Lightning destroyed a 150-kV transformer, which was shut down during the accident (circuit-breaker left open) and protected by a spark-gap. Subsequent to the Joule effect due to overvoltage, 38,000 litres of oil contained in the device ignited. The fire was controlled within 2 hours, yet some materials continued to burn for over 36 hours. Electricity supply to the city of Lens was interrupted for a total of 50 min. Following the accident, 45,000 litres of oil/water emulsion were recovered and stored in a tank for subsequent incineration. The soil was polluted over 200 m² area. Borehole samples, conducted in order to evaluate groundwater pollution risks, yielded a 0.003% detection rate of hydrocarbons down to a 3-m soil depth. Damages and operating losses were appraised at 7.8 million francs.