At approximately 6 p.m., a polytetrafluoroethylene (PTFE) expansion boot burst, causing liquid hydrochloric acid (35% HCl) to be sprayed into a distillation unit that had been recently installed in a chemical plant. The unit had just started its test phase before being placed into production. The internal alert was triggered. Six-hundred litres of HCl were released. The platform’s firefighters were able to secure the area and stopped the leak at 6:30 p.m. The alert was lifted 15 minutes later. The solution then returned to the platform’s collectors.

The accident occurred while the first test was beginning (HCl 19%). The system initiated the automatic shutdown due to a safety device that had been incorrectly configured. The draining of the product (HCL 19%) was initiated, via the circuit foreseen in this situation. The HCl 35% circuit was isolated from the distillation column. However, a non-return valve also isolated the HCl 35%, especially on an exchanger, preventing it from returning to the pumps and to the storage tank. The circulation of the HCl 19% at high temperature in this exchanger led to the thermal expansion of the HCl 35%, its overpressure and the rupture of the weakest element of the line, i.e. the expansion bellows. The HAZOP risk analyses conducted upon receipt of the plans by the operator and supplier of the installation did not identify this scenario.

Following the accident, the operator installed a by-pass on the exchanger with a valve that is kept open. All the other exchangers underwent a thorough review, and all inconsistencies between the design pressure of the bellows and the maximum line pressure were recorded. Material incompatibilities were also found on the bellows. All components contaminated by the acid during the leak were inspected. Some were replaced, while others were refurbished.