SEATTLE (AP) _ About 300 passengers were delayed up to an hour at Seattle-Tacoma International Airport when an old artillery shell a youngster had packed aboard a flight from Europe caused a bomb scare.

The shell, the size of two oil cans, was picked up from a battlefield in France by a teen-ager. It dropped out of a bicycle box being unloaded Friday from Scandinavian Airlines System Flight 937 from Copenhagen, Port of Seattle police Chief Ed Ingram said.

The shell was reportedly of World War I vintage. It was exploded late Friday by munitions experts at the Army's Fort Lewis, near Tacoma. It wasn't clear whether the shell could have exploded on its own.

The teen-ager was on a trip arranged through the Bush School, a private school in Seattle, said Kerri Lauman, the mother of one of four students who returned Friday and were questioned about the shell.

The students, returning from a three-month tour of France, said the boy who packed the shell in the box was still in Europe.

The students who were questioned, three girls and Ms. Lauman's son, David, knew the other student had found the shell, but thought he had heeded advice not to try to send it home, Ms. Lauman said.

The four were released after questioning, said airport spokeswoman Margo Spellman.

The shell was about a foot long and three inches in diameter, Ms. Spellman said. It was placed in a steel drum, loaded on a truck and taken to a concrete bomb bunker away from the terminal.

Leif Eie, an SAS spokesman in Seattle, said transporting the shell wasn't illegal because ''we permit live ammunition in the baggage compartment like all other carriers.''