In a styrene manufacturing workshop, following the failure rupture of a polymer seal (PGAC) installed on a valve flange, due to frost, 23 t of alkylates (43% benzene, 41% ethylbenzene, 16% polyethylene, and heavy minerals) leaked out for 50 minutes. This spillage was completely recovered in the effluent treatment plant installed on the industrial platform, pumped out and then sent to a specialist company for destruction. No one was injured and the workshop’s activities were not affected because the leak occurred on a pipe that was not in operation. However, benzene that had been released into the atmosphere for 2 hours was detected by the sensors on the air quality monitoring system. The operator immediately changed the faulty seal, modified the platinum plating of the circuit from where the spillage originated and checked all of the workshop’s circuits and particularly the condition of seals that were identical to the one that had failed. The pipe was completely drained in order to remove the water that it contained.