A lithium-ion battery was the cause of a violent fire in an automobile plant. When a technician observed on his test equipment the abnormal increase in battery temperature during installation, the battery was transported to a secure area and immersed in a large volume of water intended for this purpose. This generated a muffled detonation and a sudden outbreak of fire that did not cause any injuries. The 40 employees at the site evacuated the premises.

An analysis of the accident showed that the water cooling system of the damaged battery was leaking. The immersion triggered an internal short-circuit, causing a thermal runaway on one or more cells. Also, the immersion water was charged with salt to increase the discharge of the flooded battery. It appears that salt water amplified the thermal runaway phenomenon and generated a high release of hydrogen, which caused detonation and ignition of vapours on the surface of the water. No hydrogen fluoride emissions were observed.

After this accident, the following measures were taken:

• overhaul of emergency procedures in the event of a battery incident,
• optimisation/strengthening of quality processes for battery verification at the end of the manufacturing cycle and before testing,
• salt is no longer added to the battery immersion water,
• portable gaseous hydrofluoric acid detectors are to be worn before any handling of a faulty or suspicious battery,
• installation of specific air extractors in battery laboratories (secure areas where batteries are handled in the event of an incident or disassembly).