Pollution
Humain
Environnement
Economique

A tank containing sulphonic acid overflowed during a transfer operation involving a cistern inside a detergent plant. Upon observing the spillage of sulphonic acid on the floor situated at a level of 5.5 m elevation, a design office staff member sounded the alarm, ordered the truck transfer operation to cease and duly notified the safety staff. The relatively viscous product had flowed between the building wall and the siding and then followed a path into the plant courtyard beyond the transfer zone. A thunderstorm had struck and the sectional valves on the public stormwater drainage system were closed. Nonetheless, the rainfall carried the acid into the plant’s stormwater collection network, where once in contact with water, the acid generated a large quantity of foam. A subcontracted company proceeded with pumping 12 m³ of sudsy water from the system’s main collector pipe.

The employee responsible for the transfer operation had reversed the free capacity values between two of the tanks handling bulk raw materials: 105.1 m³ for one vs. 31.5 m³ for the other. The tank featured a high level indicator associated with a visual relay in the control room, but the employee had constantly remained beside the truck from the beginning of the transfer until the time the overflow was noticed. The acid also leaked via the 15-m long vent-to-atmosphere outlet positioned at the top of the tank; under the weight of the acid spill, the vent detached. Several measures were taken: power-assisted shut-off of the sulphonic acid transfer pump at the level of the tank; installation of an audible and visual alarm in the courtyard, connected to all the high level indicators on tanks containing liquids; verification of the good working order of all high level indicators and their servo-control feature; modification of the “inventory” table to avoid reading errors; consolidation of the vent-to-atmosphere pipe on the tank; review with personnel of material transfer and safety guidelines.