A Frederick County man was killed yesterday when a homemade bomb he apparently made exploded behind his home, said a spokesman for the state fire marshal's office.

Deputy State Fire Marshal Bob Thomas said the victim, Ralph King, 22, of the 4700 block of Ijamsville Road in Ijamsville, was behind his house and between a three-car garage and a storage shed about 4:50 p.m. when the bomb exploded.

Thomas said the explosion broke both of King's legs and blew off his left hand above the wrist.

Thomas said the explosion was heard for several blocks and threw pieces of metal some 200 yards.

He said King's body was found by his wife, Stacey, who called the fire department.

King was airlifted by State Police Med-Evac helicopter to the Shock-Trauma Unit in Baltimore, where he died shortly after arrival.

Thomas said an investigation was under way to determine why such a powerful explosive device had been made.