Qantas 744 Depressurisation
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Attn Pacplyer,
Can I point out that pure Oxygen does not burn or explode so it makes no sense to talk about the oxygen leaking, finding a source of ignition and exploding. If you toss a lighted match in a room full of oxygen.. the match will burn faster and use up some of the oxygen but once the match is all burnt up the fire goes out. The Oxygen will NOT explode or burn.
Now if the bottle had been filled with hydrogen by mistake and that leaked then it would be a very different matter. No evidence for that though.
Can I point out that pure Oxygen does not burn or explode so it makes no sense to talk about the oxygen leaking, finding a source of ignition and exploding. If you toss a lighted match in a room full of oxygen.. the match will burn faster and use up some of the oxygen but once the match is all burnt up the fire goes out. The Oxygen will NOT explode or burn.
Now if the bottle had been filled with hydrogen by mistake and that leaked then it would be a very different matter. No evidence for that though.
Second Law
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Blacksheep 667
No I can't find reference to any such cylinder failure either, and I guess like you too, have looked assiduously.
I can't even find such a (spontaneous?) failure documented at ground level.
I have worked with, on and off so to speak, a variety of compressed gases (O2, N2, H2, CO2, C2H4, C2H2) over the years.
For the record, the vent hole on all the cylinders I have come across is set at an angle (not sure of exact angle, apparently it can vary). This makes sure that you don't get a 180 degree staight line torpedo in the event of a catastrophic valve assembly failure eg cylinder being dropped from height on a building site. What this means is you get a high speed circular path if the top gets ripped off.
Are the various gas cylinders in use on aircraft engineered in the same way I wonder? I can't find that either.
CW
No I can't find reference to any such cylinder failure either, and I guess like you too, have looked assiduously.
I can't even find such a (spontaneous?) failure documented at ground level.
I have worked with, on and off so to speak, a variety of compressed gases (O2, N2, H2, CO2, C2H4, C2H2) over the years.
For the record, the vent hole on all the cylinders I have come across is set at an angle (not sure of exact angle, apparently it can vary). This makes sure that you don't get a 180 degree staight line torpedo in the event of a catastrophic valve assembly failure eg cylinder being dropped from height on a building site. What this means is you get a high speed circular path if the top gets ripped off.
Are the various gas cylinders in use on aircraft engineered in the same way I wonder? I can't find that either.
CW
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No probs NSEU,
I understand the risks of hi pressure O2 and it's ability to ignite even alloys. Some years ago Continental forbid us to replenish systems whilst cylinders were onboard. They were a bit 'edgey' after they lost an ACFT (due to fire) during onboard replenishment.
Anyway, I just like to burn things so i'll still go ahead with my little T9 flammablity test!!!
I understand the risks of hi pressure O2 and it's ability to ignite even alloys. Some years ago Continental forbid us to replenish systems whilst cylinders were onboard. They were a bit 'edgey' after they lost an ACFT (due to fire) during onboard replenishment.
Anyway, I just like to burn things so i'll still go ahead with my little T9 flammablity test!!!
Last edited by Aerolex; 30th Jul 2008 at 12:31.
Interesting photo from Machaca. Like Ripline, I find the restraint and lack of protection of these cylinders quite surprising. Machaca suggests a cylinder failure might have caused the cylinder to pivot to the angle shown. What if a prior failure of restraint or to properly restrain had allowed the cylinder to lie in the position shown, thereby exposing the valve mechanism (always the weak point of a compressed gas container) to be exposed to being whacked by a ULD on one or more occasions. It would be interesting to know the clearances. The comments by Mr Walsh on the ABC website suggest that this is one of many avenues being covered. As many have remarked on this forum, spontaneous explosion of the cylinder body would presumably have left far more debris and wider damage.
Oxygen cylinder at fault in Qantas emergency: ATSB - ABC News (Australian Broadcasting Corporation)
Oxygen cylinder at fault in Qantas emergency: ATSB - ABC News (Australian Broadcasting Corporation)
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cwatters:
Thanks for that. So by itself, an accumulated concentration of oxygen in a chamber doesn't have the potential to ignite with an explosive force; is that what you're saying?
It must be combined with another element (like hydrogen from a venting battery) to explode?
