At least 20 persons were killed on Saturday when a water boiler blew up in a factory in the Bangladeshi capital Dhaka, police said. Many others were in critical condition.The explosion led to a huge fire in the Tampaco Foils factory in Gazipur area around 6 a.m., bdnews24 reported, citing Senior Fire Station officer Mohd Rafiquzzaman.He said 20 firefighting units battled the flames, which caused two floors of the five-storey building to partially collapse.Seventeen bodies were sent to Tongi Hospital and three to the Dhaka Medical College and Hospital, the Daily Star reported. A total of 74 others were injured, many critically, police said.