Critics disagree. Mark Lillie, a former chemical engineer at the Moses Lake plant, was asked to conduct an engineering review in 1999 when the company debated a proposal to switch propellants.
Engineers from Takata's Automotive Systems Laboratory in suburban Detroit argued that ammonium nitrate would be stable if mixed with the right additives.
"Our answer was, 'We don't think so,'" recalled Lillie, who left the company later that year. "I literally said at the time that someone is going to be killed if we go forward with this, and indeed that's what happened."
Lillie, who is now retired and living in New Mexico, says moisture isn't the only environmental factor that can degrade ammonium nitrate. The propellant also is sensitive to temperature swings.
Takata was aware of these problems, Lillie contends. After launching production in 2000, the company obtained at least five patents to make ammonium nitrate more stable.
Paul Worsey, an explosives expert at the Missouri University of Science and Technology, has examined those patents. He argues that ammonium nitrate's basic weaknesses -- sensitivity to moisture and heat swings -- cannot be neutralized.
"It's like flogging a dead horse," Worsey said. "They keep trying to fix it, but it's one of the worst materials to work with. I can see what they're trying to do, but it's a technological nightmare."
In an emailed statement, Takata's Levy noted that the company "routinely" files patents to protect its intellectual property. Levy added that Takata "has always understood the effects that moisture may have on the combustion characteristics of ammonium nitrate."
Other airbag suppliers have steered clear of ammonium nitrate. Autoliv Inc. and TRW Automotive, for example, use propellants made from guanidine nitrate, which is less sensitive to moisture and heat.
The replacement inflators produced by both Autoliv and TRW for Honda and other automakers use guanidine nitrate propellant. But Takata has stuck to its guns, contending that ammonium nitrate is safe if manufactured properly.