For the second consecutive year, Boston had the lowest number of fire deaths for large cities, recording one fatality in 2012, fire officials said Monday. One person died in a Dorchester apartment building fire on Jan. 3, 2012, Boston Fire Department spokesman Steve MacDonald said. In 2011, there was one fatal fire, 2010 had two fire deaths, and no one was killed in 2009, he said. MacDonald attributed Boston’s low fire fatality rate in part to the city’s commitment to fully staffing the department. Some 50 new recruits are joining the department in February 2013.