One of the largest auto industry recalls is about to double in size, and then some. The National Highway Traffic Safety Administration (NHTSA) has expanded the recall of Takata airbag inflators to include an additional 35 to 40 million inflators.

The additoinal units to be recalled would be added to an already massive recall, considered the largest in U.S. auto history that involved 28.8 million inflators. The expanded recall is set to take place starting May 2016 through December 2019.

"Today's action is a significant step in the U.S. Department of Transportation's aggressive oversight of Takata on behalf of drivers and passengers across America. The acceleration of this recall is based on scientific evidence and will protect all Americans from air bag inflators that may become unsafe," said Transportation Secretary Anthony Foxx.

This latest twist is part of the Takata saga that has been going on since 2008, when the manufacturer had to call back 4,000 automobile as a result of faulty air bags. The new recall will bring the total to more than 50 million vehicles fitted with Takata air bags that have had to be recalled.

At least 11 deaths and about a dozen of injuries have been linked to Takata's faulty airbags. Despite Takata's claims to the contrary, it has been looking more and more like the cause of the problem is the parts maker's use of ammonium nitrate to inflate the airbag in case of a collision.

The volatile chemical, along with heat and humidity, has been the top culprit in the dangerous deployment of Takata airbags. The ammonium nitrate is suspected of inflating airbags with such force that the chemical shatters its container, spraying shards of metal at vehicle occupants.

"The science clearly shows that these inflators become unsafe over time, faster when exposed to humidity and variations of temperature. This recall schedule ensures the inflators will be recalled and replaced before they become dangerous, giving vehicle owners sufficient time to have them replaced before they pose a danger to vehicle occupants. NHTSA will continue to evaluate all available research and will act quickly to protect safety," said NHTSA Administrator Mark Rosekind

Takata has until 2018 to prove to regulators that the ammonium nitrate is safe to use, and the company will have to start recalling all of them if they're confirmed to be dangerous. The company also agreed to no longer use the chemical for new contracts.

While it has, over the years, argued in favor of the continued use of ammonium nitrate, Takata began building a drying agent into its airbag builds to keep the volatile chemical in check. This move by the Japan-based supplier looks like acceptance of the true cause on Takata's part, said Scott Upham, CEO and founder of Valient Market Research, an automotive consulting firm.

"Finally, there's enough scientific evidence to point to the humidity issue as affecting the propellant," Upham told the New York Times. "For a long period of time, they denied that ammonium nitrate was to blame. But this does validate there are fundamental issues with the chemical itself."

The NHTSA advises vehicle owners to immediately act upon receipt of notification that a remedy is available for their vehicle.

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