The headquarters of the North American Aerospace Defense Command, or Norad, in Colorado were evacuated for about four and a half hours on Thursday after employees found five suspicious packages, but the command’s control room team was working at a backup location eight miles away, and no essential missions were disrupted, officials said. Employees became suspicious because the packages looked out of place, said Jeff Bohn, a spokesman at Peterson Air Force Base in Colorado Springs, where Norad is based. He declined to say what appeared to be amiss. Tests ruled out chemical, biological and radiological agents, he said. Other tests were being conducted.