Takata Corporation has become well known as a lesson in product safety, thanks to their deadly airbags which were installed in cars worldwide. Despite filing for bankruptcy in 2017, their shadow lingers on as the biggest product recall in history continues to grow ever larger. Over time, the story grows deeper, as investigators find new causes for concern and deaths continue to mount.

In late 2019, another Takata recall was announced — one which caused fresh worry among industry officials familiar with the case. Up to this point, the defective parts produced by Takata were the models based on ammonium nitrate propellants, a chemical that other manufacturers had deemed too dangerous to use. However, there have been reports of other models using different chemistries having fatally injuring motorists, raising the question of whether any Takata airbag could be considered safe.

Problems, Plural

After years of research, both internally and by outside investigators, the problem seemed settled. Takata had chosen to use a propellant that became unstable over time, thus leading to overpressure events which could destroy the metal airbag casing, causing injuries and fatalities to drivers and passengers. It was believed that this affected only the phase-stabilised ammonium nitrate (PSAN) airbag inflators. This chemistry was only used by Takata, as other manufacturers had deemed it too dangerous for practical use.

In 2019, everything changed with the first recalls for Takata’s NADI 5-AT inflators. NADI stands for Non-Azide Driver Inflators, which use a tetrazole propellant, widely considered safe when used properly. Takata NADI airbags in cars produced between 1996 and 2001 are reported to have taken two lives in Australia, This is on top of the existing 24 deaths and 300 injuries worldwide caused by Takata’s PSAN inflators.

According to Takata’s submission to the National Highway Traffic Safety Administration, the issue is caused by a defective foil seal, which fails to prevent moisture ingress into the airbag casing. Moisture ingress can have several negative effects on inflator performance. It may cause slow deployment of the airbag, reducing its effectiveness at restraining passengers in the event of a crash. Alternatively, through repeated cycles of moisture ingress and drying or freezing, the propellant may mechanically break down, increasing its surface area.This leads to an increased rate of reaction, creating the overpressure events that shatter casings, spraying passengers with deadly shrapnel.

I reached out to John Keller, a former Takata engineer from 1998-2001, for comment on these recent developments. John undertook studies into the performance of airbag products at the time, collecting data on a variety of models. According to John, “Propellant surface area is critical. If there’s too much propellant surface area, relative to the vent area, during combustion the inflator housing can fracture […] It’s important regardless of the propellant formulation […] The increase in propellant surface area from the broken propellant could cause the inflator to rupture.”

In the cases of deaths and injuries caused by Takata airbags, the primary cause has been due to metal fragments ejected by the airbag. In practice, this has led minor accidents involving airbag deployments to become casualty events. Drivers are being instructed to avoid driving their vehicles in some cases, with automakers doing mobile inspections or towing vehicles to dealerships.

Getting To The Root Cause

As pictured in the video above, faulty inflators deploy with violent results. Understanding the cause behind this is key to solving the problem. With recalls now affecting multiple different Takata airbag chemistries, it is no longer realistic to place the blame solely at the door of ammonium nitrate. Instead, it hints at a broader issue in design and manufacture. In the case of the NADI inflators, the problem is an imperfect moisture seal. With regards to the PSAN inflators, similarly humidity and moisture are blamed.

In November 2015, The NHTSA gave Takata until December 31st, 2019 to prove that PSAN inflators featuring a dessicant were safe to use. Thus far, the federal agency has not commented definitively on the issue, which would lead to a recall of yet further vehicles. According to Keller, “That remedy is not fundamentally sound. It’s an illusion of a remedy that may persuade some people, but not anyone who truly understands Takata’s inflator defects. Eventually any desiccant will saturate, once that happens, moisture goes into propellant.”

The common thread here is the effect of moisture ingress on propellant stability. With multiple airbag types now affected, it’s clear that the broader issue at play is one of poor inflator design, not simply the selection of the wrong propellant chemistry. This should raise alarm bells for other airbag manufacturers, who can no longer consider themselves safe for having avoided the use of ammonium nitrate in their designs. Instead, it goes to show that rigorous attention must be paid to the long-term stability of the propellant charge. Failure to control this issue can lead to tragic results.

Given the long lifetime of the average automobile, the public have reason to expect airbags to remain safe over many decades of use. Any protection method that comes with a time limit, such as a dessicant, seems likely to cause more problems down the road. As more and more cars with airbags reach old age, there remains the possibility that more airbags will suffer dangerous failures. Thus far, other manufacturers have largely avoided major issues with degradation on a timescale of multiple decades, but whether these devices can remain safe over 40 years, 50 years, or further, remains an open question. At these timescales, this only affects a tiny fraction of motorists driving vintage vehicles, but one that the community will have to face nonethelesss.

Moving Forward

The timescale involved confounds efforts to solve the problem. As the latest NADI recalls cover vehicles of a greater age, it becomes difficult for automakers to remedy the issue. BMW estimate it will take between 14 and 22 months to develop and produce replacement parts. Along with Toyota, they are the only manufacturers intending to do so. The business case for redesigning parts for a small fleet of cars up to 25 years old is a poor one, due to the huge engineering and logistical expensive involved. Other companies are instead exploring buyback programs to compensate consumers for their vehicles that are no longer safe to drive.

Airbags are not a part that can readily be treated as a consumable, due to the dangers involved in their installation and handling. With these constraints in place, research will be required to ensure airbags can withstand such extended environmental exposure without becoming dangerous to vehicle occupants. Most manufacturers have thus far succeeded in this task; time will tell if they can keep up the good work.

The fact that multiple branches of Takata’s technology has proven fatal suggests a deeper problem at the company, rather than one fateful poor decision. Manufacturing defects were allowed to flow out to customer vehicles, leading to the loss of several lives and countless further injuries, some of which are permanently life-altering. Against that background are the devastating economic consequences, which have affected the livelihoods of many who worked for Takata or related companies. It’s clear that rigorous change is required from automakers and suppliers to ensure such a disaster is not allowed to happen again.