Pro­pel­lant ‘ fix’ may not stop airbags ex­plod­ing

The Witness - Wheels - - INDUSTRY - AL­WYN VILJOEN

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.

Tem­po­rary so­lu­tion

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.

PHOTO: JA­PANESE TIMES

Florida sen­a­tor Bill Nelson points to a wound made by schrap­nel from an ex­plod­ing airbag, which he likened to grenades in cars.

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