At around 5:55 p.m., a fire started during an operation to unload a bucket of spent NiMH (nickel-metal hydride) batteries into a skip that was to be charged into an arc furnace at a steel mill. Flames and white smoke rose up from the skip. The fire concerned the batteries’ plastic wrap. The workers covered the fire with sand. Firefighters extinguished the fire with foam. The scrap metal and burnt batteries were recycled in the plant’s arc furnace.

The root cause of the fire was failure to take into account the particularly high flammability of the new waste charged into the furnace. Although rare, the operation of unloading a bucket outside the furnace due to a cancelled casting operation had been done before and there were no issues when non-combustible scrap metal had been loaded. However, the new operations for recycling metal-bearing waste and plastic-wrapped NiMH batteries in particular were not suited to the old practice of lighting the rope holding the bucket to make it release its load. When the rope was lit, the batteries at the bottom of the bucket and in contact with rope also ignited, setting fire to their plastic wrapping. The practice of unloading buckets outside furnaces was not set out in a procedure.

Scrap metal covering the batteries in the skip made it impossible to quickly extinguish the fire.

After the fire, the operator took the following actions:

• changed the procedure so that rope no longer has to be burnt when unloading buckets outside a furnace;
• told technicians to be vigilant about changes in work situations and to contact the support departments (such as HSE) when faced with a new situation for which there is no procedure.