There is no evidence of there being a systematic safety problem with aircraft oxygen bottles, says Australian investigators. The findings are published in their latest report into a July 2008 accident in which an oxygen bottle on a Qantas Airways Boeing 747-400 exploded.
The Australian Transport Safety Bureau's second interim report on this accident says that to date there is no evidence of systematic problems with oxygen bottles of this type.
On 25 July 2008 the Qantas 747 (VH-OJK) was cruising at 29,000ft (8,850m) en route from Hong Kong to Melbourne when one of 94 oxygen cylinders on board exploded, causing a rupture of the forward fuselage and depressurisation of the cabin.
The rupture was about 2m along the length of the aircraft and 1.5m vertically.
ATSB says the cylinder that exploded was lost but, for the purposes of its investigation, it has obtained five cylinders from the same manufacturing lot.
It says all the pressure tests of the cylinders met or exceeded safety specifications.
"The minimum allowable rupture pressure prescribed ....was 4,111lb/in2 [284bar] and all the test cylinders exceeded that value", it says.
The report also provides details on how the cabin crew and cabin equipment responded to the depressurisation of the cabin, saying: "The passenger address tape reproducer - the automatically activated system for addressing passengers in the event of a depressurisation - did not function."
It adds that "not all the oxygen masks deployed and as a result two passengers did not immediately start using oxygen and displayed symptoms of hypobaric hypoxia", a condition resulting from oxygen deprivation.
The safety bureau says Qantas has since taken action to address these cabin issues.
As for why one of the aircraft's oxygen cylinders exploded, the bureau says it will complete its investigation early next year.