has stopped breathing or suffered cardiac arrest from hypoxia, then they’re unlikely to spontaneously recover going below 20,000ft.

[2bigmellons]

I find this demonstration of a decompression at FL450 interesting and alarming.

Count how long it takes the prepared gentleman to lose consciousness.

https://youtu.be/6Efvl6AwILo

[Ian W]

I find this demonstration of a decompression at FL450 interesting and alarming.

Count how long it takes the prepared gentleman to lose consciousness.
SNIP VIDEO

At height say above 35,000 ft as the emergency oxygen masks are not pressurized they will not prevent loss of consciousness. However, the availability of higher percentage oxygen in the low pressure air being breathed means that the pax wearing masks will come round faster when back to 10,000ft and have less chance of brain damage. This is why an emergency descent to 10,000ft is required. Do not expect anyone in the cabin to be reliably responsive above that altitude.

[deltahotel]

Any idea why Boeing have gone for O2 cylinders rather than chemical generators? Space/weight/maintenance/cost?

[Meester proach]

Not a medic but I think the critical part is from 400 to 300 , at 4000 ft/min (typical emergency descent on most types) say 2- 3 min deprivation ; like a long underwater scuba dive ., brain damage ?
But from 30.000ft you get back a bit of oxygen , there are lots of people that climb the Himalayas without oxygen and they do not suffer brain damage.
But again I am not a brain specialist..
I just remember a decompression on a Spantax DC8 over the Netherlands from FL33 or 370 where half the O2 masks did bot deploy because stuck by nicotine tar .. Diverted to AMS. .. Nobody was injured, shocked yes, but most of the pax continued a few hours later to the Canaries...


4000’ per minute ? You ain’t even trying . 7500’ is achievable

[TURIN]

Any idea why Boeing have gone for O2 cylinders rather than chemical generators? Space/weight/maintenance/cost?
For the 787 the answer is invariably, "to save weight". However, there are other considerations such as the difficulty in transporting O2 generators after the Valuejet tragedy.

Regarding BITE checks, from memory I think there's an LED indicator on each bottle/valve assembly that shows the go/nogo state of the unit. I think they are ' on demand' too which means less O2 is required and therefore a smaller bottle, which again saves weight.

[fab777]

4000’ per minute ? You ain’t even trying . 7500’ is achievable

At VMO, gear extended and in a side slip, maybe. So definitely not realistic in the real life. 4000 is a correct figure.

[Maoraigh1]

"At height say above 35,000 ft as the emergency oxygen masks are not pressurized they will not prevent loss of consciousness."
How are the flightdeck masks pressurised? ( Not a professional, but thinking that "pressurised" does not, in this sense, refer to oxygen pressure at the mask.)

[deltahotel]

Flight deck masks can give air mix or 100% and they can also give over pressure - main use for smoke/fumes so the smoke can’t get into the mask but will also give an element of pressure to assist O2 uptake. Flight deck would be ok for a good length of time purely from an O2 perspective.

Pax masks don’t really seal so it’s only ever going to be O2/airmix at lowish pressure.

At 35000’ it’s minus lots - prob -50. Any time spent above 25000 gives a good chance of decompression sickness (sub aqua experts anyone? Bends chokes creeps staggers).

All the the above says get lower quickly. The 757 (Mr Boeing’s original streamlined crowbar) will do 6000fpm at Vmo, but if it’s a rapid decompress with the probability of structural damage do you really want to descend at Vmo?

Just some thoughts. Slightly easier as a freight pilot as everyone on board will be on the flight deck with proper masks and O2. Much harder with pax from 0 to very old, all of unknown health and no knowledge or training.

[Flight Alloy]

Flight deck masks can give air mix or 100% and they can also give over pressure - main use for smoke/fumes so the smoke can’t get into the mask but will also give an element of pressure to assist O2 uptake. Flight deck would be ok for a good length of time purely from an O2 perspective.

Pax masks don’t really seal so it’s only ever going to be O2/airmix at lowish pressure.

At 35000’ it’s minus lots - prob -50. Any time spent above 25000 gives a good chance of decompression sickness (sub aqua experts anyone? Bends chokes creeps staggers).

