Removal of Lavatory Oxygen Shrouded in Speculation

Mon, Apr 25, 2011 — David Evans


The order to remove emergency oxygen from lavatories of transport-category airplanes is a done deal, but the Federal Aviation Administration (FAA) did indicate that public comments would be accepted on the matter. (See Aviation Safety Journal, March 2011, “Emergency Oxygen Ordered Removed From Lavatories” and “ ‘Huge Favor’ To Airlines Ordering Emergency Oxygen Removed From Lavatories”)

The public has responded. Comments filed in the docket reflect both common sense and more than a few questions about the rationale behind the FAA’s peremptory action. Below, four comments:

From Scot Thompson:

“As usual the FAA has written an AD [airworthiness directive] as clear as mud. Under the Unsafe Condition paragraph (e) it is stated ‘that the current design of chemical oxygen generators in the lavatories presents a hazard …’ The oxygen generators … are the same in the cabin as well as the lavatories, so why are the cabin oxygen generators not a ‘hazard’? In the Parts Installation paragraph (i) it is stated ‘no person may install a chemical oxygen generator in any lavatory on any affected airplane’. This appears to contradict paragraph (e) and leads one to believe there is a problem with the design of the lavatory oxygen system, not the generator in and of itself. Why is this now an issue?”

From Robert Montgomery:

“The proper use of oxygen masks is fundamental to passenger and crew safety during any cabin depressurization at altitude, loss of cabin pressurization control or monitoring capability, or circumstance involving smoke, fire or fumes in the cockpit or cabin area. The removal of these generators, unless a suitable replacement is installed, represents a substantial hazard to whoever occupies the lavatory.

“Consequently, it is incumbent on the FAA to modify the Airworthiness Directive in question to include language requiring operators to either make the lavatories inaccessible to passengers or to provide an alternative means of oxygen supply to the lavatory.

“Because the FAA fails to adequately justify the ‘hazard’, it is not possible to properly evaluate whether or not the AD is reasonable and proportional. Consequently, to meet its statutory requirements, the FAA needs to reissue this notice with a description of the hazard and extend the comment period.”

From Chandran Madhavan, Flight Safety Department, Air India:

“Reference to the above AD, I wish to know:

1) How is the safety of a passenger ensured if an explosive decompression takes place when he is in the toilet where an oxygen generator is removed as per the above AD?

2) What is the crew action if a passenger is in the toilet when the decompression takes place after the implementation of this AD?

3) There is no mention of any alternative method to ensure safety of a passenger in toilet in the event of an explosive decompression after the implementation of the above AD.

4) How is the oxygen supply made available to passenger in toilet post this AD?”

From John King:

“Dear Sirs:

“With the April 1st depressurization incident of Southwest flight 812, I have noted with great concern the stories of incapacitation of the front cabin flight attendant and a number of passengers in what appears to be under 30 seconds. This [seems] to undermine the assurances given with the FAA’s public announcement of this AD that ample time would allow for all to gain access to the oxygen masks and that flight attendants would escort any in the lavatories to their seats where oxygen would then be available.

“More importantly, while following the reports of this AD, there were numerous references to the NTSB’s Final Report and probable cause to the loss of ValuJet flight 592 (NTSB/AAR-97-06) as somehow a cautionary tale to the dangers of oxygen generators and they played a pivotal role in that loss. In the NTSB’s ‘Probable Cause’ and ‘Findings’, it was asserted that an initial oxygen generator became hot enough to ignite adjacent flammable packing materials and that the oxygen produced was enough to overwhelm the fire retardant design features of that sealed Class D cargo compartment. There are many questions and contradictions within that Report but for here I’ll address just two assertions that may be possibly relevant to this AD and how they are rendered speculative and contradictory by specific documents from the FAA’s Hughes Technical Center in New Jersey.

Assertion 1. The generator oxygen produced is sufficient to aggressively propagate a fire.

“Contradicting this is the FAA Tech Center May 4, 1994 letter to the Danish AAIB [Air Accident Investigation Board] Report 2/96. On November 24, 1993, SAS MD-87, Registration SE-DIB, incurred a severe fire over the right rear lavatory. Because O2 generators were consumed, the AAIB asked the FAA’s Hughes Tech Center to test these for any possible effects on that fire … From that Tech Center letter response, this AAIB report concluded that:

‘Based on these tests, it was concluded that the involvement of a discharged oxygen generator had minimal effect on the SAS MD-87 fire…’

Of the Tech Center tests, the Tech Center letter…said:

‘Two tests were conducted using solid oxygen generators. The first tests utilized a generator mounted above a pan of jet fuel fire. Over-heating from the fuel fire caused the generator to activate. Intensification of the fuel fire was limited to the immediate area of the discharging oxygen. In the second test the oxygen generator was placed in a cardboard box containing shredded paper. After the box was ignited and burned for a period of time, the generator activated due to the surrounding fire. Again, intensification of the fire was contained to a small local hot spot. Based on these tests, it was concluded the involvement of a discharged oxygen generator had minimal effect on the SAS MD-87 fire.’

Assertion 2. Exterior heat from a discharging oxygen generator will ignite adjacent packing materials.

“Contradicting this is the Tech Center Report DOT/FAA/AR-TN99/9 … May 1999, Activation of Oxygen Generators in Proximity to Combustible Materials … Regarding the exterior (shell) temperature of operating oxygen generators, quote:

‘Test 16 > Scott P/N 801386-83 on thermocouple fixture, pulled pin, max shell temperature 250 F in 8 mins…

‘Test 19 > Puritan P/N 117003-14 on thermocouple fixture, pulled pin, max shell temp 250 F’

“It is important to note here with all of the above tests that both the oxygen output tube and the overpressure relief valve were blocked and thus the oxygen generators were allowed to rupture. In all cases, it did not. Whether or not a potential terrorist would have the necessary knowledge and tools to do the same to a generator secured in place and surrounded by other structures can only be left to the imagination.

“The industry recognized and accepted auto ignition temperatures for common packing materials (paper, plastic wrap) … of 450 degrees F.

“Based upon these two Tech Center documents, it is inconceivable that oxygen generators have any potential as a terrorist device, or to endanger an aircraft … on the flip side, the FAA did not disclose just how an oxygen generator may be refashioned into a dangerous device. I seek your assurances that nothing mentioned above has had any weight in your decision to take the proven risks of oxygen deprivation to the flying public.”


Based on these submissions to the docket, two questions pertain:

1. How will emergency oxygen be provided to someone in the lavatory when a decompression occurs? This publication has suggested an alternative that could not, under any circumstances be utilized by terrorists. (See Aviation Safety Journal, March 2011, “Emergency Oxygen Need Not Come From A Chemical Canister”)

2. How are lavatory O2 generators a hazard to continued safe flight when the Tech Center reports document that they do not get hot enough to ignite adjacent materials?

As of this writing, based on a sample of six airline flights, pre-flight safety announcements are not including a caution to the effect that no emergency oxygen is available in the lavatories.

The reason behind the AD remains shrouded in mystery and speculation, and its ostensible purpose is contradicted by reports from the FAA’s own Technical Center.

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