(Portland, OR) -- An investigation is ongoing into an explosion Sunday that blew out the wall of a four-plex apartment in Portland's Centennial Neighborhood. When firefighters arrived, they found one person who was injured jumping from a platform to escape the fire. The roof partially collapsed where the wall was gone. The building is not structurally safe, so investigators flew a drone inside to help determine the cause of the explosion. A person of interest has been interviewed, but there have been no arrests.