Cabin Fire - Use of Oxygen Masks
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Cabin Fire - Use of Oxygen Masks
This week the Air Crash Investigations episode that was shown (here in Australia) depicted the Air Canada DC9 emergency landing at Cincinnati airport in 1983.
As someone interested in civil aviation and aviation crash investigations, I enjoy watching this show. I appreciate that licensed pilots may not find it entirely accurate and it is after all dramatised for TV. I would however hope that there is a fair amount of truth that goes into each episode.
My question relates to the decision of the pilots not to drop the oxygen masks in the passenger cabin. This was after the fire had been burning and the smoke visible for a considerable amount of time. The cabin, towards the latter part of the flight, was depicted as being filled with the noxious/poisonous smoke, and as a result the passengers had tremendous difficulty breathing (choking, coughing, etc).
The documentary mentioned the non-deployment of the oxygen masks, and there were several comments/interviews with the actual PIC (who survived) that were conducted for this episode. The PIC commented that he didn't deploy the oxygen masks, because he is only allowed to in the event of decompression (or perhaps they deploy automatically?)
It seems ironic that the PIC was subsequently shown putting on his emergency oxygen mask in the cockpit.
The coroner found most (or all) of the deceased had excessive amounts of Carbon Monoxide (and other poisons) in their blood.
So I'm just wondering - was there really a rule that prevented pilots from dropping the oxygen masks in this type of situation? Is such a rule still in place? Is such a rule sensible? And why does it exist?
Any feedback is greatly appreciated.
As someone interested in civil aviation and aviation crash investigations, I enjoy watching this show. I appreciate that licensed pilots may not find it entirely accurate and it is after all dramatised for TV. I would however hope that there is a fair amount of truth that goes into each episode.
My question relates to the decision of the pilots not to drop the oxygen masks in the passenger cabin. This was after the fire had been burning and the smoke visible for a considerable amount of time. The cabin, towards the latter part of the flight, was depicted as being filled with the noxious/poisonous smoke, and as a result the passengers had tremendous difficulty breathing (choking, coughing, etc).
The documentary mentioned the non-deployment of the oxygen masks, and there were several comments/interviews with the actual PIC (who survived) that were conducted for this episode. The PIC commented that he didn't deploy the oxygen masks, because he is only allowed to in the event of decompression (or perhaps they deploy automatically?)
It seems ironic that the PIC was subsequently shown putting on his emergency oxygen mask in the cockpit.
The coroner found most (or all) of the deceased had excessive amounts of Carbon Monoxide (and other poisons) in their blood.
So I'm just wondering - was there really a rule that prevented pilots from dropping the oxygen masks in this type of situation? Is such a rule still in place? Is such a rule sensible? And why does it exist?
Any feedback is greatly appreciated.
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So, it's OK for the PIC to use his oxygen mask, but not for the passengers? Perhaps better to let them die from smoke inhalation?
And I wouldn't have considered that passengers using the emergency oxygen supply through masks (ie a closed system) akin to adding oxygen to a fire, in the sense that opening the doors upon landing ultimately did.
Thanks for your great help HON1R - perhaps have a read of what is described below "Spectators Balcony (Spotters Corner)" on the home page.
And I wouldn't have considered that passengers using the emergency oxygen supply through masks (ie a closed system) akin to adding oxygen to a fire, in the sense that opening the doors upon landing ultimately did.
Thanks for your great help HON1R - perhaps have a read of what is described below "Spectators Balcony (Spotters Corner)" on the home page.
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No "rule" exists prohibiting a pilot from deploying oxygen masks, but procedures do exist by which crews operate in any type of abnormal or emergency situation.
While a cabin oxygen mask does provide supplementary oxygen, it also combines the oxygen with cabin air...meaning that passengers who are drawing oxygen through the mask are also breathing in cabin smoke.
