Holly Springs firefighters responded to a transformer overheating beside Tyson Drug and Wright Family Medical Sunday afternoon. Chief Rodney Crane said a passerby saw smoke coming from the transformer and reported it. When firefighters arrived, streets were blocked off from traffic first to secure the area. Crane said the transformer continued to overheat as it was energized, causing the oil inside the transformer to boil inside, then over-boil, exploding the tank and producing a fireball. Three transformers were actually replaced by the Holly Springs Utility Department, according to general manager Bill Stone.