WASHINGTON — Members of a Senate committee voiced frustration Tuesday with the pace of repairs for vehicles with defective Takata air bag inflators and urged regulators to complete work on a federal rule that would require automakers to use email and other forms of electronic communication when notifying car owners about recall campaigns.

Takata air bag inflators can explode with too much force and spew shrapnel into drivers and passengers. At least 22 people have died worldwide and more than 180 have been hurt.

A years-long recall involves about 50 million Takata air bag inflators in the United States. To date, about 21 million defective air bags have been repaired.

Sen. Bill Nelson, D-Fla., said the Senate Commerce, Science and Transportation Committee recently asked the 19 automakers involved in the Takata recall to provide vehicle repair rates.

Nelson said the completion rates for the most widely affected companies ranged from Honda Motor Co., 70 percent; Toyota Motor Corp, 61 percent; Fiat Chrysler, 41 percent; and Ford Motor Co, 22 percent. He said BMW failed to provide the committee with its most recent figures.

“Overall, these recall completion rates are disappointing, unacceptable and remain a cause for great concern,” Nelson said.

Heidi King of the National Highway Traffic Safety Administration acknowledged that repair rates are “not where we want them to be.” She said the agency is exploring new ways to reach consumers and improve response rates to recall notifications.

But King could not tell lawmakers when the agency would finish writing the rule that would require automakers to use electronic communications in its recall notices as well as traditional mail.

Sen. Edward Markey, D-Mass., asked if the rule would be issued this year. King would only say it’s “in progress.”

“Send a clear signal to the industry as to what is required,” Markey said. “The longer this goes, the more endangered the public is.”