The pilots were forced to drop altitude rapidly
An exploding oxygen cylinder probably caused the hole that appeared in a Qantas jet during a flight, a safety official has confirmed.
Julian Walsh, of the Australian Transport Safety Bureau, said it appeared parts of the tank had exploded through the passenger cabin floor.
The plane, which was flying from London to Melbourne, was forced to land in the Philippines on Friday.
Passengers reported a loud bang and then rapid decompression of the cabin.
Pilots were forced to descend rapidly by almost 20,000ft (6,100m), but none of the 365 passengers and crew was hurt in the incident.
"The ATSB can confirm that it appears that part of an oxygen cylinder and valve entered the passenger cabin," Mr Walsh told reporters.
He said shrapnel from the tank sheared off part of a door handle, but added that the design of the door prevented it from opening in mid-air.
A full search of the plane has yielded no trace of the missing cylinder, leading officials to conclude that it probably exited the plane through the fuselage.
WHY QF30 DESCENDED 20,000FT
Planes are pressurised as cruising altitudes are freezing and lack sufficient oxygen to breathe
Hole causes decompression, rapidly reducing air pressure and risking exposure
Oxygen masks are deployed and pilot makes emergency descent to breathable altitude
Qantas has been told to inspect every cylinder on its Boeing 747 fleet.
Investigators have been poring over the plane's equipment to find an explanation for the hole.
On Tuesday they announced that the in-flight voice recorder had been examined, but yielded no clues because it was wiped during the incident.
"The oldest recording on the cockpit voice recorder commenced after the descent and diversion to Manila," lead investigator Neville Blyth said.
He added that the flight-data recorder, which normally contains 25 hours of information, was still being examined.
A preliminary report on the findings should be released in two to three months.