For more than a decade, the Japanese company Takata, one of the largest suppliers of airbags, denied that its products were defective even as motorists were killed by exploding airbags and automakers around the world recalled millions of cars equipped with its products.
But on Tuesday, in an about-face, Takata admitted that its airbags were defective and agreed to double the number of vehicles recalled in the United States, to nearly 34 million — or about one in seven of the more than 250 million vehicles on American roads — making it the largest automotive recall in American history. The airbags can explode violently when they deploy, sending shrapnel flying into a car’s passenger compartment. Six deaths and more than 100 injuries have been linked to the flaw.
“Up until now Takata has refused to acknowledge that their airbags are defective,” said Anthony Foxx, the transportation secretary. “That changes today.”
The announcement also indicated a shift for the National Highway Traffic Safety Administration, which for years had been criticized by lawmakers and safety advocates as being too lax on the industry it oversees. At one point, in 2009, the agency opened an investigation into Takata and its airbags, only to close it six months later, citing “insufficient evidence.”
But since the appointment of a new administrator, Mark R. Rosekind, the agency has shown greater assertiveness toward companies like Takata.
“From the very beginning, our goal has been simple: a safe airbag in every vehicle,” Mr. Rosekind said. “The steps we’re taking today represent significant progress toward that goal.”
Takata, in a statement, said that the announcement was the culmination of a year of work with automakers and the safety agency.
“We are committed to continuing to work closely with N.H.T.S.A. and our automaker customers to do everything we can to advance the safety of drivers,” said Shigehisa Takada, Takata’s chairman and chief executive.
Despite the sweeping nature of the announcement, the agency said it would not know exactly which models of cars would be recalled until it coordinated with automakers, which could be several days. The final number may change as more tests are performed, Mr. Rosekind said. Ten automakers, including Honda, Chrysler and Nissan, have recalled cars in the United States because of the defect.
Mr. Rosekind acknowledged that the repairs could take several years to complete, but he said that consumers could still drive their cars in the meantime.
“Yes, people need to drive their cars,” Mr. Rosekind said, adding that they should be checking with their dealers often to make sure the defective airbags were “replaced as soon as possible.”
Honda, the automaker that has been most affected by the Takata airbag recalls, said that it was reviewing the announcement to determine what fresh recall measures might be required. Honda already said that it was looking to other suppliers to provide replacement airbags.
Nissan, Chrysler, Toyota and BMW also said they needed to review the announcement before taking any further action. None of the automakers would say whether they expected to have access to enough replacement parts to repair all the cars potentially carrying defective airbags.
Officials at other affected automakers, including Ford, did not immediately respond to requests for comment. Even now, Takata and automakers continue to search for the root cause of the defect. But in new filings with the safety agency, Takata went beyond its previous statements that there had been some errors in manufacturing and admitted to flaws in the airbags’ design and components.
For example, Takata said that the propellant in the inflaters — the explosive material that generates the gases to inflate the airbag — could degrade over time if exposed to high humidity and changes in temperature, making it prone to “overaggressive combustion.”
Former Takata engineers told The New York Times last year that they had raised concerns over a decade ago that ammonium nitrate, the explosive material Takata uses, was sensitive to moisture and temperature swings. But those concerns went unheeded, they said.
And for the first time, Takata also acknowledged that its testing had uncovered leaks in some of its inflaters that could allow moisture to seep into them over time. When that happens, the propellant breaks down, making it more susceptible to exploding violently.
Last week, a former Takata consultant said that tests he carried out on prototype Takata airbags in the early 2000s revealed leaks, and that he had urged the company to use a different leak testing method, one that he had devised and was offering to sell to the company. His advice also went unheeded, he said.
But in a statement on Tuesday, Takata argued that under industry-mandated testing, it could not have been expected to spot such complex problems.
“The potential for this long-term phenomenon to occur was not within the scope of the testing specifications prescribed by the vehicle manufacturers,” the supplier said in a statement.
In the face of mounting evidence, federal safety regulators in February began to fine Takata $14,000 a day because it had not cooperated fully in the agency’s investigation. The company disputed the agency’s assertions. With the expansion of the recall, though, regulators said they would suspend that fine, which had reached more than $1 million. It is unclear if it will be collected.
Takata’s airbag problems date back almost 15 years. As early as 2000, customers filed complaints with the National Highway Traffic Safety Administration alluding to rupturing airbags in models that contained Takata products.
Gradually, awareness grew within the company. The New York Times reported last November that Takata had ordered tests on the airbags in 2004 and found signs of defects, but did not report the results to regulators. Takata has disputed the report.
In November 2008, Honda recalled more than 4,000 cars with Takata airbags and then, six months later, after a teenager was killed by fragments from an exploding airbag, the company recalled an additional 510,000 vehicles.
As the number of cars under recall continued to expand, the safety agency started a second investigation into the airbags last June and, late last year, began to demand that automakers issue nationwide recalls in the United States.
Last week, Honda, Toyota and Nissan expanded their worldwide recall by 11.5 million cars.
Tuesday’s announcement drew praise from some lawmakers who have been critics of Takata. “Folks shouldn’t have to drive around wondering if their airbag is going to explode in their face or if their car is going to be on another recall list,” said Senator Bill Nelson of Florida, the top Democrat on the Senate Commerce Committee and a central figure in a congressional investigation into the defective airbags. “Let’s hope Takata’s admissions today tells us the whole story.”
But at least one victim is not applauding the announcement.
“I’d like to know why it took them till now,” said Corey Burdick, a 26-year-old from Eustis, Fla., who was blinded in one eye last year when a piece of metal shot out of the Takata airbag in his 2001 Honda Civic. “What’s different now from a year ago?”
Mr. Burdick, who supports a wife and two young sons, works in a warehouse loading pallets with a forklift. He has filed suit against Takata and Honda.
“It’s been a mix of emotions, like a roller coaster,” he said. “It’s depressing because this could happen to someone else.”