The agency appears to be focusing on how vehicle design affects inflators over time, taking into account factors such as cabin sealing against humidity or moisture intrusion, according to Reuters.
“Think about age, high humidity, all the different factors,” NHTSA head Mark Rosekind told reporters ahead of a formal announcement scheduled for Tuesday. “Now you add design of the vehicle.”
The agency has broadened the scope of its inquiry “beyond the 11″ automakers affected by the initial rounds of recalls. Previous reports suggests the probe could even expand to include any airbag inflator that uses ammonium nitrate, the controversial propellant is believed to explode with too much force, rupturing the inflator capsules, due to years of moisture exposure.
Rosekind claims that tests show Takata’s newer inflators to be “solid,” though GM just recently issued a recall campaign for 2015 models after Takata’s production-lot testing resulted in a ruptured side-airbag inflator.
The Takata campaigns so far have affected nearly 20 million vehicles sold in the US market.