Three labourers died and another fell sick after inhaling poisonous gas after they entered into a septic tank of an under-construction building in Nagolkot Upazila town yesterday morning. Police said labourers Habibur Rahman, 19, and Abdullah, 20, fell sick when they entered into the septic tank of Nasiruddin for repairing. Hearing screams, another labourer Monir Hossain entered into the tank to save them but he also fell sick. The three workers died within a very short time while another worker Ibrahim fell sick during the incident. On information, police rushed to the spot and recovered the bodies.