The masks can be prevented from drawing anything but oxygen...but they don't have a facial fit, knowledge of the mask is required, and the 02 supply doesn't deliver air for a complete breath; it's supplementary oxygen, to add to the cabin air that the passenger is breathing. That's all.
Oxygen systems come in different varieties. Some aircraft use chemical canisters which get very hot and generate oxygen. Others use oxygen stored in containers under pressure. If a cabin fire exists which is burning near oxygen lines, pressurizing the lines may provide an additional unwarranted hazard. Activating oxygen canisters may also provide an additional hazard.
Under some conditions oxygen will be provided, but under others, it will not. The abnormal and emergency procedures are written, and used, for a reason.
While a cabin oxygen mask does provide supplementary oxygen, it also combines the oxygen with cabin air...meaning that passengers who are drawing oxygen through the mask are also breathing in cabin smoke.
The masks can be prevented from drawing anything but oxygen...but they don't have a facial fit, knowledge of the mask is required, and the 02 supply doesn't deliver air for a complete breath; it's supplementary oxygen, to add to the cabin air that the passenger is breathing. That's all.
Oxygen systems come in different varieties. Some aircraft use chemical canisters which get very hot and generate oxygen. Others use oxygen stored in containers under pressure. If a cabin fire exists which is burning near oxygen lines, pressurizing the lines may provide an additional unwarranted hazard. Activating oxygen canisters may also provide an additional hazard.
Under some conditions oxygen will be provided, but under others, it will not. The abnormal and emergency procedures are written, and used, for a reason.
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Thanks SNS3Guppy.
So you reckon that's what happened with Air Canada 797? (In terms of the dangers of using the oxygen masks in a fire).
It would be interesting to know, therefore, the procedure in the instance of a fire and an emergency decompression.
So you reckon that's what happened with Air Canada 797? (In terms of the dangers of using the oxygen masks in a fire).
It would be interesting to know, therefore, the procedure in the instance of a fire and an emergency decompression.
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Malcom,
I am not familiar with the circumstances regarding the DC9 flight, and can't comment on that. You've indicated that the captain stated he followed the appropriate procedures. For now, that's enough.
Your original question appears to be why the crew dons masks and uses oxygen, while it's not provided to the passengers. Let's tackle that one first.
The masks we use in the cockpit are different than the masks used by passengers. The passenger masks are designed to provide a limited amount of supplementary oxygen, which is mixed with cabin air, in order to sustain life during an emergency descent. This is the only application for the use of oxygen by passengers; during a time when cabin pressure has been reduced and oxygen is an immediate lifesaving requirement, it's provided on an emergency-only basis, for a brief period of time.
This doesn't, as a rule, do anything for a passenger during a smoke or fire situation, as the passenger is breathing the cabin air. The same acids which attack mucus membranes in the nose, eyes, and mouth, still cause the stinging and burning. The same toxic vapors enter the airway, with or without the passenger mask.
The cockpit crew goes on oxygen quite simply because without the crew being able to see and breathe, everybody dies. It's in everybody's interest for the crew to be on oxygen.
In the cockpit, we wear a mask which completely seals. It prevents any vapors, fumes, smoke, or other dangerous aerosols from entering the mask when we breathe. We have several settings on these masks, one of which does the same as the passenger masks...it dilutes the oxygen intake with cabin air in order to prolong the duration of the available oxygen.
The other two mask regulator settings, however, don't use the cabin air at all. One is a 100% setting, and the other is an emergency setting in which not only is 100% oxygen delivered, but it's delivered under pressure, forcing air into our lungs in some systems, and in others providing adequate pressure to prevent any intrusion of outside gasses.
Over these masks a pair of smoke goggles can be worn. Some aircraft also use a special inflatable hood which goes between the windscreen and the pilot to enable the pilot to see out of the aircraft even when the cockpit is full of smoke.