Though I have never witnessed it, I have read reports in Aviation Safety and Aviation accident classes of personnel burning to death from oxygen soaked clothing. But that is a simple burning process, not an expansion by itself I guess. The crew of apollo one/seven Grissom, White and Caffie experienced an intense rapid fire in the presence of 100% oxygen on the launchpad most likely ignited by a spark from electrical equipment. Nobody could get near it, but I don't recall an explosion except secondary bottles going off If I remember correctly.
But I think what you say is true now that I think about it.
Oxygen by itself is not an explosion hazard; so the leak/bang theory is not plausible without another catalyst of some sort.
Good group on this board... and thanks cwatters for straightening me out on that.
[added: So pure oxygen leaking is a hazardous oxidizer looking for a fuel source. Would you buy that?]
[I have modified my previous posts to include that omission of this theory]
Thanks for that. So by itself, an accumulated concentration of oxygen in a chamber doesn't have the potential to ignite with an explosive force; is that what you're saying?
It must be combined with another element (like hydrogen from a venting battery) to explode? Though I have never witnessed it, I have read reports in Aviation Safety and Aviation accident classes of personnel burning to death from oxygen soaked clothing. But that is a simple burning process, not an expansion by itself I guess. The crew of apollo one/seven Grissom, White and Caffie experienced an intense rapid fire in the presence of 100% oxygen on the launchpad most likely ignited by a spark from electrical equipment. Nobody could get near it, but I don't recall an explosion except secondary bottles going off If I remember correctly.
But I think what you say is true now that I think about it.
Oxygen by itself is not an explosion hazard; so the leak/bang theory is not plausible without another catalyst of some sort.
Good group on this board... and thanks cwatters for straightening me out on that.
[added: So pure oxygen leaking is a hazardous oxidizer looking for a fuel source. Would you buy that?]
[I have modified my previous posts to include that omission of this theory]
Last edited by pacplyer; 30th Jul 2008 at 12:49.
The Reverend
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Max Tow,
It would be extremely difficult to whack any part of the Oxygen system by a ULD as none of it protrudes outside the vertical ribs and covered by panels in the cargo compartment. Have you ever observed the loading of ULDs in the cargo hold? PDUs (Power Drive Units) propel the ULDs along retractable guide rails into the required load position. The ULDs are shape designed to suit the shape of the cargo hold sidewalls and there is no danger of penetration of panels or curtains and interference with oxygen, cargo fire bottles, cabin pressure relief valves or potable water tanks, which they cover.
thereby exposing the valve mechanism (always the weak point of a compressed gas container) to be exposed to being whacked by a ULD on one or more occasions.
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Apologies if this has already been mentioned, but would it not be a good idea if the cabin crew mentioned the likelihood of a rapid descent in the event of the oxygen masks being deployed during the safety demonstration, thus depriving the media of the "plummeting towards the ground" stories?
Some people seem to think that flying around in a metal cylinder at 800kph is perfectly safe
N4790P
Some people seem to think that flying around in a metal cylinder at 800kph is perfectly safe
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a small number of masks did not deploy from the passenger modules
Also, 346 passengers, but 418 masks activated - something clearly wasn't right.
[ Well, we know something wasn't right since one cyclinder had decided to exit through the hull, so clearly the system was compromised. Questions will be around did it perform as expected/designed in the event of a cylinder going awol. ]
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Is it pure Oxygen? if so why is this used and not air?
I assume to get the same amount of oxygen into the passengers' lungs using compressed air, the bottles would have to be 5 times as big.... so there'd be a big weight/space penalty. The air we breath at sea level is 20% oxygen.
And wouldn't any gas under the same pressure be just as "propellant"?
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Is it pure Oxygen? if so why is this used and not air?
A person breathing normal air at sea level has no problems
A person breathing normal air at 30,000 feet can't get enough oxygen into his/her lungs because the air is far less dense.
Applying pure oxygen would increase the percentage of oxygen molecules per ambient air molecules at the lower density, thus maintaining breathable levels.
Incidentally, if compressed air was used, as soon as it left the regulator it would have the same density as the ambient air and would make no difference.
RB
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HotDog,
What if the baggage that you can see in the many pictures of the hole, was pallet loaded? I have seen plenty of cargo hold lining damage (a check prior to ETOPS departures) made by ULD's whilst loading. The cargo liner is not particularly thick and the O2 bottles are covered by a fabric curtain.
What if the baggage that you can see in the many pictures of the hole, was pallet loaded? I have seen plenty of cargo hold lining damage (a check prior to ETOPS departures) made by ULD's whilst loading. The cargo liner is not particularly thick and the O2 bottles are covered by a fabric curtain.
