Nearly three and a half months after a Summer Street apartment building was destroyed by a fire that claimed the life of one resident, authorities granted permission to demolish the standing but unstable structure. Operating an excavator, P.J. Weaver of Weaver Construction began tearing apart the 122-year-old two-story building at 535 Summer St., owned by Helen and Stephen Robertson, Monday morning. By the afternoon the structure had been leveled and the work to haul away the building debris was underway. Paul Weaver said the site should be cleaned up by Wednesday.