Pohang: Police on Monday began an investigation into a fire and multiple explosions at a POSCO factory in the southeastern city of Pohang the previous day. The fire, accompanied by multiple explosions, began at the steel company's No. 3 Finex plant at 4:20 a.m. Sunday and was completely extinguished five hours later, leaving one worker injured. According to Yonhap News Agency, the Pohang Nambu Police Station was set to summon company officials for questioning about the cause of the fire and explosions later Monday and plan to conduct a joint on-site investigation with the National Forensic Service and fire authorities on Tuesday. Police and fire authorities currently speculate that the blaze may have been caused by a malfunction in the oxygen injection vents underneath the smelting furnace at the No. 3 Finex plant. The reason why the vents did not work properly is still unknown. In March 2013, a fire broke out at the No. 1 Finex plant of POSCO's Pohang factory due to a crack in the vents.