Two families have sued Ford Motor Co. and Firestone, alleging treads on Firestone tires on their Ford Explorers separated and caused fatal accidents.

The lawsuits filed Monday following the deaths of 10-year-old Athena Lingenfelser in November and the Rev. William Touchton in July accuse the tiremaker and the auto company of negligence.

Dozens of similar accidents have prompted federal traffic safety investigators to open an investigation into possible defects with the Firestone ATX, ATX II and Wilderness tires.

Attorney Gary Pajcic, who represents Michael and Alaina Culleton, the little girl's parents, and Touchton's widow, both of Jacksonville, said the tire problem becomes deadly on the Explorer because its high center of gravity makes it more difficult to control when the tread separates.

"If you're driving a regular sedan, I don't think you have to worry because you don't have the stabilization problems," Pajcic said.

Others suits over the tires have been filed as far back as 1996.

One was filed in 1996 after a Houston, Texas, television reporter was killed when his Ford Explorer flipped after his Firestone ATX allegedly blew out. In Georgia, the parents of a Virginia University college football player filed a $23 million lawsuit in 1998 against Ford and Firestone after the Firestone ATX tire on his 1993 Aerostar van allegedly separated on Interstate 95 in Georgia and the car flipped. He died from head injuries.

The National Highway Transportation Safety Administration opened its investigation May 2 after receiving 90 complaints from consumers who experienced tread separation or blowouts.

Most involved tread separation at highway speeds and came from states in the Southeast and Southwest.

The federal agency has documented four fatalities, but Joan Claybrook, president of the Public Citizen watchdog group in Washington and attorneys involved in litigation with Firestone and Ford, said there have been 30 deaths nationwide as a result of the tire separation problem.

The investigation is in its preliminary stages with letters sent to Firestone and Ford. Both companies have asked for additional time to respond.

Ford did not immediately respond to a request for comment.

Firestone said in a statement Tuesday that they have "full confidence" in the tires, almost 48 million of which have been manufactured. "They have provided billions of miles of reliable service since 1990," the company said.