Propellant ‘ fix’ may not stop airbags exploding
WHILE the U. S. Senate reviews its most recent report on why old Takata airbags explode, the team of rocket scientists tasked to investigate the issue will begin testing the fix introduced to airbags’ propellant to see if they are safe.
To date, the U. S. Centre for Auto Safety lists five deaths, nine serious injuries, with at least two victims having metal pieces lodged in their eyes, permanently damaging their eyesight.
One of these victims was Airforce Lieutenant Stephanie Erdman. She had a minor bumper bashing in Florida in 2013 in a 2002 Honda, which set off her airbag. Only, instead of explosive inflating a cushion, the metallic inflator exploded, sending metal shards into the cabin.
“My passenger only had mild scrapes and bruises,” she told lawmakers. “I should not have been injured in the shocking and terrifying way that I was,” Erdman told the senators.
A jagged piece of metal shot through Erdman’s airbag and imbedded itself in her right eye, while also fracturing her right nasal bone. At the hearing last Thursday she displayed a graphic photograph of herself with a chunk of metal protruding from her right eye. “I was instantly blinded on my right side,” she said. “I felt blood gushing down my neck. I was terrified. My vision will never be the same. I will never be the same.”
Police who find the victims in their cars liken the shrapnel wounds to being shot or stabbed.
Takata executive Hiroshi Shimizu, who also testified at the hearing, apologised to the victims. “We are deeply sorry and anguished,” he said.
New instead of old grenades
Meanwhile, installation of the airbags continues. The 10 automakers who installed the airbags called in a team of rocket scientists to perform an independent investigation. These rocket scientists are due to announce their findings soon.
Led by Bob Wardle, a PhD chemist with 30 years at Orbital ATK, the aerospace company hired to investigate the reason why Takata’s airbags exploded, told the Quartz web paper it’s not just manufacturing problems, as Takata has alleged, but a fundamental flaw in the design that has turned the airbag’s inflator into a bomb.
“A rocket motor is big and it flies through the air, but as far as what happens inside of it, there is a signal that comes in, an ignition train that starts a process, a main propellant that burns,” he told reporters.
“In the case of a rocket motor you have a single nozzle on the end of it; in the case of an airbag inflator, gases are used to open an airbag instead.”
Wardle’s team developed a detailed analysis that considered 63 different ways the airbag system could go wrong, using computer models and reams of data to test each possibility.
Ultimately, they found the problem in the solid propellant used to inflate the airbag.
Based on ammonium nitrate, that propellant is a cheaper but more volatile fuel than Takata had previously used.
When the fuel is installed in the inflator, it is typically “in the shape of a wafer or bat wing”, Wardle said, but it changes shape when exposed to humidity over time. When the airbag is triggered, the change in the fuel’s shape leads to to an unexpected increase in pressure that detonates the inflator instead of filling the airbag.
The force of the explosion hurls pieces of the inflator into the cabin like shrapnel, injuring those in the vehicle.
The report concluded that the inflator’s design is not sufficient to protect it from heat and water.
Takata had previously surmised that humidity was behind the flaw, but blamed the issue on aging parts, unusual conditions and a manufacturing plant that hadn’t followed instructions while assembling the inflators.
Later, it added a drying agent to the propellant in new airbag inflators that would temporarily keep them from changing shape in humid conditions.
The revelation that the inflator assembly itself is flawed led to criticism of the safety agency for allowing Takata to install airbags with the drying agent as a temporary solution.
Florida senator Bill Nelson said after a hearing on the Takata airbags in February that the 10 car builders who had installed the Takata fix were selling cars with “new live grenades as replacements for the old live grenades”.
But the National Highway Traffic Safety Administration is reluctant to expand its recall to include the 70 to 90 million cars with ammonium nitrate inflators on the market without evidence that the fix is insufficient.
Florida senator Bill Nelson points to a wound made by schrapnel from an exploding airbag, which he likened to grenades in cars.