WASHINGTON » A hearing into a record-setting safety recall of deadly, defective vehicle air bags saw members of Congress complain Tuesday that it has taken too long to launch and that dire questions remain as to how quickly air bags inflators can and will be replaced.

“Six months ago I asked the question: What should I say to the mom in Michigan who asks me if she and her family are safe behind the wheel?” asked Rep. Fred Upton, R-Mich., who chairs the House Energy and Commerce Committee. “Six months later … I have to ask the same question.”

Tuesday’s hearing before the Commerce, Manufacturing and Trade Subcommittee — which is part of the Energy and Commerce Committee — comes less than two weeks after federal regulators and the air bag maker, Takata, announced it was doubling its recall to cover some 34 million vehicles nationwide.

Six deaths and more than 100 injuries have already been linked to defective air bag inflators which in some cases have ruptured, spraying shrapnel at drivers and passengers in certain vehicles. While regulators with the National Highway Traffic Safety Administration and Takata have been in talks for months, if not years, it was only last month when the air bag manufacturer publicly acknowledged the defect.

In December, the Commerce, Manufacturing and Trade Subcommittee held its last hearing on the Takata air bag recall, which then was limited to certain humid regions of the country and covered about half as many vehicles.

But even with the new, wider recall, affecting models of 11 auto manufacturers, subcommittee Chairman Michael Burgess, R-Texas, said it “isn’t clear … why we are launching this national recall now instead of almost a year ago when we had almost the same information.”

In the interim, said Burgess, another death, one in his home state, occurred.

“Every morning I fear I am playing headline roulette waiting for another rupture,” he said. “While it has now been confirmed that there is a defect affecting … Takata air bag inflators, we still don’t have any great clarity about what was the root cause and how we know that we are safe going forward.”

NHTSA head Mark Rosekind, Takata Executive Vice President Kevin Kennedy and officials of industry groups testified at Tuesday’s hearing, with the air bag manufacturer expressing “regret” for the deaths and injuries and saying the company was moving on nationwide recalls of certain inflators even though the rate of ruptures was tiny.

“It is unacceptable to us and incompatible with our safety mission for even one of our products to fail to perform as intended and to put people at risk,” said Kennedy, who said all driver side inflators and one of the passenger side inflators using so-called “batwing” shaped propellant wafers are being recalled nationwide.

But Kennedy faced several questions about the use of ammonium nitrate as a propellant, which has been blamed by some for the ruptures. Acknowledging that it was one of several factors involved, Kennedy said the company still plans to use the material in some of its inflators — though with a moisture-reducing agent the company says eliminates the risk of rupture.

Age, high-heat conditions and high-humidity have been blamed as likely reasons for the ruptures, Rosekind and Kennedy said, though no ultimate “root cause” has been determined. About half of the replacement air bag kits are expected to not contain ammonium nitrate at all, Kennedy added.

When Burgess asked about the use of ammonium nitrate and its safety, Kennedy said part of the problem of determining a root cause of the ruptures is that, “You can put two inflators in that situation (and) one is fine and one is not.”

“You’re not providing me much reassurance with that answer,” Burgess responded.

Kennedy said about 750,000 replacement inflators were shipped in May. He expects that number to increase to about 1 million a month soon. By the end of the year he said he expects 70 percent of those replacements to be made by Takata’s competitors. He acknowledged that more testing of inflators — including those shipped as replacement parts — will continue to make sure they are safe.

Several Democrats on the panel, meanwhile, used the hearing as a call to pass new legislation giving regulators more authority to order recalls and forcing automakers and suppliers to share more information with the public.

Questioned about the need for such legislation and more funding for personnel by Rep. Jan Schakowsky, D-Ill., Rosekind acknowledged that any legislation which increases the maximum fine from the current $35 million cap to $300 million or more would be welcomed, as would more agency staff.

“At some point you need people and authority to get the job done and that’s a concern,” Roskeind said. Republicans in the House, however, have so far balked at giving the Obama administration what it has asked for, including a budget request to nearly triple NHTSA’s defect investigations office.

Burgess suggested he would consider taking a request for more funding to House appropriators if Rosekind would provide him a detailed spending plan.

While the recall is the largest safety campaign ever ordered in U.S. history, Upton — who said he had his own close call in an accident two weeks ago when he hit two deer and his air bags deployed — said that eye-opening number isn’t enough to ensure the public safety, since it is not known when the replacement parts will be ready and whether they will absolutely be effective. Even NHTSA has acknowledged that already replaced parts may have to be replaced again as it researches their safety.

Upton said he was concerned that NHTSA and Takata “decided to release head turning, headline-grabbing recall numbers at a time when the information is not yet actionable for consumers.”

“Drivers read about the biggest recall in history but could not look up if their car was part of the recall. How does that help safety?” asked Upton.

Rosekind said drivers, however, should be able to check vehicle identification numbers at safercar.gov and should check regularly — every week — to see whether their vehicles are part of this recall effort. It could take two weeks or more to have all the VINs included in the safercar.gov site, he added.

Rosekind, in his testimony, made it clear, however, that NHTSA will continue its research to make sure that replacement parts are safe and said drivers should repeatedly check to see if their cars are part of a recall — even if they have been recalled previously.

As to when the recall would be complete, Rosekind — who has previously said it could take years — said there is no way at this point to know but he hopes to be able to provide much more information on a timetable after a public meeting with automakers and suppliers by fall.

“If anybody gave you a number (as to how long it will take),” he told Upton, “they don’t know what they’re talking about.”