A senior official of Japanese auto parts maker Takata said Tuesday that the company is still searching for the main cause of deadly explosions in its airbags.
Kevin Kennedy, executive vice president at Takata's US arm TK Holdings, told lawmakers that the company has already focused on the possible instability of the main ammonium nitrate propellant in airbag inflators in certain conditions.
But that is not the only issue, he said, and "we do not have the definitive root cause."
US legislators pressed the company on why it continued to manufacture inflators with the explosive chemical, arguing that it appears to be the reason why dozens of Takata airbags have inflated with excessive force, powering metal shrapnel into drivers and passengers, leaving at least six dead.
Ten automakers are being forced to recall some 34 million cars inside the United States alone to replace the inflators.
Kennedy said many of the replacements will use the same chemical, which appears to become unstable after years of exposure in hot and humid climates.
Research "seems to indicate that ammonium nitrate is certainly a factor in the inflator ruptures," Kennedy conceded. But "There are indeed many other factors."
He mentioned the lack of desiccant to keep the inflators dry, and the shape of some of the ammonium nitrate wafers inside the detonators as additional factors.
"Without really exactly understanding the root cause and continuing the tests outside the boundaries, we're trying to really understand what the total scope is," he said.
Kennedy said Takata and other parts makers have stepped up production of replacement airbags and inflators to reduce the dangers, but many of those from Takata still use ammonium nitrate.
Over time, Kennedy said, they will replace the chemical with another.
"I think over all you will see ammonium nitrate production go down," he said.