Highway 397 was shut down for about two hours Thursday afternoon as firefighters battled a blaze in a Finley garage near Lechelt Road.
People spotted the fire coming from the shop shortly before 2:45 p.m.
Someone was working in the shop earlier in the day but had left, said Tracy Baker, the Benton County Fire District 1 public information officer.
Firefighters kept the flames from spreading but the building was heavily damaged. The cause is still under investigation.
Benton County Fire District 1 was helped by fire crews from Benton Fire District 4, Franklin Fire District 3 and Kennewick and Pasco.