By Scott Eisen
BOSTON (Reuters) - 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. Many were out on the streets enjoying unusually mild March weather when the fire broke out in early evening and the fire department cut power. At that point, patrons at dozens of restaurants were forced to flee into the streets. City buses helped evacuate the area. Fire department spokesman Steve McDonald said that "thick, black, acrid smoke" poured from the scene of the fire. The smoke billowed overhead as city streets were closed down, power was cut to buildings and traffic lights, underground trains were diverted and part of Interstate 90, which runs through a tunnel directly under the Back Bay neighborhood, was closed. One of the neighborhood's best known buildings, the main branch of the Boston Public Library, reported that its power had been cut off. The 60-story John Hancock Tower, Boston's tallest building, also went dark. At least 20,000 residents were said to be without power. Besides the Back Bay, power outages spread to the adjacent Theater District, Chinatown, Kenmore Square and the South End. The affected area is also home to colleges including the Berklee College of Music. "The public is urged to stay away from this area. Stay indoors please!'' the Boston Fire Department said on Twitter. The police department chimed in, asking pedestrians to seek alternate routes around affected areas. Police cruisers were stationed at many intersections in the eerily dark city streets. Later, firefighters added that "the transformer that was on fire is cooled with mineral oil. While not toxic, it is never good to inhale any kind of smoke." A number of people were being treated for smoke inhalation, local media reported. In another tweet, the department reported: "Massive blackout in area. In order to stop fire, power has to be turned off. Sheraton Hotel is now dark except for emergency light." The fire was extinguished by late evening but was still smoldering. Crews from NSTAR were on the scene. No firm estimate was available about when power would be fully restored. "Lots of people (are) working hard to get the area back up. Expect a very long night," the fire department said. The city of Boston said power outages would continue until the morning, having an impact on business, transit and the morning commute. "We hope that most of (the power) will be on by Wednesday morning, by the time businesses open at 9 or 10 o'clock," Boston Mayor Thomas Menino said, adding, "That's a guesstimate."
(Reporting by Scott Eisen; Writing by Ros Krasny; Editing By Cynthia Johnston)