According to IMCA's report, when the battery was charged, the temperature inside the affected battery increased beyond the critical level. Given that the heat couldn't dissipate fast enough, the chemical reaction inside the battery accelerated. This resulted to an even higher charging current and heat generation.

IMCA states

Heat generated in the battery cell had occurred without any warning signs.

The investigation showed that the battery was at the end of its life, therefore vulnerable to thermal runaway. The heat made the battery pressurised and deformed. In addition to design life, overcharging, internal physical damage, internal short circuit or a hot environment are all potential causes for battery fires or explosions.

Actions taken

  1. Depending on the battery configuration: Isolate the battery or string of batteries or turn off the charger;
  2. Cool the battery and ventilate the room.

Lessons learned

  1. Ensure all batteries are subject to periodical inspection and maintenance; consideration may be given to inspection by infra-red camera to look for hotspots;
  2. Report any sign of external damage;
  3. Ensure that battery chargers and procedures are correct for the battery type;
  4. Consider the installation of a “thermal runaway monitor” on battery packages (UPS);
  5. Batteries should be in rooms suitable for batteries with the required ventilation, fire detection and fire-fighting capabilities;
  6. Ensure there is a specific risk assessment and transport/disposal plan relating to the removal of faulty batteries, with specific care being taken to identify the correct personal protective equipment (PPE) to be worn, and any transportation necessary.

See more:

Lessons learned: Main engine turbocharger lagging on fire

Lessons learned: Space heater catches fire