Bear in mind these systems are in airline and corporate type aircraft. Not all aircraft have these features. I landed in a single engine airplane a few years ago, that was on fire, with a cockpit full of smoke, and couldn't see as I rolled out on the runway due to the smoke and the burning in my eyes. I had to open a small side window to get any relief, and couldn't use it because my helmet was in the way.
You also asked about a situation involving a "decompression" or depressurization. I've experienced a rapid depressurization, though not at a high altitude, and didn't need or use the mask at that time. In most cases, it's used immediately; in my case the failure was a door seal which blew out and created a lot of noise and a pressure loss. Only a very brief descent was required, and a bigger concern was the inability to hear air traffic control due to the noise at the time. The even to occured in a corporate type airplane during a repositioning flight without passengers.
You asked about a situation involving a depressurization and a fire. This is certainly a possible, albeit very unlikely situation. In most systems, the cabin masks will drop and be ready for oxygen delivery when cabin pressure drops low enough to activate a pressure switch. This typically takes place when cabin pressure climbs through about 14,000'. When this occurs, the pilot action isn't required; the masks drop on their own.
A side benefit to a pressure loss during some type of cabin or cargo fire is that fires don't burn well when atmospheric pressure is low. In fact, at a high altitude, a loss of cabin pressure may extinguish the fire...and is a legitimate firefighting technique in rare emergency circumstances. In the very unusual case of a fire and loss of cabin pressure, the masks will be automatic, and in most cases an emergency descent will performed to a lower altitude.
We do have some procedures for keeping the oxygen on and leveling at an intermediate altitude, around 25,000', when flight conditions preven us from going lower. Such a situation might be an oceanic flight when we can't go very low (because more fuel is consumed at low altitudes), and still have a long way to go. The lower altitude is a compromise between rapid flight to the destination, fuel consumption, and safety. Also a very rare potential situation, very unlikely.
I understand your concern...passengers coughing, choking. This occurs as a result of an airway irritant such as smoke. However, dropping oxygen masks won't fix this, because the passenger will still be getting the smoke with each breath...and it's still going to attack other mucus membranes such as the eyes and nose.
The answer is to do everything possible to prevent such a situation from occurring...and prevention works well, because inflight fires are very rare. When smoke in the cabin or cockpit does occur, in most cases it's handled efficiently by crew coordination and published procedures, and ends uneventfully. Rest assured that when an abnormal or emergency situation happens, it's not the time for the crew to start trying to invent a procedure or guess at what we must do; we train for these events regularly (even though they happen very rarely). When such an event does occur, we follow our training and procedures very closely because these are the most effective, and provide the greatest opportunity to end the situation in a satisfactory manner.
I am not familiar with the circumstances regarding the DC9 flight, and can't comment on that. You've indicated that the captain stated he followed the appropriate procedures. For now, that's enough.
Your original question appears to be why the crew dons masks and uses oxygen, while it's not provided to the passengers. Let's tackle that one first.
The masks we use in the cockpit are different than the masks used by passengers. The passenger masks are designed to provide a limited amount of supplementary oxygen, which is mixed with cabin air, in order to sustain life during an emergency descent. This is the only application for the use of oxygen by passengers; during a time when cabin pressure has been reduced and oxygen is an immediate lifesaving requirement, it's provided on an emergency-only basis, for a brief period of time.
This doesn't, as a rule, do anything for a passenger during a smoke or fire situation, as the passenger is breathing the cabin air. The same acids which attack mucus membranes in the nose, eyes, and mouth, still cause the stinging and burning. The same toxic vapors enter the airway, with or without the passenger mask.
The cockpit crew goes on oxygen quite simply because without the crew being able to see and breathe, everybody dies. It's in everybody's interest for the crew to be on oxygen.
In the cockpit, we wear a mask which completely seals. It prevents any vapors, fumes, smoke, or other dangerous aerosols from entering the mask when we breathe. We have several settings on these masks, one of which does the same as the passenger masks...it dilutes the oxygen intake with cabin air in order to prolong the duration of the available oxygen.
