Usage History
Remarkably, for a widely-deployed piece of safety equipment, some research has suggested that no lives are known to have been saved by use of an emergency oxygen mask — nor any lives lost through the absence of one — while carrying oxygen generating apparatus, albeit as cargo, has caused at least one fatal accident (ValuJet Flight 592), in 1996, where expired chemical oxygen generators were loaded as cargo on board the aircraft without being safely deactivated; in transit, it is believed these generators activated; the heat generated from the activated generators caused the boxes in which they were improperly stored to catch fire.
In the three cases of in-flight explosive decompression studied, one took place at a sufficiently low altitude for atmospheric oxygen to be sufficient, while in the other two cases the systems failed in the accident and did not provide oxygen to the passengers. However, in several other cases, oxygen masks have kept passengers conscious and alert during a decompression and have protected passengers from injury.
The cockpits of aircraft generally contain a separate oxygen system for the flight crew, and effective use of these has no doubt saved many aircraft. Hypoxia, which can cause severe disorientation and unconsciousness, sets in quickly; if a flight crew does not realise the cabin has decompressed, or is too slow to respond, they can quickly lose control of the aircraft. For example, on Helios Airways Flight 522 in 2005, the cabin depressurized slowly during the ascent to cruising altitude, and while the passenger oxygen masks were released at 14,000 feet, the crew were disoriented and failed to realise the significance of this; they lost control within a few minutes, having not put on their own oxygen masks. In the 1999 South Dakota Learjet crash, the NTSB report concluded that only a few seconds delay in using their masks following decompression would be enough to incapacitate a flight crew.
In one case, in 2000, a Boeing 737-800 suffered a slow depressurization, coupled with the failure of the cabin altitude warning system. The depressurization was only discovered by the crew due to the automatic deployment of the passenger oxygen masks; this gave them time to respond appropriately.
In 2011, the FAA announced that it had ordered the removal of all oxygen masks from airplane lavatories in the United States for security reasons.
Read more about this topic: Emergency Oxygen System
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