In an electrical substation adjoining a nuclear power plant outside of the BNI perimeter, a fire broke out at around 3.15 pm in the oil tank of an electric transformer (step-down transformer from 400 kV to 63 kV) containing no PCB. An area 10 m in diameter was burned, threatening a 2nd transformer. Significant emergency response resources were mobilised (25 fire engines, 68 firefighters) and specialist backup teams were called. The firefighters, wearing respiratory protection equipment, used 2 deluge guns and controlled the spread of flames. A safety perimeter was set up and the electrical current was cut off for 15 min. Persistent wind diluted the abundant smoke emitted. The emergency services brought the fire under control at around 5.30 pm using foam and powder, and then continued extinguishing the transformer heads. The area was monitored throughout the night until arrival of a company the next day that was contracted to pump the 40 m³ of water and oil contained in the retention tank. The emergency services intervention ended at 9.50 pm. In order to subsequently assess and recover part of the equipment due to their high cost, during the intervention the operator had retained the option of not completely flooding the transformer, then monitored the equipment. On 26/09, officers from the neighbouring nuclear power plant noticed fumaroles on the equipment affected and informed the operator. Firefighters arrived at the scene at 12.05 pm with significant resources and noted that insulating paper had continued to burn slowly. The operator maintained its position of protecting the equipment, no intervention was started and the emergency provisions were lifted at around 1 pm. On 28/09, after reading the findings of the assessments and seeing a new release of smoke when opening a hatch, the operator requested further assistance from the external emergency services. To prevent fires from restarting, they filled the transformer’s tank with water and foam making the equipment permanently irretrievable, then continued monitoring the installations affected. No health consequence, or environmental impact or adverse effects on the operation were noted.