The other two mask regulator settings, however, don't use the cabin air at all. One is a 100% setting, and the other is an emergency setting in which not only is 100% oxygen delivered, but it's delivered under pressure, forcing air into our lungs in some systems, and in others providing adequate pressure to prevent any intrusion of outside gasses.
Over these masks a pair of smoke goggles can be worn. Some aircraft also use a special inflatable hood which goes between the windscreen and the pilot to enable the pilot to see out of the aircraft even when the cockpit is full of smoke.
Bear in mind these systems are in airline and corporate type aircraft. Not all aircraft have these features. I landed in a single engine airplane a few years ago, that was on fire, with a cockpit full of smoke, and couldn't see as I rolled out on the runway due to the smoke and the burning in my eyes. I had to open a small side window to get any relief, and couldn't use it because my helmet was in the way.
You also asked about a situation involving a "decompression" or depressurization. I've experienced a rapid depressurization, though not at a high altitude, and didn't need or use the mask at that time. In most cases, it's used immediately; in my case the failure was a door seal which blew out and created a lot of noise and a pressure loss. Only a very brief descent was required, and a bigger concern was the inability to hear air traffic control due to the noise at the time. The even to occured in a corporate type airplane during a repositioning flight without passengers.
You asked about a situation involving a depressurization and a fire. This is certainly a possible, albeit very unlikely situation. In most systems, the cabin masks will drop and be ready for oxygen delivery when cabin pressure drops low enough to activate a pressure switch. This typically takes place when cabin pressure climbs through about 14,000'. When this occurs, the pilot action isn't required; the masks drop on their own.
A side benefit to a pressure loss during some type of cabin or cargo fire is that fires don't burn well when atmospheric pressure is low. In fact, at a high altitude, a loss of cabin pressure may extinguish the fire...and is a legitimate firefighting technique in rare emergency circumstances. In the very unusual case of a fire and loss of cabin pressure, the masks will be automatic, and in most cases an emergency descent will performed to a lower altitude.
We do have some procedures for keeping the oxygen on and leveling at an intermediate altitude, around 25,000', when flight conditions preven us from going lower. Such a situation might be an oceanic flight when we can't go very low (because more fuel is consumed at low altitudes), and still have a long way to go. The lower altitude is a compromise between rapid flight to the destination, fuel consumption, and safety. Also a very rare potential situation, very unlikely.
I understand your concern...passengers coughing, choking. This occurs as a result of an airway irritant such as smoke. However, dropping oxygen masks won't fix this, because the passenger will still be getting the smoke with each breath...and it's still going to attack other mucus membranes such as the eyes and nose.
The answer is to do everything possible to prevent such a situation from occurring...and prevention works well, because inflight fires are very rare. When smoke in the cabin or cockpit does occur, in most cases it's handled efficiently by crew coordination and published procedures, and ends uneventfully. Rest assured that when an abnormal or emergency situation happens, it's not the time for the crew to start trying to invent a procedure or guess at what we must do; we train for these events regularly (even though they happen very rarely). When such an event does occur, we follow our training and procedures very closely because these are the most effective, and provide the greatest opportunity to end the situation in a satisfactory manner.
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Many thanks SNS3Guppy for your long and detailed posting.
I certainly wasn't aware about the majority of what you have mentioned.
With the Air Canada Flight 797 incident, 23 out of the 41 passengers and crew died. As I mentioned on one of my earlier threads, the ACI episode mentions that the coroner's report stated many (if not all) of the deceased had extreme levels of CO3 and other noxious gasses in their bloodstreams. So it's reasonable to assume that some, if not many of the deceased may have been dead prior to landing and were therefore not killed by the fire itself.
I was left with the impression that, had the flight needed to continue for another 5 or 10 minutes, none of the passengers nor cabin crew may have survived. So imagine the disbelief of the PIC and F/O upon making a safe landing if this had eventuated.
