A phosphorus trichloride (PCl3) leak occurred in a chemical plant during an iso container filling operation. The operator stopped the loading operation when the control room noticed a cloud of PCl3 and hydrogen chloride (HCl) being released into the atmosphere. The establishment’s internal contingency plan was initiated. The internal rescue services set up a water curtain. In the two neighbouring plants, the cloud of gas caused extreme irritation to the eyes and throats of roughly ten individuals. As the plant managers were unable to locate the source or nature of the gas, they decided to confine their personnel for approximately 20 minutes. The accident was caused by an inversion of the iso-container’s supply and degassing lines. This type of container was being used for the first time at the site. After preliminary testing (including the verification of the automatic valves), the operator connected the degassing pipe on the valve equipped with a coupling identified as N2 and the loading pipe on the valve equipped with a coupling bearing an eduction tube symbol. The overfill capacitive probe was in place on the degassing branch connection. During the loading operation, the overfill probe alarm was triggered 3 times. Each time, the operator stopped the pump, closed the valves and checked the container. As nothing abnormal was detected, he acknowledged the fault and continued loading. After the 3rd alarm, liquid PCl3 overflowed via the degassing pipe even though only 3.45 m³ of PCl3 had been transferred (container capacity = 14.6 m³). Analysis of the fault tree showed that a marking error on the iso-container’s connecting points was the cause of the accident: the couplings installed above the valves were reversed. The filling operation was thus performed via the degassing valve and as the tank was being filled, the pressure of the pump caused the PCl3 to return via the eduction tube attached to the filling valve connected to the degassing pipe. To prevent this type of accident happening again, various measures were undertaken: development of a receiving approval system for new packaging, a reliability study of the capacitive probe, PCl3 leak prevention procedures and start-up of the emergency fire-fighting unit… Henceforth, the neighbouring plants will be included in the site’s internal contingency plan alert procedures.

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