The 911 report and sound of sirens indicates a house fire in the 900 block of 20th Ave, just a bit south of Union.
cdguy is on the way to check it out.
Update: SPD is redirecting traffic at Union and Marion. And here’s the house that’s involved according to Google StreetView:
Update x2: Scanner says fire was on the back side of the house, and appears to have began on the exterior. Fire marshalls on the scene.
Update x3: cdguy just got back. Firefighters apparently have the fire under control. Said no flames were visible, but there’s a heavy smell of smoke in the area. People at the scene were speculating that it was caused by a BBQ.
Update x4: I spoke to Dana Vanderhouwen at the Fire Department, who said that the fire was ruled accidental, caused by placing some paint brushes near a working water heater. Damage is estimated at $100,000. As commenters have said, the home was vacant and there were no injuries.
Here’s another image sent in by Joanna: