Emergency Oxygen Ordered Removed From Lavatories

Tue, Mar 22, 2011 — David Evans

Featured, Regulatory & Other Items

The FAA has already initiated action to nullify the emergency oxygen supply to aircraft lavatories, but the reasons for this hasty action are not stated. Furthermore, the FAA’s own Technical Center reports indicate that an activated oxygen generator does not generate enough heat to ignite cardboard or other packing materials.

Significant Regulatory & Related Activity


8 March 2011                   Federal Aviation Administration (FAA)

FR Doc 2011-5292         Docket No. FAA-2011-0157

AD 2011-04-09

Final Rule — Various Transport Category Airplanes Equipped With Chemical Oxygen Generators Installed in a Lavatory

Prior comment by those flying on the nation’s airliners was deemed “contrary to the public interest” and the FAA on 10 February 2011 secretly ordered the “hazard” posed by chemical oxygen generators in all aircraft lavatories be rendered safe. Operators could either remove the oxygen canisters or activate them to produce oxygen until the chemical reaction was complete; the exhausted canisters could be left in place.

Since the oxygen canisters were placed in lavatories, as they are above all passenger seats, for safety reasons, the initiative and the secrecy surrounding these canisters apparently have a security aspect. Terrorists apparently could use the canisters in the lavatories as an “accelerant” in assembling a bomb or they could simply ignite the canister and let its heat – a byproduct of producing oxygen – create whatever scorching damage is possible.

This security – not safety – action can be interpreted in one of two ways: 1) someone awakened to a problem that is greater than publicly suggested, or 2) a credible warning has been received that terrorists are “on to” the possible use of these oxygen generators as a way to commit mayhem on the airplane without having to worry about getting contraband through airport security.

Exactly how much mischief is possible with one oxygen canister in the lavatory is problematic. In 1983, an Air Canada DC-9 operating as flight 797 made an emergency landing at Cincinnati with a fire later found to have begun by burning cigarette ashes in a lavatory trash bin. Twenty-three of the 46 people on board were killed. This accident was the impetus for installing fire suppression in the lavatories. There is no publicly available technical report on the probability of a lavatory fire extinguishing system being overwhelmed by an oxygen-fed trash bin fire.

Air Canada Flight 797 burns on the runway

This scenario is weak justification for removing the oxygen generating capability from the lavatory. The problem is that this notice and the accompanying AD state nothing as to why the oxygen canisters pose a dangerous threat. Just saying so is hardly convincing. As will be shown below, the FAA Technical Center reports do not support the notion that oxygen generators installed in the lavatory constitute a unique threat.

On one hand, the FAA is acting on a presumed security threat, while on the other hand the agency is placing at risk every passenger caught in the lavatory during decompression. If the cabin decompresses at 30,000 feet, the normal human time of useful consciousness is between 1 and 2 minutes. This time is defined as the interval in which the effects of hypoxia must be recognized and emergency oxygen supplied while the airplane quickly descends to 10,000 feet, where adequate oxygen exists without pressurization. Since the average passenger is not likely to recognize the effects of hypoxia if caught in a locked lavatory with no emergency oxygen, death is almost sure to result.

On 8 March, the FAA published a notice in the Federal Register, inviting the public to comment on the action by 22 April. The notice is full of euphemisms which a person reading it would be hard-pressed to divine what is going on, and why.

The notice publishes the airworthiness directive (AD) previously sent by “individual notices” to the airlines. AD 2011-04-09, effective 14 March 2011, requires all chemical oxygen generators in the lavatories to be activated until expended or removed from the lavatory within 21 days. While not stated, a deadline of 4 April is implied, so no doubt airline maintenance activity is being carried out as of this writing.

The finality of the FAA’s action is apparent from the AD, which states, “After the effective date of this AD, no person may install a chemical oxygen generator in any lavatory on any affected airplane.”

Affected airplanes involve 6,000 airliners in U.S. register. This fact cannot be gleaned from the FAA’s 8 March notice, although in all other such notices the number of aircraft and the cost of corrective action are provided. In this case, one can look up the FAA’s “Regulatory Evaluation” to know that at $170 per airplane, the cost of the de-activation program is placed at $1,020,000.

No cost-benefit is provided, as in the cost of an averted terrorist attack, nor is the cost of a passenger death provided in the event of decompression while in the lavatory. The statistical value of a human life is approximately $3 million.

A brief explanation of oxygen canisters is in order. About the size of a soda pop can, the steel containers are packed with sodium chlorate. When ignited by a percussion cap, the core chemical will burn for about 15 minutes, producing oxygen. The oxygen is routed via a tube to a face mask, providing the user with a means to remain conscious while the pilot rapidly descends the aircraft to 10,000 feet. At this altitude, there is sufficient ambient oxygen for the passengers.

All canisters – above the passenger seats and in the lavatories – are activated from the cockpit.

In the May 1996 crash of ValuJet flight 592, a DC-9, the National Transportation Safety Board (NTSB) determined that a shipment of burning canisters in the forward belly hold caused the loss of the aircraft. According to the NTSB, a canister ignited which in turn ignited other canisters, and the resulting conflagration burned out of control, causing the stricken airplane to crash into the Florida Everglades shortly after takeoff from Miami. All 110 people aboard were killed. The accident prompted the FAA to order all belly holds to be equipped with fire detection and suppression equipment (the fire liner having clearly failed to contain the blaze until a safe landing could be made).

It was never clear from the NTSB investigation how the fire started. The FAA Technical Center in Atlantic City, NJ, did some tests for the NTSB by placing canisters and their packing material in a test chamber and starting a blaze by yanking on a piano wire attached to the percussion cap of one canister. The possibility of an electrical fire was never seriously explored, or the chance that a protective cover on a canister packed for shipment was dislodged during loading onto the flight. It was never satisfactorily explained how the ValuJet fire actually started.

The Technical Center produced a report in May 1999 which concluded:

“The activation of an aircraft oxygen generator canister produced surface temperatures above 400º F [410º to be precise]. Tests conducted in this report [and cited in the NTSB’s ValuJet report] demonstrate that a generator activated in a confined space may ignite adjacent combustible material due to the hot surface and elevated oxygen concentration. This was shown with cylindrical cardboard shipping containers with urethane foam pads and with cardboard boxes with bubble plastic shipping material. An addition, the initial fire involving burning combustible material will cause additional generators to activate, creating an intense fire associated with burning in an oxygen-enriched environment and reach temperatures above 2,700º F.”

The report stated that the skin temperature on one ignited canister never exceeded 400º F.

Test results after 3 thermocouples were held against the surface of a single Scott oxygen generator -- not hot enough to ignite cardboard or paper

When three canisters were placed inside a tin can and ignited, then the temperature reached the 2,000º F+ range. There is nil possibility of such an arrangement for installed canisters.

Three generators placed inside a tin can

Would terrorists board with a tin can of the requisite size? There are other important caveats. The report states the outlet tubes and overpressure relief valves on the generators were sealed to force the canisters into a resulting rupture; it was through rupturing that the hot burning chemical therein ignited nearby materials. One might suggest this wasn’t a “real world” test, as the canisters were sabotaged to ensure a rupture and thus towards increased “fire” results. Even at that, fire resulted in only 4 of 7 trials. The conclusion of this Technical Report is not supported by its details.

Is the action to remove or render unusable the lavatory generators based on activation in a “confined space” with “adjacent combustible material”? There is no cardboard or bubble wrap located anywhere near canisters in their normal overhead locations. As for confined space, every canister is installed in a restricted area. It also takes more than one burning canister to really heat up the temperature sufficiently to ignite adjacent material.

An April 2003 Technical Center report concluded that a minimum temperature of 600º F would be needed to cause sympathetic eruption of flames in an adjacent canister. Given the uncertainties regarding designs not tested, the report concluded that generators should not be exposed to temperatures above 400º F.

Outwardly bulged generator (top) compared to a normal generator (bottom)

There is one scenario that poses a hazard: a burning, ruptured canister in the overhead of the lavatory igniting adjacent Mylar insulation. Through AD 2008-23-09 (issued three years ago), the FAA has mandated that removal of this material be accomplished by 2016. Here is an “identified safety risk” with legs. However, the lack of urgency in AD 2008-23-09’s time for compliance is more typical of the FAA’s approach to not unduly inconvenience the airlines. Moreover, the area of risk extends to all Mylar in the overhead, not just that portion over the lavatories.

To conclude, the oxygen generators might be getting an undeserved bad rap. Some overly complicated terrorism scenarios have to be served up to justify this action. A book of matches and some smuggled lighter fluid seem more dangerous than rigged oxygen canisters.

Given the results of the Technical Center flammability trials, the possible value of a lone oxygen generator used as a terrorist weapon seems problematic. The secretive, hasty action by the FAA seems out of proportion to the remote and possible use of a canister by terrorists.

An FAA spokeswoman said that during the past 10 years there have been only 12 incidents of pressure loss at cruise altitude and none in which the cabin altitude reached an unsafe level for breathing. However, a survey of incidents in which oxygen masks were deployed found 115 such events from March 2001 to 11 March 2011. When the oxygen masks drop from their compartments under the overhead bins, the oxygen canisters have been activated.

As for the safety of innocent passengers caught in the lavatory, the notice says the pilot-in-command (PIC) will “brief the crew that in the event of a rapid decompression the lavatories need to be checked.” Remember, the lavatory doors are locked from the inside. Given time of useful consciousness, the passenger inside the lavatory likely will be out cold, slumped over and heading towards an hypoxic death while the flight attendant attempts to unlock the door. In many cases the unlucky occupant will be later found (at best) insensible, but more likely deceased if aged and infirm.

Once the passengers hear of this action in new pre-flight safety briefings, the FAA may rue this action to remove emergency oxygen from the lavatories. When the first passenger gets hospitalized, or worse, because of a lack of oxygen in a depressurization event, the plaintiffs’ lawyers will have a field day.

It is not known if the Europeans will go along with the FAA’s plans.

As for the terrorists, has all the publicity surrounding this action alerted them to the notional possibilities?

If a type of device known as a pressure swing adsorption (PSA) oxygen generator been considered, a suitable substitute for airplane lavatories (i.e., not a flame accelerant) could be fitted.

The FAA announced that public comments are due by 22 April.

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