Sartell (AP)-One person was killed yesterday and at least five others were injured in an explosion that caused a large fire at a paper mill in Sartell.  An air compressor apparently exploded at the plant shortly before 11:30 a.m.  Three of the injured were treated at St. Cloud Hospital and released.  The Verso Paper mill recently celebrated its 100th anniversary. The mill employs about 260 people and is the second-largest employer in the town of about 16,000. About 50 people were working at the time of the blast.  At least one firefighter was treated for heat exhaustion. At least 15 fire departments responded to the blaze.