All the the above says get lower quickly. The 757 (Mr Boeing’s original streamlined crowbar) will do 6000fpm at Vmo, but if it’s a rapid decompress with the probability of structural damage do you really want to descend at Vmo?

Just some thoughts. Slightly easier as a freight pilot as everyone on board will be on the flight deck with proper masks and O2. Much harder with pax from 0 to very old, all of unknown health and no knowledge or training.




No mask can work as a 'pressurized' mask, aka delivering more pressure to the lungs than ambient, as without a pressure suit, the lungs and their muscles have very little capacity to breathe/pump air, as they fight to deflate the lungs with every breath against the oncoming pressure (imagine a balloon and trying to deflate it against pumping). With this limited muscle 'overcapacity', pressurized breathing is only possible with suits that also pressurize the chest area to the same pressure as the breathed gas.

[The Bartender]

No mask can work as a 'pressurized' mask, aka delivering more pressure to the lungs than ambient...

Right....
Google CPAP...

[wiggy]

No mask can work as a 'pressurized' mask, aka delivering more pressure to the lungs than ambient, ..... pressurized breathing is only possible with suits that also pressurize the chest area to the same pressure as the breathed gas

TBH I'm struggling to reconcile that statement with the practical training in pressure breathing that I and I'm sure some others here with an ex-military flying background will have experienced in the past.

It certainly is an interesting sensation, but as long as the differential isn't too excessive a pressure suit is not required, certainly not if you are going to only be pressure breathing for a short period of time.....

[deltahotel]

Thanks Wiggy.

Flight Alloy - have you experienced decompressions and pressure breathing in a chamber?

[Capn Bloggs]

Flight Alloy, what are you on about. You have obviously never worn a flight crew mask with Emergency set on the dial. PPrune...

[Peter H]

Flight Alloy: It is true that limited pressure breathing is possible, but this is limited to just the slight muscular 'overcapacity' the diaphragm muscles are capable of, in the range of fractions of an atmosphere.

Capn Bloggs: Flight Alloy, what are you on about. You have obviously never worn a flight crew mask with Emergency set on the dial.
Trying to get a ball-park figure I found a 2003 Lancet article on the "Physiological hazards of flight at high altitude"
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(03)15059-3/fulltext
"Which mentioned "positive pressure breathing oxygen masks that deliver up to 70 mm Hg", that's just under 10% of an atmosphere (760mm Hg).

Any idea what pressure modern flight crew masks actually deliver?

[Retired DC9 driver]

At VMO, gear extended and in a side slip, maybe. So definitely not realistic in the real life. 4000 is a correct figure.
I've demonstrated a 6500 FPM descent in a light A-319. You need to disconnect the autopilot, hand fly to get more flight spoiler extension. But it went down in a hurry. LA Centre had asked us to "expedite descent". My F/O looked a little concerned..
But I realize this thread is about the 787. I only flew the 767 plus the Airbus.

[Capn Bloggs]

Any idea what pressure modern flight crew masks actually deliver?
Not numerically. I do know that when our masks are on Emergency, there is significant overpressure, to the point where it is difficult to talk normally. The Emerg setting is for smoke/fumes use, not for a "normal" depressurisation.

[hans brinker]

I've demonstrated a 6500 FPM descent in a light A-319. You need to disconnect the autopilot, hand fly to get more flight spoiler extension. But it went down in a hurry. LA Centre had asked us to "expedite descent". My F/O looked a little concerned..
But I realize this thread is about the 787. I only flew the 767 plus the Airbus.
The A319 (or A321) doesn't have any extra spoilers with AP OFF, only A320. Maybe your FO was concerned you didn't know that.

[Flight Alloy]

Flight Alloy: It is true that limited pressure breathing is possible, but this is limited to just the slight muscular 'overcapacity' the diaphragm muscles are capable of, in the range of fractions of an atmosphere.

Capn Bloggs: Flight Alloy, what are you on about. You have obviously never worn a flight crew mask with Emergency set on the dial.
Trying to get a ball-park figure I found a 2003 Lancet article on the "Physiological hazards of flight at high altitude"
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(03)15059-3/fulltext
"Which mentioned "positive pressure breathing oxygen masks that deliver up to 70 mm Hg", that's just under 10% of an atmosphere (760mm Hg).

