CHELSEA, Mass. — Residents were evacuated Sunday night after a large section of the front exterior wall of a residential building on Orange Street collapsed, leaving bricks scattered outside and raising concerns that more of the structure could fall. The collapse happened around 8:30 p.m. Sunday, Oct. 11, firefighters said. No injuries were reported. Fire crews characterized the damage as a significant structural collapse and evacuated the building as a precaution. Residents were sheltered from the rain aboard an MBTA bus. Orange Street was closed for several hours and had reopened to traffic by 6:30 a.m. Monday. The cause of the collapse was not immediately known. Building inspectors remained at the scene Monday morning as officials assessed the building and the risk of further failure.