A compressor located at the front end of a refinery’s catalytic cracking unit stopped running after an electrical fault. This centrifugal compressor enabled compressing gases (mixes of methane, ethane, hydrogen, nitrogen, butane, propane and H2S) originating from the cracking reaction after separation of the liquid fractions (gasoline, diesel, etc.). At first, the unit reduced its output. The site was placed in an “SO2 alert” mode to decrease its discharges, compensating for the surplus released at the flare by removing gas from the affected unit. Given various factors (SO2 notification threshold reached on the sector, announcement of Prefectural emergency measures relative to the next day’s ozone level, impossibility of restarting the unit in the near term), the refinery operator decided to close the unit altogether. During the shutdown, 233 tonnes of LPG-type gases were burned at the flare. This accident was due to a local malfunction of the compressor power supply, as a short-circuit had occurred on the cable feeding power to the equipment, which had been undersized and marked for replacement during the next down period, whether scheduled or unscheduled.