Generally when consumers take their vehicles to a dealer for a recall remedy, they leave with the peace of mind that the potential safety issue has been fixed. That may not end up being the case for more than 34 million recently recalled vehicles equipped with Takata airbags, as the parts manufacturer, automakers and federal regulators struggle to determine why the safety devices have the tendency to spew pieces of shrapnel upon deployment.

Reuters, citing industry insiders, reports that because no definitive reason has been identified for the airbag’s explosive proclivity – which has been linked to six deaths and 105 injuries – there is no way to know for certain that new replacement airbags won’t need to be replaced themselves one day.

If the separate investigations by the auto parts maker, eleven automakers and U.S. regulators find that the root cause of the defect wasn’t addressed before Takata began producing replacement parts, vehicle owners will have to endure the recall process once again.

“If you don’t find out the root cause, who knows? We may have this same discussion again in four, five, six, seven, 10 years,” David Kelly, a former National Highway Traffic Safety Administration executive now investigating the Takata inflators on behalf of automakers, tells Reuters.

Automakers have each taken their own steps to determine why the airbags explode with enough force to injure or kill passengers and drivers.

Honda – which has been linked to all six deaths related to the airbag defect – has been conducting its own tests on used and scrapped airbags.

Two employees of the company tell Reuters that preliminary testing has indicated the issue is related to Takata’s manufacturing qualities.

For its part, Takata says it is “confident that our new airbags are safe,” even as its Quality Assurance Panel continues to work to ensure “Takata’s current manufacturing procedures meet best practices.”

While the company has quietly been investigating the airbag issue for more than seven years, it has only narrowed the search to “preliminary conclusions” linked to multiple factors.

Most recently the company has used a number of processes to review more than 45,000 inflators over the last year including administering ballistic tests, dissections, propellant analysis and CT scans, Reuters reports.

When automakers began recalling vehicles equipped with the airbags in force last summer, Takata and regulators said that issues with the airbags may have been caused by the presence of moisture. That led automakers to limit recalls to areas of high humidity, such as the southern United States.

Investigators have also looked at various factors such as the design of the inflators and airbags, the shape of the explosive propellant used to deploy the bag and vehicle design as potential reasons for the defect.

Back in October, investigators began to focus on the unusual explosive chemical – ammonium nitrate – used in Takata’s airbags.

Chemicals have long been the powerful mechanism behind airbags. That’s why after some crashes, the driver or front-seat passenger in a vehicle may have chemical burns on their skin.

Typically the inside of an airbag contains an igniter that heats an aspirin-sized tablet of compressed chemical. The ensuing reaction fills the airbag with gas, inflating it at speeds reaching a few hundred miles per hour.

Takata began using ammonium nitrate in its airbags in the late 1990s, because of the chemical’s ability to make airbags inflate in a matter of milliseconds.

Officials familiar with the investigations into the airbags say the chemical is still being considered as a contributing factor in the explosions.

However, since Takata began making replacement parts for the recalled vehicles, the company has added materials that gather and hold moisture to the chemical mix in an effort to make the device safer.

“We have a lot of work to do, especially with regard to why this happened in the first place,” U.S. Transportation Secretary Anthony Foxx tells Reuters.

Despite the number of unknowns when it comes to Takata’s original airbags and its new replacement parts, regulators have said the new devices are safer.

“The concern is, are they safe over the long-term? That has yet to be determined,” Mark Rosekind, head of NHTSA, previously said.

Takata faces questions over air bag fix as recalls expand [Reuters]

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.