Amidst a series of massive vehicle recalls worldwide, Japanese automotive parts supplier Takata Corp has modified the composition of an airbag propellant that contains a volatile chemical, it told Reuters.

A Takata official told the news agency that ammonium nitrate was still part of the mix, but did not divulge details of the composition change. He said the modification was made as part of kaizen (continual improvement), as opposed to addressing a defect.

“There is no admission of a defect with the original version. There has not been any finding that ammonium nitrate or the earlier composition was somehow flawed. We changed the composition in an effort to improve quality,” Reuters quoted him as saying.

The official said this updated propellant mix is used in replacement airbags fitted to recalled cars, but declined to reveal when the change was made, how many vehicles have received the new mix in their airbags, which models, or whether the new mix was cheaper than the previous one. “There have been no problems with the new versions so far,” he said.

Ammonium nitrate is a chemical usually found in fertiliser and explosives, and some of Takata’s rivals use guanidine nitrate, which is less volatile, as the main ingredient, Reuters reports, citing people close to the companies.

The previous propellant composition, Takata has said, if exposed to moisture or improperly processed, can cause the airbag inflators to explode and spray metal shrapnel inside the car. Its airbags have been linked to at least four deaths in the US and are the subject of a US regulatory investigation and many worldwide recalls in the past six years.

Reuters reports that according to industry estimates and company data, Takata has produced more than 100 million inflators since 2000, and globally, upwards of 17 million cars equipped with Takata airbags have been recalled in the past six years.

However, a Reuters analysis of internal Takata documents has found that there are millions more cars fitted with Takata airbags that have not been recalled, and there has been no evidence of any airbag-related incidents with these vehicles.

“There is no evidence that all Takata airbags produced over the past 15 years pose a current danger to the driving public, and it would be inaccurate to make such a claim,” said the US National Highway Traffic Safety Administration (NHTSA), according to the report.

“There is evidence, however, that certain Takata airbags inadvertently exposed to excessive moisture during manufacturing or regions with consistently high temperatures and humidity pose a safety risk.”

Toyota has recalled 247,000 units of the Corolla, Matrix, Tundra and Sequoia as well as the Lexus SC in humid regions in the US, while the NHTSA has issued an urgent alert for the 7.8 million owners of cars involved in the recalls in the US, urging them to get their cars fixed immediately. In all, around 14 million cars have been recalled worldwide so far by Toyota, Nissan, Honda, Mitsubishi, Subaru, BMW, Chrysler and General Motors.

Closer to home, UMW Toyota has recalled 18,700 units of the 2000-2003 Camry and Corolla Altis, Edaran Tan Chong Motor (ETCM) recalled four units of the CBU first-generation Nissan X-Trail, while Honda Malaysia recalled the 2001-2003 Stream, 2002-2003 Jazz, 2003 City and 2003 Accord.