The already massive Takata airbag recall is more than doubling in size.

The National Highway Transportation Safety Administration today said it is expanding the recall to include 35 million to 40 million airbag inflators to be recalled through 2019 in five phases. This tally is in addition to the 28.8 million airbags already recalled.

The safety agency described this effort as the “largest and most complex safety recall in U.S. history.”

Some Takata airbags have ruptured and sprayed sharpnel into the cabin. To date, there have been 10 deaths and more than 100 injuries in the U.S. due to this problem, according to NHTSA.

The agency said the root cause of the problem is that "a combination of time, environmental moisture and fluctuating high temperatures contribute to the degradation of the ammonium nitrate propellant in the inflators. Such degradation can cause the propellant to burn too quickly, rupturing the inflator module and sending shrapnel through the air bag and into the vehicle occupants."

NHTSA will consult with the affected automakers to determine a rollout schedule for the recall, prioritizing the highest-risk vehicles. The agency said consumers should check for information and urged people who receive recall notifications to act quickly to have the work performed.

More than 8 million airbags have been replaced with the existing recalls.

“This recall schedule ensures the inflators will be recalled and replaced before they become dangerous, giving vehicle owners sufficient time to have them replaced before they pose a danger to vehicle occupants,” NHTSA Administrator Mark Rosekind said in a statement.

Learn more about the Takata airbag recalls.