The Takata building in Auburn Hills, Mich., in October 2014. (Carlos Osorio/AP)

Federal regulators said Tuesday that fewer cars than first thought will be recalled for faulty air bags. The recall of cars equipped with Takata air bags remains the biggest recall in U.S. history, however, with the figure now set at 23.4 million vehicles that have been recalled.

Regulators first thought that 34 million inflators in 30 million vehicles might be subject to recall, but they said Tuesday that they discovered that some vehicles had been counted twice in the initial tally. They said that so far, the faulty bags have been replaced in 4.4 million vehicles.

They said data collected from Takata and automakers has been shared with the Department of Justice, which is considering civil or criminal action against Takata, which allegedly knew about problems with the bags without notifying federal officials.

At least eight deaths and numerous injuries have been tied to faulty air bags made by Takata, which inflate with so much force that they spray a driver or passengers with metal shards. In addition to a recall issued by Takata, 11 automakers have recalled their vehicles.

When a vehicle is involved in a collision, sensors ignite a solid wafer of chemical propellant inside the metal canister of the air-bag inflator. A chemical reaction creates a gas that inflates the air bag within milliseconds, popping it from the steering wheel or dashboard.

But if the propellant burns faster than intended, it produces more gas than the vents into the air bag can handle. The metal canister can break into fragments that injure the driver or passengers.

Takata makes one in five  air bags worldwide, has 55 factories in 20 countries and is among the world’s largest suppliers of auto parts. But the company hasn’t been able to keep up with the demand for replacement air bags, and its competitors are reluctant to ramp up production unless they get long-term commitments from automakers for their products.