Big bang theory: scientists say they have found cause of Takata air bag explosions

Scientists hired by the auto industry have determined that multiple factors — including moisture and high humidity — can cause some Takata air bags to inflate with too much force and hurl shrapnel at drivers and passengers.

The Independent Testing Coalition, which has been investigating the cause for the past year, announced its findings Tuesday.

Air bags made by Japan’s Takata Corp have caused at least 10 deaths and 139 injuries worldwide. The exact cause of the problem has eluded investigators for more than a decade, although more recent probes have focused on Takata’s use of a mixture of ammonium nitrate and other chemicals to create a small explosion and inflate the air bags in a crash.

The Virginia rocket science company Orbital ATK, which was hired by the coalition, determined that three factors, working together, can cause the air bags to explode. Using an ammonium nitrate compound without a moisture-absorbing substance — as Takata does — increases the risk of an explosion after long-term exposure to high temperatures and moisture. Orbital ATK also found that Takata’s inflator assembly doesn’t adequately prevent moisture from intruding in very humid conditions.

The coalition said its findings apply to around 23 million of the 28 million Takata air bag inflators that have been recalled by the US government. All of those air bags use specially formulated ammonium nitrate without a drying agent.

David Kelly, a former acting administrator of the National Highway Traffic Safety Administration and the coalition’s project manager, said that while humidity and ammonium nitrate have been discussed as factors, this is the first time scientists have determined all the factors that combine to cause the explosions. Kelly also said the design of the inflator is coming under more scrutiny than it has in the past.

Kelly said determining exactly what was causing the explosions was a critical step. Now, he said, investigators will focus on the performance of all of the inflators that are being used as replacement parts in ongoing recalls of Takata air bags. He said owners whose vehicles have been recalled should continue to get their air bags replaced while the investigation continues.