A house fire on McColley Road in Milford Thursday night is under investigation by the Delaware State Fire Marshal.  Investigators have determined the blaze began on the first floor when an operating liquid fueled space heater malfunctioned.  Carlisle firefighters found the two-story home heavily involved in flames when they arrived around 11:30pm.  The occupant of the home was treated for 1st degree burns to his hands and face at Bayhealth Sussex Campus.  Two firefighters were also treated for minor injuries and released.  The Red Cross of Delmarva is assisting the residents – damage is estimated at $70,000.  Several area fire companies provided assistance and cover.