A monomer vinyl chloride (MVC) leak occurred on a 27-m³ autoclave in a polyvinyl chloride (PVC) workshop at a chemical plant. Monomer polymerisation was dispersed in water at 6 to 9 bar of pressure and a temperature of 40° to 70°C. At the end of the afternoon, an abnormally high concentration of MVC was detected inside the building. A management alert was sounded 30 min later, and the internal emergency plan triggered 50 min beyond that, with internal responders on the scene for 2½ hours. In all 5 tonnes of MVC were dispersed into the atmosphere without igniting. A pivoting lid, supporting a rupture disc and safety valve, was fastened onto the reactor. This assembly was sealed by clamping 2 jaws, and then a mechanical safety feature (gate) prevented any subsequent handling of the clamp levers. One of the jaws had failed to be clamped (human error). The gate was adapted to require preliminary clamping of both jaws prior to installation; the internal emergency plan was modified as a consequence.

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