Any idea what pressure modern flight crew masks actually deliver?
Peter, thanks for putting some numbers to our claims, it makes determining fact from fiction objective as it should be. Some documentation I found, Hypoxia an Invisible 'Enemy Cabin depressurization effects on human physiology' (https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/hypoxia-an-invisible-enemy.pdf) from 2006, states this:
Another additional means for hypoxia protection is positive pressure breathing, which is usually found in modern crew oxygen masks and means the delivery of pure oxygen under pressure into the respiratory tract. For civil applications positive pressure breathing is able to increase additionally the oxygen partial pressure by around 20 to 30mbar provided that the overpressure condition is limited to some minutes only.
At sea level, oxygen has a partial pressure of about 200 mbar, at 40,000 ft, ambient pressure is reduced to around 180mbar, so with 100% O2 setting providing 180mbar of oxygen and a further 30 mbar of pressure breathing, one is back up to 210mbar of breathing oxygen, about the sea as at sea level. In this configuration, the pressure breathing element only provides 14% of the total oxygen delivered.
As one can plainly see, the overpressure provided is minimal, compared to sea level, the overpressure is 3% of atmospheric, at altitude, it constitutes only 15% over ambient.
So as I had stated before, yes, limited pressure breathing is possible, but it only constitutes an overpressure of 3% of an MSL atmosphere, aka a very minimal overpressure fraction, again due to the fact that our lung muscles have very limited overcapacity to process that pressure and not suffer any rupture injuries. I am sure it may 'feel' significant to the pilots who have experienced it, but numbers show that the overpressure component is a minimal, almost negligible component of the breathing system at altitude in all aircraft without the provision of pressure suits.

[Flight Alloy]

Right....
Google CPAP...
Thanks for the tip.The medical journal Thorax,
J H Ficker, G H Wiest, G Lehnert, B Wiest, E G Hahn, Evaluation of an auto-CPAP device for treatment of obstructive sleep apnoea. Thorax 1988;53:643–648. (https://thorax.bmj.com/content/thoraxjnl/53/8/643.full.pdf)
gives a CPAP average treatment pressure of 7.8mbar above atmospheric, which comes out to around 0.8% above ambient pressure. I wouldn't exactly call that 'overpressure breathing', a stiff wind should cause higher pressure differential. Before doing the whole LMGTFY game, perhaps you would consider informing yourself a little bit too before spouting unfounded statements?

[Radgirl]

Gentlemen, I regret you are mixing many different issues and talking physiological nonsense. CPAP has nothing to do with oxyenation in OSA but may improve arterial oxygenation in the abnormal lung. Positive pressures cant simply be added to partial pressures and the phrase lung muscles have very limited overcapacity to process that pressure is just a mismash of words.

Bottom line is that sudden depressurisation at 35 to 40,000 feet will kill at least some without oxygen regardless of how fast you can expedite descent. A non venturi non pressurised mask providing 100% oxygen will prevent cerebral apoptosis. A pressurised mask will prevent fumes being inhaled and a demand valve pressurised system can allow normal function

I remain staggered that everyone isnt up in arms that passengers are in effect being put at risk in a seat lottery over a safety provision that has been mandatory for decades

I will now withdraw to prevent my repetition

[MechEngr]

Not numerically. I do know that when our masks are on Emergency, there is significant overpressure, to the point where it is difficult to talk normally. The Emerg setting is for smoke/fumes use, not for a "normal" depressurisation.

Looking at 14.5 psi at 0 vs 3-5 psia at altitude. To make a significant amount of change is 3-8 psia. A mask will cover a triangle 6 inches tall and 6 inches wide. The area of that is 18 square inches, so you would need between 54 pounds and 144 pounds of strap tension to hold the mask on the person's face; not including the preload to keep from leaking out past the rubbery flesh of the face.

I expect the pressure delivered is on the order of .1 to .4 psig, which is a slight positive pressure that works because the actual need is to provide a partial pressure of oxygen equivalent to 10,000 ft and the 3-5 psi at altitude on pure oxygen accomplishes that; there's also a need to exclude smoke/toxic gases. Yes, even that low gauge pressure makes it tough to talk. Considering that lungs have a section area close to 100 square inches, even a 0.1 psi load is like having a 10 pound weight on your chest to resist.

