Students and faculty evacuated the building prior to the start of school Wednesday as fire alarms started sounding at 8:05 a.m.  The local branch of the Chesterfield County Fire Department arrived on scene within minutes of the evacuation to determine the cause of the alarm.  According to school front office personnel, a faulty sensor on the smoke alarm panel caused the system to fail, resulting in an alarm.  Firefighters fixed the issue within minutes of the arrival.  Students and staff safely re-entered the building by 8:30 a.m., and most first period classes started by 8:35 a.m.