At 2:50 a.m., in a metallurgical plant, a leak of sodium aluminate was noted on a valve in a 3,000 m³ tank within the alumina production unit, producing a visible 10 m geyser. The operator activated the emergency response plan. The tank contained 1,000 m³ of soda ash and 1,000 m³ of alumina. One thousand cubic meters of this mixture was recovered by direct pumping. The other half flowed into the tank’s retention area. Part of it was pumped into the ump of this retention area, but the pump was unable to remove all the effluent, and the other sumps were blocked and therefore unable to fulfil their role. Some of the effluents flowed out of the sump onto the site’s roadways. The fire brigade was unable to close the manual valve due to the soda geyser. The leak was stopped at 9:30 a.m., although pumping continued the following day, mainly because the rain began filling the retention areas.

The incident occurred at a time when the tank customarily used for the process was undergoing maintenance. Using another tank during this maintenance phase requires that the orientation of the elbow on the pump’s intake line be changed, and thus also the associated dilatoflex (rubber sleeve held between two steel flanges between the tank’s pump and the elbow designed to absorb pump vibrations). The leak had occurred on this dilatoflex installed for maintenance purposes. The accident analysis of the incident showed that the elbow had not been properly aligned with the pump, causing stress on the dilatoflex. The expansion joint disintegrated after 20 minutes of pump operation. The operator noted that the assembly’s acceptance form had not been completed during the installation process. The subcontractor who worked on the installation did not have access to the installation documents and operating instructions. “Twisting of the dilatoflex” was nevertheless mentioned on the duty roster. The dilatoflex assembly was accepted by the shift supervisor, who has no technical competence to validate this point. No procedure had been established to validate the dilatoflex assembly. Furthermore, the fact that it was impossible to isolate the leak upstream (no automatic valve installed or access to close a manual valve) did not limit the leak’s effects. One of the retention areas designed to absorb the discharge from the tank proved to be insufficient.

The operator developed the following plan after the accident:

• improve the validation of the dilatoflex installation procedures;
• check the ones recently installed;
• establish training courses on how to assemble these dilatoflex elements;
• assess the faulty equipment;
• update the major risk study on the possibility of a critical compensator failure;
• improve the retention area to prevent further overflow in the event of a decompressor leak.