In a dramatic expansion of what is already the largest automotive recall in history, Takata Corp.—which recently filed for bankruptcy protection—has just added 2.7 million vehicles to the total.
NHTSA has determined the root cause of the problem is airbags that use ammonium nitrate-based propellent without a reliable chemical drying agent, i.e., without an effective desiccant. Environmental moisture, high temperatures, and age contribute to the process that can disastrously and explosively overinflate the airbags’ inflator mechanism.
Vehicles made by Ford, Nissan and Mazda are using a type of airbag inflator including a desiccant, or drying agent, that previously was thought to be safe. Commonly encountered desiccants are solids that absorb water. They are commonly used in packaged foods to retain crispness and are in no way explosive in their own right.
However the desiccant’s role in the Takata airbag inflation mechanism is to prevent the propellant, largely ammonium nitrate, from becoming hydrated and therefore unstable. In chemical terms instability can affect the burn rate of the compounds and behave unpredicably leading to malfunction.
Ammonium nitrate is an inexpensive propellant that cycles through five solid states depending on temperature. Generally this occurs in a predicable way and as the vehicle goes from the heat of sunshine to the cold overnight, the temperature swing is large enough for the ammonium nitrate to change from one phase to another. Ammonium nitrate also absorbs moisture from the atmosphere readily, hence the need for a desiccant to keep the compounds dry. The desiccant is there to stabilize this process and, if it fails, may make ammonium nitrate dangerous, engineers say.
Exposure to moisture and temperature fluctuations can degrade the propellant ammonium nitrate, the volatile compound Takata’s inflators use to deploy airbags. The company has used a variety of chemical agents to keep the propellant dry in its devices over the years, with some combinations showing a greater propensity to fail than others, federal regulators said.
The real problem is that the inflators have an unacceptable failure rate due to occasional fragmenation of the metal inflator housing blasting shrapnel into the passenger compartment. Due to aging and humidity, the propellant that inflates the air bag oxidizes fuel granules and wafers explosively causing the inflator’s casing to rupture, and blasting the shattered fragments with sometimes lethal velocity.
Ford, Mazda and Nissan installed these inflators in vehicles manufactured for the United States market from 2005 through 2012, according to Takata. All are on the driver’s side of the vehicles. The affected vehicles are from the 2005 through 2012 model years.
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.
Takata said in documents filed with the safety agency that it tested the inflators returned from Nissan and Ford vehicles which use calcium sulfate as a drying agent. Although none of the inflators actually ruptured, some showed a pattern of deterioration in the ammonium nitrate propellant over time “that is understood to predict a future risk of inflator rupture.”
NHTSA said in a statement that not all Takata inflators with a desiccant are being recalled. Takata used different drying agents in its other inflators, the agency said.
Nissan said the new recall affects just over 515,000 Versa subcompact hatchback and sedans from the 2007 through 2012 model years. Mazda said its recall covers about 6,000 B-Series trucks from 2007 through 2009. Ford, which has the most vehicles involved in the latest recall, is reviewing the information and will file a list of models within the time required by law.
The latest recall raises doubts about the safety of other Takata Corp. inflators that use ammonium nitrate and drying agents. The doubts over Takata’s propellant raise questions of whether the recalls should be limited to humid regions.
For as far back as 2014 NHTSA said that it would urge automakers to expand recalls of certain drivers’ side airbags that had previously been limited to states and territories with high humidity. The company has now agreed to recall all original equipment inflators without a drying agent in phases by the end of 2018. NHTSA gave Takata until the end of 2019 to prove that inflators with the drying agents are safe, or they must be recalled as well.
Takata pleaded guilty to criminal charges in January 2017 and agreed to pay a $1 billion fine related to its faulty airbag inflator systems. After filing for bankruptcy protection in June, it is selling assets to be able to continue manufacturing components.
The company has said that it expects to fund the airbag repairs through the asset sale and that it has secured financing to ensure it can continue operations, including dealing with the defective inflators, while it restructures.
NHTSA said Takata has assured the agency that it will keep making inflator parts available.
“This recall now raises serious questions about the threat posed by all of Takata’s ammonium-nitrate-based airbags,” Senator Bill Nelson, Democrat of Florida, said in a statement. “If even more are found to be defective, it will take us from the biggest recall ever to something that could become mind-boggling.”
The agency is urging people whose inflators have been recalled to get them replaced as soon as possible. To find out if your car or truck is part of the recall, go to nhtsa.gov/recalls or airbagrecall.com and key in the 17-digit vehicle identification number.