A probe into whether an exploding oxygen cylinder may have ripped a hole in a Qantas Airways Ltd. jet last Friday brought to mind a deadly crash 12 years ago when oxygen canisters ignited a fire that caused a ValuJet DC-9 to plunge into the Everglades.

Federal Aviation Administration spokesman Les Dorr cautioned, however, that the only thing the Qantas mishap and the ValuJet crash in 1996 "have in common is the word oxygen."

The high-pressure oxygen cylinders at issue on the Qantas aircraft that plummeted from 29,000 feet over the South China Sea before landing safely in Manila were "totally different equipment" from the mislabeled and improperly packed oxygen canisters shipped as cargo on ValuJet Flight 592.

"There's no link at all between the two," Dorr said.

The theory that missing cylinder No. 4 may have blown a six-foot hole through the Qantas Boeing 747 carrying 365 people was supported by the discovery of a valve and handle fragments in the passenger compartment, near where the missing cylinder was stored, the Australian Transport and Safety Bureau said yesterday.

But aviation consultant Robert W. Mann, of R.W. Mann Associates, of Port Washington, N.Y., said the Qantas and ValuJet incidents, "other than the common word oxygen, are completely unrelated."

The chemical oxygen generators that ignited a fire in the cargo compartment of ValuJet 592 on May 11, 1996, were incorrectly packed and improperly shipped by ValuJet's maintenance contractor, in violation of FAA rules forbidding hazardous material in aircraft cargo holds, Mann said.

The chemical oxygen canisters, which when activated produce oxygen, did not have safety devices on them and were not labeled hazardous material. The cargo manifest said the canisters were empty, when they were not. All 110 people on board died.

The Qantas jet "was a completely different story," Mann said. Qantas Flight 30 was carrying emergency oxygen cylinders, designed for cockpit use, and used on routes where it is not possible to descend below 10,000 feet above sea level without running into a mountain range, Mann said.

The cylinders, such as Qantas was carrying, are not widely installed, Mann said. They are found in aircraft that fly in mountainous regions, such as the Himalayas, Nepal and Tibet.

"No aircraft flying in the U.S. requires a system" such as Qantas had, Mann said.

Oxygen systems on airplanes have generally not been controversial. "You don't normally hear of them just blowing up," said the FAA's Dorr.

After the ValuJet crash, the U.S. Department of Transportation imposed an emergency ban on the shipment of oxygen canisters. (ValuJet never recovered from the crash and in 1997 merged with AirTran Holdings Inc. and took AirTran's name.)

The FAA directed U.S. airlines in 2006 to inspect oxygen cylinders' support brackets on Boeing 747-400 planes because they may not have been properly heat-treated, which the FAA said could lead to oxygen leaks and fire hazards.

In April 2008, the FAA extended the directive to foreign carriers to check the brackets on certain Boeing aircraft. Qantas said only three of its aircraft were affected and each was inspected and brackets were replaced.

Investigators from Australia, the United States and Boeing have not ruled out that the aircraft had a structural problem. "It's far too early to speculate," Dorr said. Australian investigators are handling the probe, assisted by the National Transportation Safety Board, the FAA and Boeing.

Contact staff writer Linda Loyd at 215-854-2831 or lloyd@phillynews.com.