A hand grenade was found embedded in the walls of the old Stafford Middle School, and 150 children and a few sheriff's deputies were evacuated from the building Wednesday.

The children were in nearby classrooms as part of the Head Start program, while the deputies were working out in the gymnasium. The former school, which had its last class in 1992, is undergoing renovations to turn it into the new home for Stafford's school administration offices.

Construction workers discovered the ordnance, which was a Mark 2 model that first appeared during World War I and was used throughout the Korean War, between two walls of the brick building, which was built in 1916.

Unsure whether the grenade was live, the Stafford County Sheriff's Department called in explosives experts from Quantico Marine Corps Base to handle it.

"We don't fool with them," said 1st Sgt. Brian Halstead, of the department.

Officials at Quantico treated the grenade as if it were active and detonated it with other explosives, Marine Capt. Stewart Upton said.

Officials are not certain when the grenade was placed in the school or why it would be there, Halstead said. A Stafford man found a similar grenade in the summer on his property in Hartwood, and it's not unusual for various types of military munitions to periodically turn up in the area, Halstead said.

"The biggest thing is they're out there," Halstead said. "Whether or not they're still live you can never say."

School officials do not view the incident as a threat to active schools.

"There are no concerns in our department to go around and check any other school," said Gregory Martin, safety and security coordinator for Stafford County Public Schools. "There's no indication of further [ammunition]. This building has been abandoned for a long, long time . . . that [the grenade] could have been there a long time."