In a polyurethane foam factory, during the transfer of polyol from tank no. 13 to no. 14 using a pump dedicated to this purpose, tank 13 suddenly deformed after 3 hours 25 min of transfer (at a flow rate of approx. 90 l/min). The operation was immediately stopped by manual override. This accident was caused by tank depressurisation resulting from non-compliance with instructions during the transfer step: the compressed air circuit, intended to fill the tank with a slight pressure surge (0.1/0.2 bar) when extracting product, had not been used.
The personnel had incorrectly assumed that air intake into the tank passed by an air circuit that in fact had been fitted with a check valve. Moreover, the rather cold temperature of the transferred material had prevented occurrence of the cavitation phenomenon in the displacement pump during tank depressurisation. Following this incident, factory production was immediately halted; the circuits were isolated and placed in safety mode. Tank deformation was severe enough to render it unusable, as were some of the associated pipes. Nonetheless, no material leak was detected. Over the ensuing days, the tank was drained for expert appraisal, and all waste was discarded.
An investigation was conducted by an external firm to identify or confirm the technical reasons leading to this incident prior to tank removal and destruction. The operating mode for transferring raw materials was analysed to determine the networks capable of performing under atmospheric pressure and those requiring compressed air. The plant operator was requested to submit to the inspection authorities for classified facilities the set of measures adopted in the near term for other potentially concerned installations, along with a detailed incident report describing the circumstances and the various causes and measures implemented to avoid the same type of event from recurring. The installation was rebuilt in strict accordance with technical recommendations issued subsequent to a study conducted by the firm assigned the investigation.
