WASHINGTON -- Having established a root cause for Takata's deadly airbag inflator ruptures, automakers probing the faulty parts are shifting their attention to other key questions that must be answered before the industrywide crisis can be resolved.
Chief among them is how well the replacement inflators being installed in millions of vehicles perform in the field, according to David Kelly, project manager for the Independent Testing Coalition, the 10-automaker consortium investigating the defect.
Kelly said the scope of the investigation's second phase is being finalized. Along with the performance of replacement inflators, the group will look into differences in behavior between passenger- and driver-side inflators as well as the performance of newer formulations of Takata's ammonium nitrate propellant that use a desiccant, a chemical additive used as a drying agent.
The coalition, convened about a year ago, brought some measure of clarity to the Takata crisis last week by establishing why some of the roughly 23 million airbag inflators declared defective last year would explode in a crash.
Working with the aerospace company Orbital ATK, the coalition concluded that the ammonium nitrate propellant used in Takata's inflators was a key factor in the ruptures, but it also cited two others: problems with the construction of the inflators that allowed moisture to seep in, and prolonged exposure to humidity and temperature swings.
After such exposure, ammonium nitrate, a volatile explosive used in open-pit mining, can become unstable and combust violently, turning a normal airbag deployment into an explosion powerful enough to break its metal container and spray vehicle occupants with metal shards. Such explosions have been linked to 10 deaths and more than 100 injuries.
Several years ago, Takata began adding a desiccant to its ammonium nitrate propellant but continued to make some inflators without the additive. All inflators involved in the recalls lack a desiccant.
Safety regulators are pressing Takata, automakers and other airbag suppliers to speed delivery of replacement inflators to dealerships, and two lawmakers last week called on them to move more urgently. But regulators acknowledge that early replacement parts made by Takata may have the same defect as the recalled inflators they replaced and may need to be replaced again.
The newer parts are viewed as safer for now because they haven't been exposed over time to temperature swings in humid climates, but Kelly said the replacements need to be tested for investigators to understand how they perform in the field.
One challenge for the coalition will be getting those parts, while suppliers are straining to produce enough to meet consumer needs and recall completion targets.
Kelly said a National Highway Traffic Safety Administration order that allocated the coalition an allotment of Takata inflators retrieved from recalled vehicles for its root-cause investigation could provide a framework for procuring replacement parts to be tested.
"We do not have the logistics worked out yet, but we do not want to get in the way of the consumer getting their replacement parts," Kelly said.
The coalition also is working under a ticking clock. Under a consent agreement with NHTSA, Takata faces an end-of-2019 deadline to prove to regulators that its ammonium nitrate propellant is fundamentally safe.
"We are aware of the deadline that Takata has to meet," Kelly said. "If we have anything to add to that discussion, we want to be able to provide it with enough time in advance of those deadlines to inform the debate."
Also weighing in on the debate will be safety advocates such as Sean Kane, who disputed the coalition's root-cause finding.
"Ultimately the use of phase-stabilized ammonium nitrate is the pillar of the problem, and nobody wants to acknowledge that," said Kane, president of Safety Research & Strategies Inc.
Takata has agreed to shift from using ammonium nitrate. But if it can't meet the burden of proof set out by NHTSA, it could face a recall of every ammonium nitrate inflator it has ever produced, which would add tens of millions of U.S. vehicles to the recalls and pose a daunting task for the Takata customers that constitute the coalition: Toyota, Honda, Fiat Chrysler, BMW, Ford, General Motors, Mazda, Mitsubishi, Nissan and Subaru.
Kelly said that is not the coalition's focus now.
"We haven't been down that road," he said. "We've only talked about finding a root cause and finding an ultimate solution for the safety of the inflators."
