(Tualatin, OR)  --  Investigators are trying to find out what caused a fire that destroyed a family-run business in Tualatin.  Authorities say firefighters were sent to the Clark Lumber and True Value Hardware store on Southwest Nyberg Street around 2:30 yesterday morning.  Crews reported having to stay outside the steel-frame-and-concrete building because the contents that burned made the inside feel like an oven.  The store reportedly had been in business for 50 years, operated by the same family.  No injuries were reported.