TOKYO -- Global automakers may face another potentially huge airbag recall as top U.S. auto safety regulator evaluates the long-term safety of inflators made by bankrupt supplier Takata.

The manufacturing entity left after the supplier’s implosion faces a Dec. 31 deadline to show the National Highway Traffic Safety Administration that as many as 100 million inflators containing a chemical drying agent will be safe long-term.

Those would be on top of the previous round of recalls, which started in 2008 and is linked to at least 23 deaths worldwide and more than 200 injuries in the U.S. alone. Takata had sold defective airbag inflators using ammonium nitrate, which were at risk of exploding violently in a crash and injuring passengers with metal shards.

The Japanese parts maker pleaded guilty to a wire-fraud charge as part of a $1 billion settlement with the U.S. Justice Department over the airbag problems, and later went out of business and its assets were acquired by China-owned Joyson Safety Systems.

If the supplier can’t demonstrate the safety or durability of newer desiccant-equipped inflators, the U.S. agency may order that they be recalled as well. The total bill for another massive recall could reach tens of billions of dollars, with carmakers bearing the brunt of the costs.

“NHTSA is carefully reviewing information regarding the safety of desiccated inflators to determine appropriate next steps,” the agency said. It typically takes the NHSTA as long as 6 to 12 months to issue an official recall after it collects enough data.

TK Services, the entity left with Takata’s operations, didn’t respond to requests for comment. Yoichiro Nomura, a representative of TKJP, the legal entity that absorbed Takata’s debts, declined to comment.

Under a 2015 consent order, Takata airbag inflators using ammonium nitrate, a widely-used chemical explosive, were progressively banned because the propellant tended to become unstable in humid climates. Years before, because of this risk, Takata added a chemical drying agent to its inflators and also used them to replace defective parts.

Takata initially sought to limit the initial batch of airbag inflator recalls based on specific types and location, but as more injuries and deaths mounted, all units using ammonium nitrate were recalled, with the exception of those equipped with the drying agent while Takata and others in the auto industry studied their long-term safety.

“NHTSA reserves the right to order Takata to phase out of the manufacture and sale of the desiccated Takata PSAN inflators if NHTSA determines that such a phase out is required by the Safety Act,” the agency said in the consent order.

Given that a decade’s worth of desiccant-equipped inflators were made since 2008, the NHSTA may order a similar number of units to be recalled, according to Scott Upham of Valient Market Research, a provider of automotive safety analysis and research.

'They are on the hook'

“The automakers and the suppliers, they all knew this was coming,” Upham said. “They are on the hook. Because of Takata’s bankruptcy, they are going to have to cover 100 percent of the costs.”

A group of automakers involved in the recalls commissioned durability tests of the desiccant-equipped airbags and presented their findings to NHTSA in early October. The group, known as the Independent Testing Coalition, found that the drying agent provided significant protection. The group recommended a monitoring program for one inflator design in the riskiest climates while telling NHSTA that it believes the parts present no immediate safety risk.

“After 30 years of predicted aging, none of the studied inflator designs and propellant combinations predicted detrimental effects, except those subjected to the most severe conditions and vehicle temperature,” David Kelly, the ITC’s program director and a former NHTSA acting administrator, said in an October statement.

Even as the possibility of another massive recall looms, it would be on top of a recent expansion of Takata airbag recalls. On Dec. 5, Takata told the NHTSA that another 1.4 million vehicles would have to be repaired.

Previous efforts

Some automakers have already taken steps to recall desiccant-equipped airbags. In March, Honda Motor Co. voluntarily recalled about 1.1 million vehicles in the U.S. to replace inflators with the drying agent, which were installed in an earlier round of recalls. Honda said that the desiccant installed in Takata’s airbags may have absorbed excessive moisture when they were manufactured in Mexico, potentially making the problem worse.

“During storage and assembly, the drying agent may have absorbed moisture, and may have been installed onto the inflators with a high degree of water content,” said Teruhiko Tatebe, a spokesman for Honda.

Tatebe said the company will continue to work with NHTSA to analyze all available data in order to determine the durability and safety of desiccant-equipped airbags.

“This is a story that should be out there,” Upham said. “The next recall could be on the same scale of the original.”