Wednesday, March 14th, 2012 — A three-alarm fire in an electrical transformer in a popular Boston neighborhood caused a massive blackout on Tuesday, plunging part of the city into darkness, disrupting public transport and briefly prompting authorities to urge residents to stay indoors because of fears of toxic fumes. Firefighters responded to a fire in a 115,000-volt transformer at an NSTAR substation located in a garage close to the Back Bay Hilton, a 390-room hotel. The densely-populated, upscale neighborhood affected by the fire is usually crowded with residents as well as tourists frequenting shops, bars and restaurants on Newbury and Boylston Streets.