Twelve people were killed and scores of others injured on Friday morning when a boiler exploded at a chemical factory in a residential locality in Pakistan's eastern Punjab province, police sources said.The blast happened at about 5:30 a.m. local time (0030 GMT) in the industrial city of Faisalabad, triggering a massive fire that rapidly spread through the facility, police sources told Xinhua.Firefighters are working to contain the blaze to prevent it from reaching nearby houses, they added.The impact of the explosion caused the walls and roofs of several adjacent houses to collapse, and most of the killed and injured were...