(Portland, OR)  --  Investigators are trying to determine the cause of a fire that displaced nearly 100 residents of the Hotel Alder in downtown Portland.  Authorities say the fire quickly elevated to three alarms yesterday afternoon at the building on Southwest Alder Street and 4th Avenue.  Most residents got out safely, but firefighters had to rescue several who couldn't escape on their own.  A temporary shelter for the residents was set up at the First Christian Church on Southwest Park.