Johannesburg - A 44-year-old man is in a serious condition after the tanker, which he was cleaning, exploded.The incident happened in Chloorkop, east of Johannesburg on Tuesday, paramedics said.ER24 spokesperson Werner Vermaak said, when paramedics arrived on the scene, the man had been attended to by a local first aid team."They indicated to paramedics that the injured man climbed into the tanker to clean it. Moments later, they heard an explosion," Vermaak said.He was removed from the tanker by the first aid team and paramedics were called to the scene.Vermaak said he had sustained severe head injuries and extensive burns across his body.The emergency helicopter airlifted the man to hospital. The exact cause of the incident was not known. It was not clear what type of chemical the tanker had contained.