From the scuba people:

"The important number isn't the total pressure in the lung but rather the difference in perssure between inside the lung and outside the lung. If the pressure in the lung is 95-110 cm H2O higher than the pressure outside the lung, the lung can rupture.

(100cmH2O= 0.097ATA= 0.098bar= 1.42PSI= 73.55mmHg approx.)"
Search scubaboard with the above text for more, sometimes grisly, details. Mind that this is the rupture pressure; it will be very uncomfortable before reaching this level.

[safelife]

Cabin O2 masks are certified up to 25.000 ft.

[DaveReidUK]

Bottom line is that sudden depressurisation at 35 to 40,000 feet will kill at least some without oxygen regardless of how fast you can expedite descent.

By "sudden", do you mean near-instantaneous ?

That would imply some kind of catastrophic structural failure where lack of oxygen might well be the least of your problems.

In a more likely scenario, does anyone have ballpark figures for the likely cabin pressure decay vs time resulting from, say, a window blowout, assuming that all the packs are still running and (by then) the outflow valve has closed ?

[wiggy]

MechEngr

..so you would need between 54 pounds and 144 pounds of strap tension to hold the mask on the person's face; not including the preload to keep from leaking out past the rubbery flesh of the face.

Just to try and tie up any remaining scepticism over pressure breathing and mask pressures from last night.. I've had time to check logbooks and we used to train under medical supervision for pressure breathing at 45K, using mil kit, individually fitted ( FWIW bone dome, attached mask with a rigid outer shell but no pressure jerkins or similar).

However that was then, this is now and these days I certainly wouldn't want to risk the same using a generic quick don one size "fits all" ( or doesn't :ooh:) Eros type mask as found in many flight decks..

Bottom line (for me) is that whilst you can protect yourself from a decompression quickly and reasonably adequately on the flight deck anybody in the cabin is very exposed, as Radgirl has pointed out..

[Beamr]

In a more likely scenario, does anyone have ballpark figures for the likely cabin pressure decay vs time resulting from, say, a window blowout, assuming that all the packs are still running and (by then) the outflow valve has closed ?

First of all, I do not have an answer to your question. But I'd say it is very dependant on the aircraft type and the damaged that occurs. Pressure decay is also dependant on the volume of the aircraft vs the size of the hole on it. Then you'll add the air conditioning, outflow valve position etc to the equation. I would imagine that situation gets very bad much quicker in a F16 than in an A380.

[QUOTE=Radgirl;10613667]
Ma´am, I am very hesitant to say that there would be fatalities due to hypoxia even when starting the emergency descent from high levels. If we stick to "high level", the National Airlines 27 encountered an uncontained engine failure at 39000ft with hull breach and one passenger sucked out. All but that one survived. With the Aloha 243 incident there isn't much to debate: the pressure was gone that instant (at 24000ft), yet all but one survived. With the Southwest 1380 the depressurization at 32000ft was described as "rapid", yet again all but one survived. The fatalities obviously weren't due to hypoxia.

In all these cases the cause of death was anything but hypoxia. I would say that there are far more serious consequences with hull breach than risk of hypoxia, if the plane is brought down below 10000ft as soon as possible.

[bucoops]

Thanks for the tip.The medical journal Thorax,

gives a CPAP average treatment pressure of 7.8mbar above atmospheric, which comes out to around 0.8% above ambient pressure. I wouldn't exactly call that 'overpressure breathing', a stiff wind should cause higher pressure differential. Before doing the whole LMGTFY game, perhaps you would consider informing yourself a little bit too before spouting unfounded statements?

My CPAP machine can supply at up to 20 cmH2O. Not sure how that translates but when I first started using it, it woke me in the middle of the night with the feeling of drowning in air. A very disconcerting feeling I can assure you. Obviously this was at normal atmospheric level, not FL45 or so.

[Fursty Ferret]

I've demonstrated a 6500 FPM descent in a light A-319. You need to disconnect the autopilot, hand fly to get more flight spoiler extension. But it went down in a hurry. LA Centre had asked us to "expedite descent". My F/O looked a little concerned..
But I realize this thread is about the 787. I only flew the 767 plus the Airbus.

