Twenty-four people left their farm homes overnight after the Air Force detected an unidentified vapor in an underground Minuteman III nuclear missile silo, officials said Tuesday.

Preliminary tests found nothing harmful but further tests were under way, said an Air Force spokesman, 1st Lt. Darian Benson.Citing longstanding policy, Benson would not disclose whether the missile was armed. The 60-foot, 78,000-pound Minuteman can carry three warheads.