Your post has certainly explained well why oxygen masks are not deployed in the cabin in the event of fire, and how useless they'd be if they were. And in this sense, it seems that things are not a lot different in 1983 compared to 2009. I guess it then begs the question, if the equipment/technology is available (as in what is used in the cockpit), then why aren't they used in the cabin area?
The obvious answer is cost. Perhaps $5-10K per mask, including all fittings etc, so may well be in the 7 figures for an entire aircraft (say a 737 or Airbus A320). Unless there's any other logical reasons.
As you've mentioned, inflight fires are very rare. The ACI episode, and internet websites, mention several areas of improvements that were made as a result of the flight 797 incident. They mentioned changes to the materials that were used as aircraft furnishings; lights in the aisle that indicated the exit; installing smoke detectors in all toilets; and improved firefighting training and equipment to crew. (Amongst other things).
I guess the fact that, over most (or all?) of the world, smoking has been gradually phased out in all passenger aircraft over the past 25 years - which I would have to take it would have lessened the likelihood of cabin fires in this time.
I certainly wasn't aware about the majority of what you have mentioned.
With the Air Canada Flight 797 incident, 23 out of the 41 passengers and crew died. As I mentioned on one of my earlier threads, the ACI episode mentions that the coroner's report stated many (if not all) of the deceased had extreme levels of CO3 and other noxious gasses in their bloodstreams. So it's reasonable to assume that some, if not many of the deceased may have been dead prior to landing and were therefore not killed by the fire itself.
I was left with the impression that, had the flight needed to continue for another 5 or 10 minutes, none of the passengers nor cabin crew may have survived. So imagine the disbelief of the PIC and F/O upon making a safe landing if this had eventuated.
Your post has certainly explained well why oxygen masks are not deployed in the cabin in the event of fire, and how useless they'd be if they were. And in this sense, it seems that things are not a lot different in 1983 compared to 2009. I guess it then begs the question, if the equipment/technology is available (as in what is used in the cockpit), then why aren't they used in the cabin area?
The obvious answer is cost. Perhaps $5-10K per mask, including all fittings etc, so may well be in the 7 figures for an entire aircraft (say a 737 or Airbus A320). Unless there's any other logical reasons.
As you've mentioned, inflight fires are very rare. The ACI episode, and internet websites, mention several areas of improvements that were made as a result of the flight 797 incident. They mentioned changes to the materials that were used as aircraft furnishings; lights in the aisle that indicated the exit; installing smoke detectors in all toilets; and improved firefighting training and equipment to crew. (Amongst other things).
I guess the fact that, over most (or all?) of the world, smoking has been gradually phased out in all passenger aircraft over the past 25 years - which I would have to take it would have lessened the likelihood of cabin fires in this time.
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The obvious answer is cost. Perhaps $5-10K per mask, including all fittings etc, so may well be in the 7 figures for an entire aircraft (say a 737 or Airbus A320). Unless there's any other logical reasons.
The masks we use have microphones installed, are fitted before each flight (depending on the system in use), are quite expensive, use larger hoses, and in many cases, dedicated receptacles which of themselves are advanced pieces of equipment.
Crew oxygen comes from compressed gas oxygen cylinders. In many airline aircraft today, the masks are fed by oxygen generators; canisters that preclude the need for heavy cylinders and the weight of additional lines and tubing, regulators, etc. This is a space saving and weight saving issue, and weight is a very critical issue on any aircraft. To install enough oxygen cylinders to a large airplane to serve all the passengers for the necessary duration of the flight and the same types of masks available in the cockpit wouldn't be practical.
There are smoke hoods and filters available on the market which you can put in your carry-on gear, such as the Evacu8 system...not much bigger than a soda can (EVAC-U8 Smoke Hood-$75.00), that can be used in an emergency. They serve to protect your eyes and your airway. Some places won't let you have one on board, some will. Ironically, my own company crew policy prohibits the carriage or use of such systems.