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If you mean after an emergency landing / crash, then that is already in the saftey cards (at least the ones I can remember). If you mean in-flight, then I would advise caution - if you keep leaning over to the windows to check the wings, sooner or later someone is going to ask why, and explaining that you are "checking if it is on fire" might well get misunderstood these days.
Might not be a bad idea, there have been a number of crashes where people have survived the impact (with survivable injuries) and died of exposure. On the other hand if you were properly dressed and equiped for survival, you won't get get through security in the first place. Maybe the lifejackets should all have a survival kit attached - say foil blanket, firelighters, flares, knife, etc. 
On the shoes and trousers bit, a friend of mine, if he had had his own way, would have banned anyone not properly dressed for survival.
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Originally Posted by Ripline
SLF Alert....
With reference to Machaca's picture on post #703, I'm amazed that there only appears to be one retaining strap near the tank neck. Given the potential for stored energy to move the cylinder mass around this pivot point (as he illustrates) is this the only mechanism used to stop it going walkies? I would have expected at least a lower cup support or a rear vertical spine plus a lower strap system.
Not exactly relevant I know but I wouldn't dream of flying a hot air balloon without two strapping systems on the flight cylinders - and my landings are (usually) not much more violent than a 747's arrival.
I only ask 'cos I'm interested.
Ripline
With reference to Machaca's picture on post #703, I'm amazed that there only appears to be one retaining strap near the tank neck. Given the potential for stored energy to move the cylinder mass around this pivot point (as he illustrates) is this the only mechanism used to stop it going walkies? I would have expected at least a lower cup support or a rear vertical spine plus a lower strap system.
Not exactly relevant I know but I wouldn't dream of flying a hot air balloon without two strapping systems on the flight cylinders - and my landings are (usually) not much more violent than a 747's arrival.
I only ask 'cos I'm interested.
Ripline
I've no idea about the validity of the latter, but you and I were both taught by the short round chap of the risks associated with the former assumption...
The Reverend
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Litebulbs, if they load a pallet which is assembled to strict qualifications regarding content and shape, it is still guided into it's designated position by the mechanised loading system; same as the ULDs. Further more, a pallet is a flat piece of metal of approximately 2cm thickness. The neck of an oxygen bottle is about 2/3 up the sidewall of the cargo compartment. If you are familiar with loading cargo, you would also know that once in the desired position as per load sheet, ULDs, pallets, are secured by pallet locks which prevents any shift of cargo until unlocked. I have many hours in my logbook, flying freight; main deck and lower. I do wish however, that a professional loadmaster would voice an opinion on this subject, bless their souls; not many of them left these days in aviation.
Hotdog
As you say, nothing should protrude if everything is where it ought to be - my query was whether the gap between curtain & ULD/pallet was small enough such that a loose cylinder still on its stand but leaning into the curtain would bulge outwards enough to be hit at its extremity (i.e. the valve) during loading. Like Litebulb, I've seen plenty of cargo being loaded and plenty of sidewall damage but am unfamiliar with how generous are the 747 lower deck clearances. I guess the point is that (as the ATSB seem to imply) it's thankfully almost unheard of for a cylinder to just explode without a degree of provocation, & that the valve area is the inherent weakspot.
PS Infrequent Flyer 789: "Also, 346 passengers, but 418 masks activated - something clearly wasn't right." You expect a serious answer to that? Must have been a failure of the bumonseatsensor....
As you say, nothing should protrude if everything is where it ought to be - my query was whether the gap between curtain & ULD/pallet was small enough such that a loose cylinder still on its stand but leaning into the curtain would bulge outwards enough to be hit at its extremity (i.e. the valve) during loading. Like Litebulb, I've seen plenty of cargo being loaded and plenty of sidewall damage but am unfamiliar with how generous are the 747 lower deck clearances. I guess the point is that (as the ATSB seem to imply) it's thankfully almost unheard of for a cylinder to just explode without a degree of provocation, & that the valve area is the inherent weakspot.
PS Infrequent Flyer 789: "Also, 346 passengers, but 418 masks activated - something clearly wasn't right." You expect a serious answer to that? Must have been a failure of the bumonseatsensor....
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Infrequentflyer789,
I don't understand your argument...
The point I was attempting to make is that 'the media are a bunch of wnkrs.
There was no 'plunge' or 'plummet' nor was there a critical issue with O2 masks.
