Earlier this week Japanese auto part maker Takata announced it may have to call back some of the millions of airbags already replaced because they may still have a tendency to shoot shrapnel upon deployment. Today, the company released an estimated number of re-recalled airbags, to the tune of 400,000.

Bloomberg reports that the airbags which were already replaced once represent about 10% of the nearly 4.1 million driver-side safety devices recalled worldwide.

Takata executive vice president for North America Kevin Kennedy said that the airbags in need of a second replacement will be serviced after the 34 million vehicles still waiting for their first recall remedy.

During a U.S. House committee hearing earlier this week, Kennedy blamed the need to circle back and fix the already replaced airbags on a certain type of inflator called a batwing.

“The final stage of the recalls will include the replacement of batwing driver inflators that were previously installed as remedy parts in prior recalls,” Kennedy said. “Takata has also committed to cease producing these types of driver inflators.”

The batwing inflator was used to hold Takata’s unusual chemical component, ammonium nitrate.

The chemical has been a topic of discussion among regulators and investigators trying to determine why the Takata-produced airbags explode with such violent pressure.

Chemicals have long been the powerful mechanism behind airbags. That’s why after some crashes, the driver or front-seat passenger in a vehicle may have chemical burns on their skin.

Typically the inside of an airbag contains an igniter that heats an aspirin-sized tablet of compressed chemical. The ensuing reaction fills the airbag with gas, inflating it at speeds reaching a few hundred miles per hour.

Takata began using ammonium nitrate in its airbags in the late 1990s, because of the chemical’s ability to make airbags inflate in a matter of milliseconds.

Since the company began making replacement parts for the recalled vehicles, it claims to have added materials that gather and hold moisture to the chemical mix in an effort to make the device safer.

Kennedy said the company will phase out the use of the propellant.

Takata’s decision to call back airbags that have already been replaced gives credence to consumer advocates’ worries over the safety of Takata’s replacement airbags, given that the company – along with investigators for the National Highway Traffic Safety Administration and automakers – have yet to find a root cause for the airbag ruptures.

Takata Said to Plan to Replace 400,000 Air Bags Previously Fixed [Bloomberg]

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