The speed brakes on the 787 are phenomenally powerful, and using full speed brake coupled with a loss of cabin pressure triggers a further extension. I’ve seen upwards of 10,000fpm in the sim, and easily 4000fpm with the speed held back at about 250kts.

[Flight Alloy]

My CPAP machine can supply at up to 20 cmH2O. Not sure how that translates but when I first started using it, it woke me in the middle of the night with the feeling of drowning in air. A very disconcerting feeling I can assure you. Obviously this was at normal atmospheric level, not FL45 or so.
That comes out to about 19mbar, a fairly high setting from what I have read, but still only amounts to 2% over ambient pressure. Just goes to show how 'sensitive' ones lungs are and how accustomed we are to 'normal' breathing.

[physicus]

In the 744 sim both outflow valves open and with all packs running results in a 4000fpm cabin ROC. One outflow valve is about the size of four windows... I would infer from this that the packs can probably keep pressurisation at level with two or three busted windows, hence no explosive decompression would ensue from that. Peel off some skin or blow out a cargo door of course and that's a different story...

[Surlybonds]

our lung muscles have very limited overcapacity

I'd love for you to point out on an anatomical diagram where you think the lung muscles are... There ain't no such animal.

Chest muscles, and Diaphragm muscle, yep, but neither of those have a "capacity" as such, the chest cavity can expand by up to 1.5 to 2 litres from maximum exhalation to maximum inhalation.

[Surlybonds]

...Now at external pressure that is lower than internal lung pressure, which are being pressurized by, for sake of argument, a continuous air supply, our lungs are inflated like a balloon. This force could be multiples of the normal inspiration force that is normal. Our lungs have a limited expansion capacity before injury occurs, linings are torn, intricate alveoli and arteries ripped, they explode, baro-trauma?

Even in a decompressed aircraft, the pressure differential between the external environment and the internal lung pressure is not going to be anywhere near enough to cause damage. We are talking about low flow rate supplementary oxygen, maybe 10 litres/min, not connecting the patient to a high pressure air-line. Baro-trauma is usually the result of being too near the shockwave of an explosion, or other such high pressure events.

If you manually ventilate a patient in respiratory arrest - where the diaphragm and intercostal muscles are dormant - you can feel when you have met the elastic limit of the lungs, and any excess volume will be expelled round the seal of the mask. But even in a fully intubated patient using an automatic ventilator, you would be unlikely to cause any baro-trauma.

To try and drag this discussion back to some sort of relevance, the purpose of the passenger air masks is not to ventilate the patient, but simply to increase the partial pressure of oxygen within the mask, and therefore the lungs, to the point where anoxia does not occur.

[Flight Alloy]

Even in a decompressed aircraft, the pressure differential between the external environment and the internal lung pressure is not going to be anywhere near enough to cause damage. We are talking about low flow rate supplementary oxygen, maybe 10 litres/min, not connecting the patient to a high pressure air-line. Baro-trauma is usually the result of being too near the shockwave of an explosion, or other such high pressure events.

If you manually ventilate a patient in respiratory arrest - where the diaphragm and intercostal muscles are dormant - you can feel when you have met the elastic limit of the lungs, and any excess volume will be expelled round the seal of the mask. But even in a fully intubated patient using an automatic ventilator, you would be unlikely to cause any baro-trauma.

To try and drag this discussion back to some sort of relevance, the purpose of the passenger air masks is not to ventilate the patient, but simply to increase the partial pressure of oxygen within the mask, and therefore the lungs, to the point where anoxia does not occur.
Fully agreed in the case you specify here. That's why I specifically stated in my case a continuous flow over-pressure mask that would pressurize the lungs, as to illustrate the fact that both 'lung muscles' and the lungs themselves have a capacity limit that when reached results in bad things. I hope we can leave it there.

[ATC Watcher]

I find this medical discussion fascinating, and educative, but very theoretical.
In my 35 years as a radar controller controlling mostly upper airspace, I had to witness a few emergency descent myself, and saw a lot more on replay.
On the ROD : except from very old types like CV990 which could put 4 reverses in flight and could go down with 10.000 ft/min, the DC8 which could put the inboards in reverse and do 6000 ft/min , most of the others did around 4000 .I never seen a 787 doing one , left before they arrived.
After the incidents occurred , except from some minor injuries ,I cannot recall anyone killed or being permanently brain damaged. I have never read anything like this on incidents reports from rest of the world either. People sucked out if seated besides the hole.. yes, but Dead by hypoxia during a descent ? But maybe someone here can find references. .
And I mean hypoxia during an emergency descent, not slow ones or staying at altitude , e.g. Helios and various Lear jets..

