DULUTH, MN (KDAL) - The Duluth Fire Department responded to a fire at 2631 West 4th Street just after 1 a-m on Wednesday.  Crews found an upstairs bedroom heavily involved in fire when they arrived and were able to extinguish the blaze and prevent its spread.  The lone occupant was able to escape the fire without injury.  Damage estimates are said to be between 15 and 20 thousand dollars.  The cause of the fire is under investigation.