Pollution
Humain
Environnement
Economique

At a petrochemical site, an operator making rounds detected that a styrene tank had overflowed; approximately 10 m³ of product had spilled from the atmospheric venting and was flowing along the wall. Provisional measures were rapidly taken to limit the consequences of the incident as much as possible: the transfer pump was immediately stopped, ground washed with water to make the styrene float which would then be pumped off and incinerated; the polluted portion of the soil would be excavated and incinerated; the water table analysed and purified by pumping. In the scope of corrective actions, the operator modified the level measurement so that it would be insensitive to pressure variations in the tank. The incident originated from slight overpressure in the styrene tank and led to a malfunction for the level measurement instrumentation and the transmission of erroneous information (low level in the tank) to the automatic styrene transfer system from a 3,500 t tank to the 60 t tank in question.