FYI when testing O2 systems on RPT ACFT (in Australia anyway) there is a certain number of masks that are permitted not to deploy. The key thing here is that the masks that don't deploy should not be adjacent to each other.
Being an 'infrequent flyer' you might not be aware that there are extra masks in every PSU (pax service unit: above your head). For example, the 3 seats outboard of a 747, there will be 4 masks drop from the PSU in a depresurisation event. Plenty of masks for all even if yours dont drop.
The location of where the masks failed to deploy will be the issue, not the number, trust me.
As far as numbers go, 418 out of 484 masks for 346 PAX sounds pretty good to me.
I don't understand your argument...
The point I was attempting to make is that 'the media are a bunch of wnkrs.
There was no 'plunge' or 'plummet' nor was there a critical issue with O2 masks.
FYI when testing O2 systems on RPT ACFT (in Australia anyway) there is a certain number of masks that are permitted not to deploy. The key thing here is that the masks that don't deploy should not be adjacent to each other.
Being an 'infrequent flyer' you might not be aware that there are extra masks in every PSU (pax service unit: above your head). For example, the 3 seats outboard of a 747, there will be 4 masks drop from the PSU in a depresurisation event. Plenty of masks for all even if yours dont drop.
The location of where the masks failed to deploy will be the issue, not the number, trust me.
As far as numbers go, 418 out of 484 masks for 346 PAX sounds pretty good to me.
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LoL Hotdog,
The real world is different imho. I've had flights where the 2cm steel pallets were stacked to the ceiling and burned out the smart wheels on a freighter because they were so heavy (they were pushed by a forklift on the ground the top ones rotated sticking them into the thin fiberglass liner of the compartment. I've had cargo build ups fall over in turbulence.
I had one flight (A310) where almost all the floor/pallet locks were forgotten in the lower hold, and it sounded like a subway/then a crash even way up in the cockpit everytime we changed deck angle/power. Sent the F/O down to investigate. It ruined his white shirt! (but he got all the locks up.)
Yes, the real world is something different all together. I still agree with you that it seems unlikely that a puncture could damage something in that location, but who knows what's been going on down there unsupervised during loading?
Stuff happens.
SLF hear strange bangs in the night! Contract people scamper off with their tail between their legs and don't tell anybody because they don't want to get canned.
Those reality things said, I should point out that I feel Qantas is a great airline staffed by exceptional pros. If I had to put my family on an airline, it wouldn't be Kor or Dynasty, that's for sure; it'd be Qantas!
The real world is different imho. I've had flights where the 2cm steel pallets were stacked to the ceiling and burned out the smart wheels on a freighter because they were so heavy (they were pushed by a forklift on the ground the top ones rotated sticking them into the thin fiberglass liner of the compartment. I've had cargo build ups fall over in turbulence.
I had one flight (A310) where almost all the floor/pallet locks were forgotten in the lower hold, and it sounded like a subway/then a crash even way up in the cockpit everytime we changed deck angle/power. Sent the F/O down to investigate. It ruined his white shirt! (but he got all the locks up.)
Yes, the real world is something different all together. I still agree with you that it seems unlikely that a puncture could damage something in that location, but who knows what's been going on down there unsupervised during loading?
Stuff happens.
SLF hear strange bangs in the night! Contract people scamper off with their tail between their legs and don't tell anybody because they don't want to get canned.
Those reality things said, I should point out that I feel Qantas is a great airline staffed by exceptional pros. If I had to put my family on an airline, it wouldn't be Kor or Dynasty, that's for sure; it'd be Qantas!
The Reverend
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Max TOW, review post #519 on page 26 and post # 621 on page 32.
pacplyer, I don't doubt you at all. However it would help if you had added operator location. Africa maybe? I am pretty certain this situation would not be allowed to occur on a Qantas aeroplane and it certainly did not have anything to do with with the depressurisation incident. The missing bottle was not in the vertical stack on the starboard side of the LFW cargo hold but a horizontally mounted bottle at approximately STA880, aft and above the loading zone.
pacplyer, I don't doubt you at all. However it would help if you had added operator location. Africa maybe? I am pretty certain this situation would not be allowed to occur on a Qantas aeroplane and it certainly did not have anything to do with with the depressurisation incident. The missing bottle was not in the vertical stack on the starboard side of the LFW cargo hold but a horizontally mounted bottle at approximately STA880, aft and above the loading zone.