Kolkata, Feb 7 (Reporter) At least four people were killed, three of them women, and another woman was burned critically in an explosion at a firecracker factory on Friday in West Bengal's Kalyani area of Nadia district, official sources said The critically injured woman was admitted to the Jawaharlal Nehru Hospital in Kalyani. The firecracker factory, stated to be illegal, was reduced to ashes on Friday noon. Sources said all the victims were probably the workers of the illegal firecracker factory. The factory was located in a densely populated Rathtala under Kalyani municipal ward No 20, where a law enforcement agency from Ranaghat Police station reached for investigation. Fire Brigade sources said the explosion occurred at around 2:30 pm impacting huge volume flames, which were brought under control within an hour. The Fire Brigade sources said they were not certain of any survivors in the explosion area, where everything was reduced to ashes, sources added...////...