[Australopithecus]

Maybe that’s because the pax O2 worked for more than 75% of the passengers.

This issue breaks down into a discussion when really it should be about the aircraft's ability to meet the regulations and moral imperatives to supply 100% of the iccupants with reliable O2 supply. This is just the Titanic revisited: Insufficient lifeboats=insufficienct O2 reliability.

[Beamr]

Maybe that’s because the pax O2 worked for more than 75% of the passengers.


Interesting enough, in many of the pictures/videos that have appeared in social media from airplanes with launched masks, relatively high percentage of PAX seems to either wear the mask incorrectly or not wearing it at all. Without getting to the root of this phenomenon, I believe the situation has been the same in times prior to everyone having a smart phone at hand. Considering that for average joe the situation probably comes as a surprise, they've never even seen the mask live, they've never paid attention to safety briefs and then they should assist the children, too, I reckon that during all these years and all the emergencies world wide there would've been even one case of hypoxia related death during emergency decent.

[Jumpjim]

I find this medical discussion fascinating, and educative, but very theoretical.
In my 35 years as a radar controller controlling mostly upper airspace, I had to witness a few emergency descent myself, and saw a lot more on replay.
On the ROD : except from very old types like CV990 which could put 4 reverses in flight and could go down with 10.000 ft/min, the DC8 which could put the inboards in reverse and do 6000 ft/min , most of the others did around 4000 .I never seen a 787 doing one , left before they arrived.
After the incidents occurred , except from some minor injuries ,I cannot recall anyone killed or being permanently brain damaged. I have never read anything like this on incidents reports from rest of the world either. People sucked out if seated besides the hole.. yes, but Dead by hypoxia during a descent ? But maybe someone here can find references. .
And I mean hypoxia during an emergency descent, not slow ones or staying at altitude , e.g. Helios and various Lear jets..

On the 787, assuming no structural damage and increasing the speed to Vmo/Mmo in descent from 41,000’ it takes about 3 1/2 mins to 10,000’. If you leave the speed where it is at .84 and don’t increase it assuming structural damage it takes about 5 1/2 mins for the descent. That’s with full speed brakes obviously.

[Takwis]

in descent from 41,000’ it takes about 3 1/2 mins to 10,000’.

8,800 fpm.

[golfyankeesierra]

Maybe that’s because the pax O2 worked for more than 75% of the passengers.

This issue breaks down into a discussion when really it should be about the aircraft's ability to meet the regulations and moral imperatives to supply 100% of the iccupants with reliable O2 supply. This is just the Titanic revisited: Insufficient lifeboats=insufficienct O2 reliability.
Exactly! The whole point is that Boeing, instead of sticking to the proven system, applied some new technology which got certificated by the FAA.
But contrary to everything we do in aviation, this cannot checked or tested. It is a lifesaver! How could this have passed certification?
And now apparently it has been tested, only 75% works. Doesn’t exactly return my faith in Boeing and FAA..

[vhogb]

Helios and various Lear jets..
If we add 'King Air' to your 'Lear Jet' example, there's definitely a pun there somewhere...

(Certain variants of Beech' King Air are known for their propensity to decompress very slooooowly and head off on cross-country ghost flights)

[Meester proach]

At VMO, gear extended and in a side slip, maybe. So definitely not realistic in the real life. 4000 is a correct figure.

rubbish, easily done ,

and I really wouldn’t extend the gear at VMO or do a side slip in a big jet.....back to flightsim for you.

[ATC Watcher]

8,800 fpm.
very Impressive indeed . Descending at Vmo? , the leveling off must be interesting , especially for the pax. .
@ vhogb : not many Kings in the airspace I controlled back then , but yes, heard the stories..
I was on duty in the 80s when a German Lear 25 overflew my sector at 430 , intercepted by F4s which reported an empty cockpit.. it crashed in the Atlantic when It ran out of fuel .Left an imprint in my memory...

