At 11:08 p.m., an arc flash occurred while an anode plane was being removed from an electrolytic bath at an aluminium smelting plant. The arc caused 100 kg of a molten aluminium oxide and cryolite bath to overflow. The contents of baths, several covers, a triangle, and a pouring gate were thrown and contained inside the potline. At 11:09 p.m., the potline’s high-resistance ground system cut off the baths’ automatic power supply. The technicians implemented the emergency plan. The potline was started back up 90 minutes after the accident. The economic losses amounted to €171,630, distributed as follows:

• material damage (cell chamber and insulation): €52,100;
• operating losses (unit shutdown when the accident occurred and cell shutdown for 18 days): €101,250;
• customer revenue loss: €18,280.

The accident was caused by multiple factors:

• instability of the bath due to a malfunction of the bath’s metering pump since its installation 20 days earlier;
• an accumulation of anode plane rise orders by the technician.

The operator noted a lack of visibility for the technician of this accumulation of orders as well as a discrepancy between the movement of the anode plane and the liquid level in the cell (immersion). 

To prevent a recurrence of such an accident, the operator:

• improved the prevention of circuit breakage by adding instrumentation to the cells;
• improved the skills of its potline workers and implemented a decision support tool.