Ammonium nitrate was about one-tenth the price of tetrazole, according to Upham, who also reviewed industry patents. But ammonium nitrate had a critical flaw that he says led other air bag makers to give up on it: Ammonium nitrate has five phases of varying density that make it hard to keep stable over time. A propellant made with ammonium nitrate would swell and shrink with temperature changes, and eventually the tablet would break down into powder. Water and humidity would speed the process. Powder burns more quickly than a tablet, so an air bag whose propellant had crumbled would be likely to deploy too aggressively. The controlled explosion would be just an explosion. “Everybody went down a certain road, and only Takata went down another road,” says Jochen Siebert, who’s followed the air bag industry since the 1990s and is now managing director of JSC Automotive Consulting. “If you read the conference papers from back then, you can actually see that people said, ‘No, you shouldn’t. It’s dangerous.’ ”
When Lillie and other Moses Lake engineers met with their ASL colleagues in December 1998 to review a new design using ammonium nitrate, Lillie says they were told the phase stability problem had been solved. He rejected the design nonetheless. ASL wasn’t able to provide documented evidence of the safety of its product, he said in a January 2016 deposition, taken as part of a personal injury suit against Takata and Honda. “Never any evidence, never any test results, never any test reports, nothing to substantiate they had overcome the phase stability problem,” Lillie testified.Sadly, the bosses at Takata ignored the bad news, and pushed forward. I hope to never be in the situation at the Takata engineers found themselves in, and if I do, I hope I have the courage to speak out.