[Takwis]

I should have clarified. I thought lots of other pilots would chime in and say, "no way". But no one did. So I will.

No Way. 4000fpm is realistic. 8800 fpm is ludicrous, for an airliner.

[etudiant]

It might be helpful if Boeing were to address this O2 system issue directly by actually testing it on one of the airline 787s. It would cost a little money, but would also show that Boeing actually is sensitive to passenger safety issues again.
Moreover, if the test is a dud, it saves Boeing from the disaster that an in flight failure would have been, allowing them to solve the problem in peacetime, as it were..

[FlightlessParrot]

Not wanting to be insistent, but may I ask again if this problem is unique to Boeing, or indeed the 787? I assume the devices come from a third-party supplier. Do all other passenger aircraft use oxygen generators instead of bottles? Is it known what the normal failure rate is?

[wiggy]

Do all other passenger aircraft use oxygen generators instead of bottles?

Can't comment of the specifics of the 787 but there certainly are other large passenger aircraft around that use gaseous oxygen/"ring main" systems.

From a users POV in the Long Haul arena they have at least a couple of possible advantages over generator systems:

1. If post decompression you end up in a brief cruise just above 10,000 feet (e.g; at say 12 000' for terrain reasons) you can selectively turn off/on supply to individual seats, thereby saving what's left in the tanks for those who are deemed to still need breathing assistance (not everybody will).

2. On a more routine basis if you have a passenger with a medical problem who needs oxygen for a considerable period of time ( and on a long haul flight it can sometimes be hours) you can supply him/her with a mask plugged into the oxygen ring main system rather than use up all your portable walk around bottles..

[Viscount Way]

[QUOTE=wiggy;10615215]Can't comment of the specifics of the 787 but there certainly are other large passenger aircraft around that use gaseous oxygen/"ring main" systems.

The 787 and certain A350's, are equipped with the Collins Aerospace (that's UTC now) PulsOx system. New technology indeed which introduces lightweight O2 cylinders along with complex, electronically controlled pyrotechnic supply valves. (the ones in question) . Operation is driven by a pcb at each seat set. This system is said to reduce system weight compared to a ring main installation. Strangely, Collins make no weight comparison with the widely used O2 generator system.
The main attraction of the O2 generator is its simplicity. Oxygen is provided by the action of the user pulling the mask downward, withdrawing a safety pin to activate the chemical reaction. Maintenance is simple; confined to checking the serviceability of the panel latches and confirming that the generator has not reached its expiry date. That very check prompted an FAA/EASA scare in 2017 when it was found that a batch of life expired generators would not work when attempts were made to dispose of them.
Most aircraft in my experience have chemical O2 generators. They seemed to have been introduced with DC10's way back when. The L1011 from the same era came with the ring main though. Which aircraft still operate with a ring main system?
Wiggy, in my old outfit it was forbidden to tap into the ring main for planned medical cases. The Stretcher Kit came complete with sufficient Therapeutic Bottles for the whole trip.

[wiggy]

Which aircraft still operate with a ring main system?

Certainly some (?all) 744s, certainly some (?all) 777s operate a ring main system (though some T7s I know of use generators in one of the cabin crew crew rest areas).

Wiggy, in my old outfit it was forbidden to tap into the ring main for planned medical cases. The Stretcher Kit came complete with sufficient Therapeutic Bottles for the whole trip.


Looks like must vary from operator to operator - FWIW where I am we are certainly allowed to tap into the ring main for medical cases if it looks like the passenger is going to need supplementary oxygen for an extended period, regardless of whether it's a pre-notified case or the crew are dealing with somebody who has fallen ill on the flight.

[Flight Alloy]

The ring main system sounds like it has some controlability at every station, does it have extra plugs for medical masks and manual activation valves for such uses?

[Rated De]

Maybe that’s because the pax O2 worked for more than 75% of the passengers.

This issue breaks down into a discussion when really it should be about the aircraft's ability to meet the regulations and moral imperatives to supply 100% of the iccupants with reliable O2 supply. This is just the Titanic revisited: Insufficient lifeboats=insufficienct O2 reliability.

Precisely.

Into every crevice at Boeing crawled the business school MBA.
Slashing with reckless abandon, never striking the vital artery, they achieved personal enrichment.

