A pipeline (D = 25 mm) broke inside a chemical plant and 60 kg of white phosphorus (P) ignited in contact with air in releasing an extensive white smoke plume. The internal emergency plan was activated at 12:05 pm, and 2 nozzles were deployed and spraying by 12:10 pm. The internal response team stopped the leak and extinguished the fire by 12:25 pm. Arriving on the scene at 12:37, fire-fighters completed the sprinkling operation to eliminate any remaining flashpoints. Sand dams were set up at 1 pm to prevent water pollution. The local Prefecture published a press release.
The phosphorus transfer pipe leading from the burners was broken at the level of a sectional valve.
The day before, an intense wave of cold weather (-10°C) had caused a drainage problem on a compressor, leading to a full shutdown of installations. A restart test on line 2 during the afternoon failed at 2 am subsequent to an electrical problem due to a short-circuit in an electrical control box, that triggered the opening of the UA line controlling both the safety heat tracing and automaton. The electrical control box was isolated and the installation thereby secured, i.e. with valves in the closed position and pumps turned off. It proved impossible to close the UA line circuit-breaker, revealing a double defect: the 24-volt coil supply, and the mechanical locking spring.
At 3:30 am, the operator was finally able to close the circuit-breaker, which in turn allowed resuming tracing after 90 min of down time, yet the safety automaton (CSC) batteries were spent (shutdown longer than 4 hours); any attempt at installation restart was consequently prohibited. The automaton would authorise restart at 11:30 am once its batteries had been recharged; the leak was discovered at 12 noon.
The phosphorus was frozen following the loss of pipeline tracing for 90 min. Restoring service then allowed reheating the phosphorus, which had lost its homogeneity as a solid plug had remained downstream of the stop valve. Between this stop valve and the primary valve, the liquid phosphorus occupying the entire free volume caused a pressure rise that was responsible for breaking the pipe.
The classified facilities inspectorate requested a reliability study of the electrical supply system, given that the site operator was supposed to propose (in the event of circuit-breaker deficiency) a solution for immediately re-establishing supply to the tracing and SCS automaton. An additional electric generating set capable of restoring overall plant supply was needed to complete the backup system. Tracing was to be improved and the line’s thermocouple network reinforced with a control room relay. A procedure prohibited any attempt at restart in the absence of homogeneous temperatures. Moreover, a fire hydrant under the pipe was moved, the operations control room confined, the backup automaton battery life extended, and the welds after all pipe repairs X-rayed.
