A worker died and three others were injured in an explosion at a sponge iron factory in Chhattisgarh's Raigarh district, police said on Friday.The incident took place at Navdurga Fuel Private Limited near Saraipali under Punjipathara police station limits, a senior official said.The deceased was identified as Narendra Singh (32), a native of Bihar.Bhim Kumar Das, Umesh Koda and Jaswant Kaur were injured in the incident and undergoing treatment at a private hospital.Hot material jammed in induction furnace-3 of the plant resulting in the explosion and hot ash fell on the victims, police said based on primary investigation. They were rushed to a nearby private hospital where Narendra Singh succumbed during treatment.