At least 17 people have died and more than 180 injured due to the problem. These inflators have caused the largest automotive recall in U.S. history with 42 million vehicles and up to 69 million inflators being called back for repairs.
The latest recall is the first involving the inflators that use calcium sulfate as a drying agent. The inflator can combust in an “overly-aggressive” manner, potentially rupturing and causing harm, according to a filing Takata submitted to the highway safety administration.
Takata uses the ammonium nitrate as an oxidizing agent to inflate air bags, which may deteriorate when exposed to high airborne humidity and temperatures. Previously the company believed that this particular drying agent, calcium sulfate (Ca2SO4), stopped the propellant from degrading, but now suspects that desiccant is inadequate and is a potential hazard.
Takata originally used a toxic airbag propellant called sodium azide. But that compound is volatile and could release toxic fumes into the car when the airbags deployed, especially if damaged. Ammonium nitrate, they concluded, would do the job more effectively and at lower cost.
In 1981 Mercedes-Benz was the world’s first automobile manufacturer to present the airbag and a propellant driven belt tensioner as restraint systems to the public in a series-production car. American manufacturers followed suit and delivered their first test fleets with compressed-air operated airbags, these restraint systems—which were conceived as an alternative to seat belts—sometimes led to serious injuries and in a few cases even fatalities.
Autoliv, a Swedish-American automotive safety products manufacturer, said in 2014 that it avoided using ammonium nitrate because of stability issues. Key Safety Systems, the recent buyer of Takata’s bankrupt assets, said at the time that it used guanidine nitrate and tetrazole—which experts said was more expensive but less risky and more durable than ammonium nitrate. TRW Automotive, a large supplier of safety parts based in Michigan, also used a propellant based on guanidine nitrate.
The National Highway Traffic Safety Administration now says that tests done by Takata show that—for the first time—this type of calcium sulfate-desiccated inflator “will pose a safety risk if not replaced.” The agency says it has no reports of any inflators with this desiccant actually rupturing.