The Minnesota state fire marshal’s office says an overheated air compressor caused the deadly Memorial Day explosion and fire at a paper mill in Sartell. A report released this week says that the overheated compressor ignited oil vapors in an air receiving tank at the Verso Paper mill. The cooling water supply to the compressor was reportedly severely reduced in the hour before the explosion, and two other compressors had already shut off because of overheating. Damage from the explosion is estimated at $50-million. The blast killed one employee and injured a couple of others, and Verso has announced that the mill will not re-open.