Two labourers died from poisonous gas while cleaning a septic tank at a residential building in the municipal area of Kahalu upazila on Monday morning. The deceased were identified as Azhar Ali, 45, and Shafiqul Islam, 25, of the area. Sources said, three men went to clean a safety tank at about 10am at the building at Sajatia. As Shafiqul entered the tank he fell unconscious. At this two other cleaners got into the tank to rescue Shafiqul but Azhar met the same fate while Gafur became sick due to gas poisoning. Officer-in-charge (OC) of Kahalu police station said the two might have died of inhaling carbon monoxide (CO) gas inside the septic tank.