Takata Air-Bag Problems Are Linked to Multiple Factors
Report to company, regulators says the issues likely allowed moisture to enter air-bag inflater
By Yoko Kubota And Eric Pfanner in the Wall Street Journal
TOKYO—A German research institute investigating the air bags at the center of the world’s largest automotive recall has identified at least four factors that could lead to deadly explosions, underscoring the complexity of the problem.
The German organization, Fraunhofer ICT, outlined the findings in a confidential report for air-bag maker Takata Corp. of Japan, regulators and nearly a dozen auto makers. Takata, representatives of groups of auto makers, and the head of the U.S. National Highway Traffic Safety Administration were expected to use the report’s findings as the foundation for a scheduled update to U.S. lawmakers on Tuesday. An individual who reviewed the Fraunhofer report spoke to The Wall Street Journal.
The factors are all said to lead to the possibility of moisture entering the air-bag inflater, where it damages the propellants that deploy the bag in a crash. Explosions related to defective inflaters have been linked to at least six deaths.
The complexity of the problem and the inability to pinpoint a single reason underscore why the recalls have spread to 53 million vehicles world-wide, even though only a handful of air-bag inflaters have ruptured, against thousands that were tested.
Areas of Focus
Experts commissioned by Takata found a number of factors that could allow moisture to enter the inflater, which could lead to malfunction
- Damaged or problematic inflater components, such as the O-ring
- The positioning of the inflater and air-bag system in the vehicle
- Prolonged exposure of the vehicle to high humidity and temperature
- Inflater manufacturing variations
“I know there may not be a single root cause, and we may in fact never know the root cause,” NHTSA head Mark Rosekind said in remarks prepared for testimony before a subcommittee of the U.S. House of Representatives.
The four factors listed by Fraunhofer in the interim report are damaged or problematic inflater components; the positioning of the inflater and air-bag system in vehicles; prolonged exposure to heat and humidity; and manufacturing variability.
In an example of the first factor, according to the individual who has reviewed the report, problematic O-rings used to seal containers could be playing a role in allowing moisture into inflaters.
“Currently, the work suggests that the period of product use as well as continuous exposure to climate of persistent heat and high humidity are factors with impact, but we believe we need to continue studying other factors,” said Hideyuki Matsumoto, a Takata spokesman.
Fraunhofer declined to comment.
Takata, auto makers and regulators have cited another potential problem with components: The aluminum tape used to seal holes in certain types of inflaters. In some cases, the adhesive appears to fail after years, allowing in moisture.
Air-bag inflaters are generally sensitive to moisture because they contain explosives, which could change form or malfunction when they absorb moisture. But for Takata, moisture appears to be a particular problem because of the sensitivity of ammonium nitrate, the chemical it uses in its propellants.
Ammonium nitrate is a widely used explosive, but Takata is the only major maker of air-bag inflaters to use it in its propellant chemical mix. The chemical is especially prone to absorbing moisture and is sensitive to temperature change, which can cause its volume to fluctuate, experts said. Takata said it uses other chemicals in its mix to stabilize ammonium nitrate to prevent volume change.
Fraunhofer found that when moisture mixes with the propellants, the stabilized ammonium-nitrate particles could cluster. Such changes could lead to expansion of the propellants’ surface area, which could prompt them to burn at a faster rate than designed, according to the individual. That faster burn could lead to gas being emitted faster and more forcefully than the inflater’s metal casing can contain, leading to an explosion.
Last month, Takata said it plans to stop using batwing-shaped wafers in side air bags while continuing to employ stabilized ammonium nitrate in its propellant mix in inflaters. It says the propellent “is safe and effective for use in air-bag inflaters when properly engineered and manufactured,” said Robert Rendine, a Takata spokesman at Sard Verbinnen & Co.
Takata said it plans to replace older inflaters with its own newer versions as well as those made by rival companies. Auto makers will replace some air-bag inflaters that were installed to repair vehicles in previous recalls.
Takata’s newer inflaters include desiccants to prevent moisture-related problems, people knowledgeable about the matter have said.