If one has a fuselage-borne fire situation in the cruise where the suppressants are not enough to extinguish the fire, what would happen if you (somehow...) provoked depressurisation? Would it help extinguish/retard the fire given the paucity of oxygen in cruise-level air or would it worsen things? Can you voluntarily provoke full depressurisation in the first place on modern airliners? I assume you could not do this with fully-opened pressure relief valves...
Faro
Moderators: richierich, ua900, PanAm_DC10, hOMSaR
RE: Depressurisation As Fire Extinguisher?
There are a couple of things that might interest you.
First, decompression of a passenger aircraft to extinguish a fire is pretty much only imagined in the movies. However, it has been a subject for cargo aircraft fires, which has been been the subject of at least one FAA research study which you can see here: http://www.fire.tc.faa.gov/2010Confe...lDepressurizationFreighterPres.pdf
The study (to my understanding) suggests that an intentional decompression of the aircraft does not necessarily yield great benefits in fighting a fire.
A second but related topic is smoke evacuation. This is typically used when there is a great deal of smoke in the cabin but (in general) the PIC is reasonably assured the fire is extinguished (introducing more oxygen to an unextinguished fire could be catastrophic). The B-747 in some older cabin crew manuals had a fairly unique procedure of having the flight crew descend the aircraft, depressurize the cabin and the cabin crew disarmed a main cabin door (usually two) and open it a "crack", allowing for air flow. The door handle was apparently also secured during this procedure. (Note: the cabin door is not fully opened.) Other aircraft, like the Gulfstream 550 has a dedicated "smoke evacuation" button, which in the case of the Gulfstream depressurizes a seal around the aft baggage door to allow for smoke to leave the aircraft.
The effectiveness of these techniques is somewhat questionable for smoke evacuation. A few airlines rather rely on an inflatable bag to assure clear vision in the cockpit called EVAS. You can see a video of a simulated smoke evacuation in this video (you can see the EVAS system as well) : http://youtu.be/cgIT6pkp6LQ
In summary, yes an aircraft can be manually depressurized. But doing would be exceptionally rare and for highly unusual circumstances.
[Edited 2011-10-07 01:40:36]
First, decompression of a passenger aircraft to extinguish a fire is pretty much only imagined in the movies. However, it has been a subject for cargo aircraft fires, which has been been the subject of at least one FAA research study which you can see here: http://www.fire.tc.faa.gov/2010Confe...lDepressurizationFreighterPres.pdf
The study (to my understanding) suggests that an intentional decompression of the aircraft does not necessarily yield great benefits in fighting a fire.
A second but related topic is smoke evacuation. This is typically used when there is a great deal of smoke in the cabin but (in general) the PIC is reasonably assured the fire is extinguished (introducing more oxygen to an unextinguished fire could be catastrophic). The B-747 in some older cabin crew manuals had a fairly unique procedure of having the flight crew descend the aircraft, depressurize the cabin and the cabin crew disarmed a main cabin door (usually two) and open it a "crack", allowing for air flow. The door handle was apparently also secured during this procedure. (Note: the cabin door is not fully opened.) Other aircraft, like the Gulfstream 550 has a dedicated "smoke evacuation" button, which in the case of the Gulfstream depressurizes a seal around the aft baggage door to allow for smoke to leave the aircraft.
The effectiveness of these techniques is somewhat questionable for smoke evacuation. A few airlines rather rely on an inflatable bag to assure clear vision in the cockpit called EVAS. You can see a video of a simulated smoke evacuation in this video (you can see the EVAS system as well) : http://youtu.be/cgIT6pkp6LQ
In summary, yes an aircraft can be manually depressurized. But doing would be exceptionally rare and for highly unusual circumstances.
[Edited 2011-10-07 01:40:36]
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- Starlionblue
- Posts: 21730
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RE: Depressurisation As Fire Extinguisher?
The problem is that there is plenty of oxygen even at altitude. And you risk fanning the flames.
RE: Depressurisation As Fire Extinguisher?
| Quoting Markhkg (Reply 1): However, it has been a subject for cargo aircraft fires, which has been been the subject of at least one FAA research study which you can see here |
Its more than a subject, it is in the QRH. The operating theory is that depressurizing the cabin up to FL250 will reduce the available oxygen enough to slow, if not extinguish most fires. I don't care to test this personally, but I see it mostly as measure to buy a little more time to get to an airport.
| Quoting Markhkg (Reply 1): The B-747 in some older cabin crew manuals had a fairly unique procedure of having the flight crew descend the aircraft, depressurize the cabin and the cabin crew disarmed a main cabin door (usually two) and open it a "crack", allowing for air flow. |
On the freighter version, you slow to under 200 knots and open the escape hatch in the cockpit.
RE: Depressurisation As Fire Extinguisher?
One of the issues with reducing the oxygen available to the the fire is that the fire will continue to smolder and generate heat. A re-introduction of oxygen as the aircraft descends will get the fire going again.
If the fire was in a confined area and the fire load gets really hot while it's smoldering and oxygen is quickly re-introduced it could lead to an explosive reignition (backdraft type scenario). Not likely, but very possible.
If the fire was in a confined area and the fire load gets really hot while it's smoldering and oxygen is quickly re-introduced it could lead to an explosive reignition (backdraft type scenario). Not likely, but very possible.
