Right....
Google CPAP...

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.....

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

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.

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.

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.

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.

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' from 2006, states this:
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.

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?

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 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

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.

Cabin O2 masks are certified up to 25.000 ft.

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 ?

MechEngr

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..

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.

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.

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...

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.

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.

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..

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.

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.

8,800 fpm.

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..

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)

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.

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...

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.

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..

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?

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..

PulsOx Emergency O2 System
 

[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.

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).

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.

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?

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?