How could a proud company be denigrated to such a state where forums discuss the availability of supplemental breathing oxygen in the event of loss of cabin pressure?

Just what do these educated fools actually know?

[unobtanium]

Exactly! The whole point is that Boeing, instead of sticking to the proven system, applied some new technology which got certificated by the FAA.
But contrary to everything we do in aviation, this cannot checked or tested. It is a lifesaver! How could this have passed certification?
And now apparently it has been tested, only 75% works. Doesn’t exactly return my faith in Boeing and FAA..

Or mercury filled bulbs for logo lights, requiring a special tool and procedures to remove, store and dispose of bulbs. What the hell is wrong with the good old halogen or LED lamps? Nope, gotta use a unique and potentially dangerous mercury filled bulb.

[wiggy]

The ring main system sounds like it has some controlability at every station, does it have extra plugs for medical masks and manual activation valves for such uses?

On the aircraft I have experience of there are indeed extra outlets for medical masks at most the Passenger service units. They can be set for a high or low rate of flow (FWIW there's also a check valve to prevent flow if a mask is not plugged in).

The actual "on/off"switch to pressurise the system is on the flight deck.....

[Viscount Way]

After re-reading Collins' description of their PulsOx system I find myself a little confused by this:-

"Three duration options (small, medium and large) accommodate your aircraft’s descent profile – so you can choose the right size oxygen cylinder to get the aircraft to safety without carrying extra weight. Changing the descent profile is easy. Simply switch out the individual oxygen cylinder to the size that matches the new profile."

Can anyone with 787 experience translate this option into practical terms please? How does a flight crew know which money-saving option was adopted?

[Australopithecus]

After re-reading Collins' description of their PulsOx system I find myself a little confused by this:-

"Three duration options (small, medium and large) accommodate your aircraft’s descent profile – so you can choose the right size oxygen cylinder to get the aircraft to safety without carrying extra weight. Changing the descent profile is easy. Simply switch out the individual oxygen cylinder to the size that matches the new profile."

Can anyone with 787 experience translate this option into practical terms please? How does a flight crew know which money-saving option was adopted?

why would you need to know that? An emergency descent is flown at the speed, and hence rate of descent, at maximum or max prudent depending on perceived airframe damage. What happens subsequently is the result of engineering and cost calculations made prior by others. You can only play the hand that you are dealt.

[TURIN]

After re-reading Collins' description of their PulsOx system I find myself a little confused by this:-

"Three duration options (small, medium and large) accommodate your aircraft’s descent profile – so you can choose the right size oxygen cylinder to get the aircraft to safety without carrying extra weight. Changing the descent profile is easy. Simply switch out the individual oxygen cylinder to the size that matches the new profile."

Can anyone with 787 experience translate this option into practical terms please? How does a flight crew know which money-saving option was adopted?

FCOM?

I'm guessing it's for routine flights over high ground where a descent to a safe breathing altitude is not practical. Extended use of O2 would be required.

Not necessarily money saving, weight saving. Don't forget that Boeing promised performance and fuel savings which were difficult to meet when the structure required some redesign, which added a lot of weight.

As I said in an earlier post, this system uses smaller, lighter weight O2 bottles.
https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1080x636/_20191114_111345_de6d232849aa68a606b6a275ef408b2ff0c06923.jp g
This synoptic from the training manual may help understanding the system.

[givemewings]

chemical vs bottles varies by operator.

As far as I encountered, only B747 and A380 still use bottles (for the carriers I operated with)

Our 777 had chemical generators, 22mins duration as they did many cross-Himalayas flights.

A380 used gaseous system, with separate system for flight deck. If inadvertent activiation took place, replacing the pins into the valves at each PSU would cease oxygen flow, or it stopped automatically at 10,000' cabin alt.

Anyone else around when the 310L bottles were around with the full face mask attached? Ah, brings back memories of my first few flights...

[misd-agin]

As givemewings pointed out some aircraft have more O2 capacity for diversions over higher terrain. AIrcraft without the large O2 capacity would have 'no fly' zones to avoid the higher terrain where O2 capacity, or s/e cruise capability, couldn't ensure clearance with high terrain in the event of a depressurization or engine failure. Parts of the Andes are an example of 'no fly' zones for different aircraft types.