'It turned it into shrapnel'
The new airbag came not a moment too soon for Takata.
The Japanese supplier had been making seatbelts in the United States since the mid-1980s, but its airbag business, which it began in earnest in the 1990s, was in trouble.
A previous generation of airbags supplied to Nissan had the problem of deploying too forcefully. Those airbags were linked to at least 40 eye injuries in the 1990s.
Takata began experimenting with alternative propellants. But in 1997 its inflater plant in Moses Lake, Wash., was rocked by a series of explosions that destroyed equipment and greatly curtailed production, according to insurance claims made by the company at the time.
After the blast, Takata was forced to buy inflaters from competitors and airlift them to automakers across the country. The company's American business struggled "to maintain corporate viability," Takata said in a lawsuit filed against its insurer.
It was against that difficult backdrop that Takata embraced the cheaper new compound, ammonium nitrate, in its airbag inflaters, according to former employees. Mark Lillie, who had worked as an engineer at Takata, told The New York Times in 2014 that considerations over cost spurred the supplier to use the compound, despite the dangers associated with it. Mr Lillie raised concerns over the risks in the late 1990s, but his warnings went unheeded.
Around the same time, the team at Autoliv was asked to study the Takata design. Mr. Taylor, the head Autoliv chemist, said his team immediately recognized the risks posed by the ammonium nitrate.
"We tore the Takata airbags apart, analyzed all the fuel, identified all the ingredients," he said. The takeaway, he said, was that when the airbag was detonated, "the gas is generated so fast, it blows the inflater to bits."
Mr. Hock, the former member of Mr Taylor's team, said he recalled carrying out testing on a mock ammonium nitrate inflater that produced explosive results that left his team shaken. "When we lit it off, it totally destroyed the fixture," he said. "It turned it into shrapnel."
The former Autoliv scientists said that they considered their verdict against the ammonium nitrate irrefutable, so much so that they understood Autoliv had alerted other automakers to the danger.
An Autoliv spokesman declined to comment on the company's dealings with its automotive customers, which at the time also included Chrysler, Ford, Honda, Mazda, Mitsubishi and Toyota. Those automakers all started using Takata's airbags in the early to mid-2000s.
Fiat Chrysler declined to comment, while Honda, Mitsubishi and Toyotasaid that they had not located any pertinent information from that period.
"There was no industry understanding in the late 1990s" that ammonium nitrate propellants, or explosives, were risky, Matt Sloustcher, a Honda spokesman, said in an emailed statement.
Autoliv's concerns were backed by well-known research. Widely available studies going back decades warned of the tricky properties of ammonium nitrate, which can break down when exposed to moisture or temperature changes — vital factors, federal regulators said, with the defective Takata airbags.
"Some of the worst industrial accidents at the worldwide level involve ammonium nitrate," Luigi T. De Luca, an Italian academic and a leading expert in solid propellant rockets, said in an email.