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- CosmicCruiser
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RE: Depressurisation As Fire Extinguisher?
Actually it's part of the checklist on the cargo jets I've flown. It worked as advertised for one of our crew a few years ago and probably saved their lives.
RE: Depressurisation As Fire Extinguisher?
Approved fire suppression in the Citation X is to depress the baggage bin.
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- CosmicCruiser
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RE: Depressurisation As Fire Extinguisher?
I should've added some of our jets now have a fire suppression system for the main cargo deck
RE: Depressurisation As Fire Extinguisher?
| Quoting CosmicCruiser (Reply 7): I should've added some of our jets now have a fire suppression system for the main cargo deck |
Is it a halon based system? I have been toying around with an idea for a main deck suppression design on my own time, that could be retrofitted, but have run into some limitations in materials technology.
RE: Depressurisation As Fire Extinguisher?
| Quoting lowrider (Reply 8): Is it a halon based system? |
FedEx is installing a foam based system. Check out this video:
http://news.van.fedex.com/firesuppressionvideo
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- Francoflier
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RE: Depressurisation As Fire Extinguisher?
| Quoting Markhkg (Reply 1): The B-747 in some older cabin crew manuals had a fairly unique procedure |
It's still on the manuals today, up to the 744. The procedure is still taught to cabin and cockpit crew alike. There is a specially designed strap that holds the door handle in a certain position to keep it ajar. One or two doors are then opened (depending on the location of the smoke) to create a draft of air to evacuate said smoke.
The procedure is only designed to evacuate smoke, and would obviously do no good in case of fire.
It is very much a last resorts measure, and I've never heard it ever being used in real life. I don't know whether the -8 offers that procedure as well.
Note that the 747 also has a 'vent' behind the overhead C/B panel in the cockpit which can be opened by the flight crew to help evacuate cockpit smoke. ...The escape hatch technique is a lot more radical and effective, if unofficial, provided you're depressurized.
As for the 744 cargo, main deck fire fighting procedure includes depressurizing the cabin to 25000 ft. As said above, it slows the fire rather than smother it. Every minute helps when you're possibly hours away from a suitable field in the middle of the Pacific ocean...
I've often wondered what would happen to a cargo fire at 35000 ft cabin altitude, but depending on what's burning, I think it still wouldn't be enough to extinguish it. And the crew wouldn't have enough O2 to stay that high long enough.
RE: Depressurisation As Fire Extinguisher?
| Quoting CosmicCruiser (Reply 5): Actually it's part of the checklist on the cargo jets I've flown. It worked as advertised for one of our crew a few years ago and probably saved their lives. |
Part of smoke evacuation process on B757 Freighters though one does not depressurize the aircraft but the aeromatic valve moves the smoke laded air out though the valve by differential pressure when the Recirculation fans are switched off.
RE: Depressurisation As Fire Extinguisher?
It's easy to depressurize an aircraft. Just turn the bleeds off supplying pressurized air.
RE: Depressurisation As Fire Extinguisher?
My understanding is that when SOP calls for depressurizing a plane it's merely for expelling fumes/smoke.
If an SR-71 can run its engines at 80K pressure altitudes, the obviously that means there's more than enough O2 for a fire anywhere else below.
If an SR-71 can run its engines at 80K pressure altitudes, the obviously that means there's more than enough O2 for a fire anywhere else below.
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- CosmicCruiser
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RE: Depressurisation As Fire Extinguisher?
Well don't forget your comparing apples and oranges. One is a wellcontrolled pressure and a sophisticated fuel and the other isn't. I can say that the procedure worked as advertised for out DC-10 crew yrs ago that landed in Newburg NY. They raised the cabin alt and the fire was subdued long enough for a ldg and exit from the jet. When the fire dept decided to manually pump open the cargo door in lieu off chopping thru the fuselage the fire flourished and the jet burned to the ground.
RE: Depressurisation As Fire Extinguisher?
| Quoting CosmicCruiser (Reply 15): I can say that the procedure worked as advertised for out DC-10 crew yrs ago that landed in Newburg NY |
CosmicCruiser, was this N68055? It is a very interesting case study, but I was surprised that the effectiveness of raising the cabin altitude wasn't really explored by the NTSB. (It would have seemed to be the perfect case study for this.)
For those interested, http://www.ntsb.gov/doclib/reports/1998/AAR9803.pdf
One of the NTSB findings interested me, "The evacuation was delayed because the flightcrew failed to ensure that the
airplane was properly depressurized."
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- CosmicCruiser
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RE: Depressurisation As Fire Extinguisher?
| Quoting Markhkg (Reply 16): "The evacuation was delayed because the flightcrew failed to ensure that the airplane was properly depressurized." |
The chklist had you essentially shut off the air to the main cargo deck but continue airflow into the cockpit, for a smoke barrier. They would still have been on O2.
RE: Depressurisation As Fire Extinguisher?
On the C-130 Emergency depresuriztion was part of Fuselage fire/Smoke and Fume elimination. If the out flow valve and safety valve couldn't depress fast enough one could pull a handle and have the center overhead emergency hatch pop out dumping the cabin pressure almost instantaniously.
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