One day before the 12th anniversary of the crash of TWA Flight 800 off Long Island, the federal government Wednesday announced a new rule it said would eliminate the risk of exploding fuel tanks on jumbo jets.

The rule, which will be in effect as early as next week, requires that inert gas be injected into empty center fuel tanks to prevent the remaining vapor from exploding.

The National Transportation Safety Board determined that vapor in the center tank of Flight 800 had been ignited by exposed wiring, blowing the plane apart in t he air south of Mastic Beach, killing all 230 people on board as the jumbo jet headed for Paris.

Secretary of Transportation Mary Peters said manufacturers will have two years to install the devices on new jets. The government is giving airlines nine years to add the devices to 2,730 Airbus and Boeing large jets built since 1991 that are still flying.

"Today we are raising the bar on aviation safety," NTSB chairman Mark Rosenker said. "We believe this will save lives."

The announcement was made at an Ashburn, Va., facility that contains the partially reconstructed Boeing 747 destroyed in the explosion shortly after takeoff from Kennedy Airport on July 17, 1996. Peters pointed out that wreckage has been reassembled as a teaching tool and the facility is dedicated to the crash victims and their families.

"The new rule is designed to prevent the risk of catastrophic explosion," Peters said, adding it is "a known risk on large passenger planes." She said three fatal accidents involving center fuel tanks have occurred in the last 18 years.

Families of crash victims have pushed for the change and some of them have been critical of the Federal Aviation Administration for taking too long to remove the flammability risk.

"I'm certainly glad that it has become a rule," said James Hurd of Severn, Md., who lost his son Jamie in the accident.

"On the other side, I'm disappointed it took so look to do it," said Hurd, who serves as vice president and director=2 0of the Families of TWA Flight 800 Association and was a member of the FAA committee that developed safety upgrades. "I realize the bureaucracy needs to go through its process. But I feel it should have been done within five to six years."

Acting FAA Administrator Robert Sturgill said that as soon as the NTSB identified the fuel tank as the likely cause of the Flight 800 explosion, "we began working on a solution so no other family would have to be standing on a beach." He was referring to the families of Flight 800 passengers and crew who gathered at Smith Point County Park near the site of the crash 12 years ago and every anniversary since.

Sturgill said the FAA move quickly to make initial changes, issuing more than 150 directives on improving the wiring to reduce the ignition risk. "But we still had the flammability issue" until Wednesday, he said.

Peters said the FAA has already taken steps to remove the threat of explosions from exposed wiring but full safety in the air required dealing with the explosive vapors in empty tanks as well. She said the FAA in 2002, with help from the industry, had developed a device for making the gas tanks inert by injecting nonflammable gases such as nitrogen.

She noted Boeing, the manufacturer of the jet designated as TWA Flight 800, developed its own system and began installing it several years ago on new planes.

"I recognize that this is a very critical time for commercial aviation" with soaring fuel prices crea ting upheaval in the industry, Peters said. But she said the industry could not afford to have another crash caused by a fuel tank.

Peters said the cost of installing the new devices would range from $92,000 to $311,000 per aircraft, depending on its size. She said this cost represented as little as one-tenth of one percent of the cost of a new aircraft.

The American aircraft that will be required to be retrofitted include approximately 2,730 aircraft. They are 900 Airbus A320s and 50 A330s as well as 965 Boeing 737s, 60 Boeing 747s, 475 Boeing 757s, 150 Boeing 767s and 130 Boeing 777s all built since 1991.

In 2005, the FAA proposed a plan to retrofit more than 3,000 jetliners with a fuel tank safety device. But airlines balked at the idea, citing the massive cost of the retrofit.

Fuel tank explosions have been linked to the destruction of four jetliners -- all Boeing aircraft -- since 1989. Among them were an Avianca 727 in 1989; a Philippine Airways 737 in 1990; and a Thai Airways International 737 in 2001.

In a news release, Sen. Charles Schumer (D-N.Y.) praised Wednesday's announcement.

"This plan will go a long way toward preventing another terrible tragedy like TWA Flight 800 from ever happening again," Schumer said. "But the proof in the pudding is in the eating, and the administration now must provide the resources to ensure these improvements are made as quickly as possible. Air travelers shouldn't have to wait another decade to fly safely."< br>
Staff writer John Valenti contributed to this story.